GR mini's project page

Cleaning the chain

2010-10-14T03:44:00.000-07:00

Simple tutorial this one but essential none the less.

Minimoto chains aren't o ring type like most motorcycle chains, they're just a very basic type working on metal on metal contact between the links. This means their life span is alot shorter but given the minimal amount of hours the bikes are used this isn't really an issue.

However due to the tiny size of the pinion sprocket and the rather huge RPM's they see, to get the most life and reliability you can from them its essential to keep up good maintenance.

So im a believer in cleaning it after every race meet along with a few other things ill post on later and of lubing the chain after every use. It seems to be the only way to get a decent life span from the standard chains. So here goes.

The tools you'll need. A 4, 5 and 6mm allen key for removing the appropriate parts, a chain breaker for the minimoto size chains and a brush along with either some petrol or kerosene.

1) Remove the footpeg bracket to get access to the chain. Unfortunately you cant take the chain off without breaking it due to the swingarm caging it in and these types of chain are continuous, not held together with a master link. thus the need for a chain breaker.

2) Next, slowly rotate the rear wheel and observe the chain links as they roll off the pinion sprocket. They should all roll of straight and unkinked. If they do roll off kinked its time for a new chain. Heres a picture of a worn out siezed chain that must be replaced.

Fortunately this one seems okay :)

3) On this bike the water pump mounts to the clutch bell and the belt is driven via the pinion, so Those must first be removed. First pop off the belt then remove the two bolts holding the pump on.

4) The 4x bolts holding the clutch cover on can then be removed and the cover removed in turn. This then allows you to take off the chain.

5) Pop the chain off the rear sprocket. Now is a good time to inspect the condition of a few parts. The chain slider - This one is in fine condition

Check both front and rear sprockets. They shouldn't be worn too thin and pointed at the tips and shouldn't have a hook pattern too them. These are both fine.

6) Now to remove the chain, a special tool is needed called a chain breaker. you can get them from most pocket bike part suppliers. What this tool does is to push a pin from the chain straight out so the loop can be broken. Here's the buisiness end of the tool. The flat tipped screw clamps the chain to keep it in place and the pin shaped one pushes the chain pin out.

So Grab the chain and place it in the chain breaker. The pin shaped screw should be aligned with one of the chain pins and the clamping screw firmly holding the chain in place as shown.

Then screw in the pin shaped screw and out should come the chain pin! After backing off the screws and removing the chain it should then simply pull apart.

7) Grab a container (a fuel safe one) and fill it up with a bit of either kerosene or petrol. I use petrol because there's plenty of it about and its not a requirement to use kerosene on these chains as they have no O-rings to be ruined.

Put the chain in and stir it around with your brush a little. all the grime and dirt should loosen up eventually. Generally i leave the chain in for an hour or so until the petrol is filthy.

Ready!

8) Take the chain out and sling it around something and let the excess petrol/kero drip dry off it. Excuse my bodgey jig.

9) While your waiting for that to dry grab the brush and petrol and clean off the sprockets, front and rear. Just dab some petrol on the perimeter of each then wipe it clean with a rag after a minute or two.

Nice and clean!

10) Now take the freshly cleaned chain and loop it around the swingarm (dont make the mistake of joining it without doing this! its mega annoying) and put it back in the chain breaker. this time you'll put the pin in the flat ended screw and use the pin ended screw to clamp the chain. Then just simply wind the screw in to push the pin back in to the chain and join it.

11) Nearly there now. Simply install the chain back on the rear sprocket, put it around the pinion and bolt the clutch cover back in place and the water pump. MAKE SURE TO INSTALL THE O RING BELT BEFORE THE CHAIN!

12) Last step is to lube that sucker up :) Grab a can of chain lubricant. I just used any old brand i could find. Given the amount of times you lubricate the chain (once every use) the quality of it i doubt matters.

Then holding the tube against the BOTTOM of the chain spin the rear wheel while applying a generous amount for about two full revolutions of the chain. You must do this once after every use/ride to stop the chain binding up.

Now your ready to go! once you've done it once or twice the entire process should only take about 10 minutes. Well worth it for a long life chain :)

MEGA MOD! making new chain adjusters for the cag

2010-10-08T02:40:00.000-07:00

So as promised here it is. Probably one of the trickier projects due to having to mill steel (always tricky) but the reward is well worth it.

As anyone thats owned a cag will know, trying to remove the rear wheel to change the sprockets or tyres over is the most nightmarish procedure known to mankind. you have to try juggle about 6 pieces at once to stop the entire axle assembly falling out backwards and even then the setup is still pretty dodgy.

Determined to just rid myself of the entire setup completely... dodgy tube spacers, crushed box section adjusters and all.. i angle grindered the entire rear end in more or less a fit of rage :P Fortunately the frame is pretty thick around the swingarm.

As always the trusty cad program provides the design to work with. Heres the initial render of it. The only design change was to eliminate the rounded corners on the ends because i couldn't easily replicate them on the manual milling machine.

With that done i grabbed the nearest size of steel i could find, which turned out to be some 32mm diamter steel rod, chucked it in the lathe and faced it off then end drilled it for a 6mm clearance hole. Its reason will become clear later on.

The rod was then parted off with a hacksaw at 62mm length and refaced and the edges chamfered. Now i can move over to the mill.

The rods are 32mm diameter and they needed to be 16mm thick. Thus i had to machine off 8mm of thickness from each side - quite a bit! Accuracy wasnt paramount so i just touched the tool (80mm carbide face mill) to the top and used to the DRO to set the depth.

Taking the first cut. Depth of cut was 1.5mm to begin with but using the handy gwizard calculator i ended up getting it down to 2mm with a quite reasonable feed rate. well recommended!

Nearly there.. last cut on this side. The coolant really helps with these heavy operations.

The part is then flipped over and rested on a set of parallels to keep it.... parallel :P while the other side was machined.

And the part at this stage with a piece of the original rod.

After making two identical pieces shown above it was then time to make the first slot for the axle to go through. There needs to be two - one 19mm and one 10mm (the axle diameter). so the 10mm was done first.

One of the best tips when it comes to milling is that drilling removes the most material for per unit of time of nearly every tool. So for an operation like slotting drilling a series of holes reduces tool wear infinitely and allows the end mill to basically finish the slot off.

Here the stock is being drilled with a center drill before final drilling to 10mm, then the completed holes with a 10mm carbide end mill in the collet chuck ready for finishing. The digital read out makes this a doddle.

First pass with the end mill. Not tempting fate with steel the cut depth was only 2mm. With coolant it chewed through like it was nothing.

And all done. The finish is very ordinary because i just did the slot in one pass. The proper way is to drill the holes smaller to say 8mm then make a 1mm cut either side of the slot to finish it off. Given how long it took to mill the single slots and the fact accuracy wasnt critical, i wasnt too concerned.

Next was the big slot the adjuster itself sits in. the cad called for 20mm but the closest end mill was 19mm so that was used instead.

I didnt grab a picture of it but i used an 18mm roughing bit to do the initial slot then finished it off with the 19mm using the aforementioned process. Heres the first pass at 2mm depth.

And at final depth, but using a standard carbide tool to do some gentle cutting passes for a good surface finish.

Done :) the finish on the 19mm slot is great as you can see, the 10mm not so much so, so that shows why you need to cut the slot undersize initially. Mind the rough edges at this stage, it still needs cleaning up on the mill.

After completing the 2nd one it was back into the mill to clean up all those nasty edges and start on the "nubs". These parts will fit into the ends of the box section to provide some strength in addition with the welds and also to help locate them while they are welded.

Nothing too special with the process. just cut down with the 10mm end mill. Heres the finished part.

Nearly there! The chain adjusters themselves were next to be made. nothing too hard. drilled out some 20mm rod to 10mm, then turned the outside diameter to 19mm and parted it off. The edges were then rounded off with a knife tool as seen here.

Drilling the edges and tapping them for M6 threads means the machining is done! The finish is hardly perfect but for a compartively small mill its more than acceptable to me.

Back at headquarters the pieces were lined up and welded with the TIG. And here they are all welded in. I reckon they look pretty damn good :)

All that remains now is to get a new decent axle and make some axle protectors for the ends. Then the spacers will also need to be redone and the chassis painted/powder coated.

So thats it! Hopefully your all still awake by the end of this :p

Now i need to go pick the swarf out of my hair.. ughh..

Bigger boost ports!

2010-10-04T18:18:00.000-07:00

Plenty of material to upload so keep your eyes peeled over the next week!

I've touched on this subject plenty of times, and that is boost porting cag barrels. The possibilities are almost endless for how many ports you cut in, how tall they are etc etc. So im just slowly going through them testing what works and what doesn't.

This is barrel number 5 to get tested. Nothing too special aside from a few pics to show how i do it as i didnt have many in the last blogs ive mentioned it.

Borrowed a friends milling machine as mine is still halfway through an upgrade. A little overkill perhaps :P

I had a jig made up that was a big angle plate and the exhaust port bolted to it, but clamping it in the milling vice worked just great surprisingly. i was expecting the fins to break but the cutting forces are so low on account of the metal being so weak, its not a problem.

Taking the first few cuts with a 1/2" ball nosed end mill. Id already had a single 1/2" port milled in. im just enlarging it on each side (not giving away any figures unfortunately :P)

Tadaaa. The ports all done now. This kind has been refered to as a "3d" port. All that remains is to change to a square shoulder end mill and clean the piston skirt up.

One complete barrel! Fortunately/unfortunately (which ever way you look at it i guess ;p) The ring locating pins now interfere with the port, so ill either redrill the locating pins or upgrade to a billet flat top piston. I think i know which one ill be doing!

For any queries about having this work done to your own cylinders/barrels shoot me an email at Glen.M.R@gmail.com

The definitive guide to removing stuck bolts

2010-09-16T17:39:00.000-07:00

Nothing to report on the bike side of things but you can have a handy hint from experience today :P

Theres many ways to remove stuck bolts - screw extractors, freeze spray, impact drivers etc etc. But from experience none of them work that well on a properly siezed fastener.

Now if i cant get the bolt to come free with a blast from the propane torch, Its straight out with the welder to remove it. Because this is about the only way to get them out once they're wedged in good. This is, ive found, to be the ONLY way to get them out.

As an example heres one of my lathe tools. it has a small grub screw in it that holds the carbide tool on to it. Unfortunately 4 years of being outside has taken its toll and the grub screw is now rusted in. Freeze spray and heating it did nothing as expected, and the impact driver handily rounded out the hex socket in the middle.

So out came the welder. First is to find a sacrificial item. This worn out allen key bit will do just fine. ive ground it down to the right size and just bashed it in with a hammer nice and tight.

Next is to weld the two together! (who'd have thought). This gets the bolt out in two ways. The first is the immense heat from the welding process is enough to loosen any stray loctite or rust thats siezing the two pieces together, and second its a strong connection between the allen key and the grub screw that allows alot of torque to be applied for removal.

The completed weld. Being careful not to weld the grub screw to the lathe tool itself. That would not help our situation much :) You dont need much current either. this was only 40 amps.

Tadaaaa. The rust on the grub screw can be seen here. Quite alot of the rust came out as powder while it was being undone so it shows that the welding loosens it up in that regard. In the future i'll have to oil them regularly.. One of the downfalls of working outside. One day ill get that indoor workshop.. hahaa.

Till next time.

Remounting the steering damper

2010-09-04T23:55:00.000-07:00

Just another little convinience job.

The original place the steering damper mounted to worked okay, but it looked akward because it jutted out of the forks at a wierd angle and it didnt feel very progressive at all.

In addition to fixing those problems i wanted to remounted it to give me more room up the front for other parts and also make adjust it easier.

First job was to cut off all the original mounts from the current front bracket and weld on the new one. Its much smaller and takes up a hell of a lot less space. just some 10mm steel ground into shape with an m6 hole tapped into it. here it is ready to be welded on with the TIG.

After all that was welded and painted on to the other end of the steering damper. The plan was to mount it using the fork clamp bolts, which are M5. but i discovered my BMS damper uses m6 bolts.. ugh.

So i had to make a tricky little mounting spacer/shim all in one. It pushes into the damper eyelet and shims it down to an m5. Works great and looks pretty schmick!

Over all it looks much better, it's easier to adjust and it takes up less space + weighs a tad less. So all in all a good mod :)

Metal coolant lines

2010-09-04T00:32:00.000-07:00

A persistant problem ive had, and no doubt every other banshee owner has had, Is the coolant bottle getting in the way of everything.

The problem was semi rectified by changing to a smaller GRC coolant bottle but another problem remained in that the coolant hose ran in between the fork and frame and was constantly getting crushed limiting steering lock (not that you use that much anyway) and damaging the hose.

I tried running the hose around the outside of the fork but found it was bending the outlet on the radiator and it looked rubbish.

So i decided to find a way to route the thing out of the way of the forks. The only place i could see was around the radiator, but no way could a 20mm diameter hose fit through any gaps there. But a 10mm one could...

In the past ive made metal coolant lines for the bike. This helps the bike cool off faster once its switched off, and contributes a little to cooler running. Plus it looks awesome :) So i made another for the coolant bottle. Not much point in progress pics so heres the completed item.

The tube is 10mm OD, 8mm ID from bunnings and its bent using one of those hand held tubing benders plumbers use. PLEASE DO NOT USE COPPER OR BRASS TUBING. It'll make a battery basically and turn your engine and radiator into mush.

Lots of trial and error is needed when doing it. The final one is the third piece i had to make. Another little tip is to jot down an arrow in permanent marker in the direction the bend has to go, this makes it a bit easier to jig it up in the bender.

But none the less it now passes in between the radiator, forks and frame, allowing full lock and nothing touches anything else :) The grommets just stop the tube gouging at the steel bracket.

One unavoidable issue was the tube passes about 5mm away from the exhaust. Not sure if it will affect it any considering its just the overflow line, but i can keep an eye on it with the temperature gauge. Exhaust wrap is also a solution there if its a problem.

Everything packed into the front, I still have to remount the damper parallel across the forks like a GRC or DM just to neaten things up and the front end is all done once more. It was quite an effort to make everything fit without touching or binding on something else. Starting to look like a moto gp bike now! Just have to install the gyro sensors and electronics up the front and.... lol.

And with all the covers on. Looks pretty awesome IMHO (the only one that matters after all ;p)

Just have a couple of quick things to change before the next race ill be going to (probably in the ACT mid october) Like installing a smaller red water pump pulley that i think will help the running temps some (i also need the stock pulley for another project :P ), Put a metal fuel bowl on the carb so i can change jets easier and rejet it for some 110 octane race fuel i got given.

Pretty happy with it as things stand! Bring on the next race ;)

No more loose manifolds

2010-08-26T19:04:00.000-07:00

Ive mentioned it a few times but havent put any pictures up so here goes.

This is just a quick way of stopping the exhaust manifolds on water cooled bikes constantly shaking loose. I found that even with decent loctite the bolts would still loosen up eventually and getting the manifold on with the engine in the bike was the stuff of nightmares.

So with the tops cut off a pair of M6 stainless bolts i threaded the new studs into the exhaust manifold mounting holes making sure they bottomed out before tightening them up with some good grade loctite (see the post about inlet manifold studs for more details).

With that done the manifold slides easily over the studs and is held on with a pair of Nyloc nuts. its much easier getting a socket in there to do them up as well vs wrestling around with an allen key.

Added bonus in that the chance of stripping the hole out in the barrel is much less, and if the thread on the stud breaks you can just weld a bar onto the stud and twist it out (the heat of the welding will loosen up the loctite)

I havent had any temperature related problems with the nylocs yet but if i do there's plenty of alternatives like split beam locknuts and glenloch nuts amongst others.

Dellorto SHA air filter sleeve

2010-08-18T21:23:00.000-07:00

Sooo long time no update yet again. for that i apologise :)

Slowly getting the cag improved and back together again, so keep your eyes peeled for more updates on that front, but for now just a quick mod.

I've for the most part, failed in finding an air filter that fits the dellorto SHA properly. the closest ive come are 58mm diameter ones that you have to stretch over, and they slip off uber easy or a 60mm one that flat out doesnt fit at all.

For a while ive been just wrapping the outside in electrical tape then sliding the filter dodgily over that, but the fuel eats the tape away and the filter falls off. That is a slight problem.

So, doing the regular metal dumpster dive i found a nice piece of 70mm diameter aluminium tube. Perfect for making a sleeve to go over the dellorto to make the air filter fit.

Obvious size differences -

A few minutes on the lathe and the sleeve is done! Because the metal ring is so thin i cut it undersize then just tapped it on gently with a rubber mallet. It wont be coming off EVER. You can also see how its a lot longer then the shroud on the carb so the filter has more area to clamp on to. In fact its such a tight fit the hose clamp is barely needed :)

You can see the sandwhich of parts here, its only a tiny difference in size ~1mm but it makes such a huge difference.

Best give that carb a good clean too eh ;)

bling biatches$$$$

2010-06-27T23:33:00.000-07:00

So taking apart one of my cag motors for the 1059584v2.3th time, a common theme i noticed is that the washers behind the crank bolts are always bent in because the face of the clutch and flywheel arent flush with the end of the crank, so as the bolts are tightened up the washers crush inward.

I had a similar thing happen on the weapon shaft of my robot (i am a massive nerd indeed) So i made some plugs out of 2024 aluminium. They weigh the same but they are much more solid and dont bend + look pretty awesome.

So i spent 20 minutes out on the lathe and cranked out some similar ones for the crank of the cag engine out of a bit of mystery aluminium. I reckon they look pretty awesome :) and they do serve a bit of a usefull purpose because i can torque them down quite alot more then with washers. so good-o!

Studs tiem

2010-06-27T23:19:00.000-07:00

This seems to be a technique im employing more and more when it comes to pocket bikes, and that is to use threaded studs and nyloc nuts in place of bolts. To me it seems that its much easier to install the part over the studs especially with the engine in the bike and the added bonus of using nyloc nuts instead of expensive loctite + not having to wait for said loctite to cure. IMHO it makes it harder to strip any threads as well, and if you do its usually on the stud which you can weld a nut too and extract easy as.

So far ive done it on my elite motors exhaust manifold and its working great. The manifold hasnt loosened up at all since its been done vs the multiple times with standard bolts even with loctite so id consider it a success.

Next part of the engine to apply it to is the manifold of my chinese motor. Sometimes its handy to be able to take the reeds out of the bike and check them cause they are a consumable item but its usually a nightmare to do and get the bolts back in and lined up etc. not anymore :)

4 stainless steel bolts with the heads cut off, and then they are loctited into the holes.

Nice and easy to just slide the manifold and reed block over the studs without juggling around bolts. some nylocs go on top and then can be done up with a spanner from the side -

So that should make life a little easier :)

One piece into two piece cylinder head conversion

2010-06-21T00:47:00.000-07:00

So ive done a one piece barrel into two piece barrel conversion a couple of times now, and the bike is generally running much better as a result. But i realised a little while ago that the heads i had were for a 40cc barrel, not a 50cc, so the squish band was way too tight in some places and too large in others. So for the time being ive been using an ADA replica head which i dont like all that much in design.

Its too small in size and i dont see how it could radiate heat as well as the finned ones i have now. Soooo i decided to make the finned ones the same style as the ADA with the removable squish dome, allowing me to use the 50cc dome thats in the ada in the finned head. Id seen it done on a german forum so i figured it wouldnt be too hard. and you know the germans always make good stuff...

So out to the lathe and i did a bit of a dodgy to get the head mounted to the lathe. i just mounted it on the reverse side of my barrel jig with some extra long m6 bolts (the ones in the cag headkits funnily enough) and some m8 nuts as spacers. Ill make a jig if anyone else wants this job done but for a one off it worked.

First part is to drill out the center to 22.65mm which is the diameter of the squish dome. first using a 12mm drill bit:

Then a 19mm:

Now because i dont have a 22.65mm drill bit (if you do let me know ;p) the rest has to be bored out with a boring bar. Which is just a long lathe tool that can bore out internal diameters. i like these brazed carbide ones, cheap and effective.

The reason i havent cut the bolts down is because i need them to actually assemble the motor :P

After a couple of quick passes the diameter is spot on. This aluminium is so easy to machine. The chinese reclaimed coke can metal finally shows its benefits.

With that done the next job is to turn the face down of the head by 5mm (which is the thickness of the squish dome where it sits flat against the head). Didnt get a picture of that but im sure you can imagine :)

Next, a taper was turned into the face of the head to match the taper on the back of the squish dome. this has to be quite accurate so the two match up to allow a good transfer of heat between the dome and head.

Here ive set up the cross slide on the lathe at exactly 30 degrees. by advancing the cross slide in the taper can be cut.

Because of the long bolts holding it together i had to go into dodgy mode v2.0 and use a threading tool to cut the taper as it was the only thing i had that was long enough to clear them. thankfully the metal is so soft that it worked really well.

Taking the first cut:

Done. the finish isnt so great, but heat transfers better through rough surfaces anyway :P i think...

And the complete item. Now to test it out!

Better boost ports

2010-06-13T03:46:00.000-07:00

I did a blog a while ago on putting boost ports into a cag cylinder, so i wont go over that again. but these are a few of my latest barrels.

instead of just a flat top they're done with a ball nosed end mill so the charge is directed to the top of the barrel so it should work alot better then my current ones. They're also a little deeper in the cylinder wall so should flow a little better. Cheers to Nick for milling them in while my milling machines still getting fixed :)

Also had to window the piston to allow the charge to flow into the port itself, because of the design of the crankcases they cant flow around the piston like a standard water cooled engine. Less then ideal but better then nothing. You can see ive sanded the uneven finish off the top of the stock piston as well, i never got round to polishing it :P

So ill see how these ones go and then experiment with 3 boost ports, and an extra wide single boost port.

Making a spark plug mandrel

2010-06-11T01:01:00.000-07:00

Okay so this is more of a machining entry then a minimoto post, but its related so here goes.

To machine a head on a minimoto you need to be able to mount it up on the lathe. Thats quite difficult because they're quite intricate pieces with lots of wierd angles, and quite thin as well, so mounting them directly to the chuck or faceplate is generally out of the question.

Thus the only way to mount it up properly while keeping everything concentric is to make a threaded mandrel that will clamp in the chuck and the head threads onto it through the spark plug hole.

For the squish dome i made for the banshee i had used a turned down old spark plug, which while it did work and work quite well, was excedingly dodgy.

So out to the lathe and a piece of rusty old 16mm steel shaft was thrown in the 3 jaw and turned down. I just skimmed enough off the outside diameter to get rid of the rust and turned the end down to 13.80mm which is the major thread diameter.

I also had to make a slot at the end because my lathe doesnt have a thread chasing dial. If you want to know the reason why google it ;p

Below is a pic of the part ready to be threaded. you can see the threading tool which is specially ground to have the same angle as the thread itself. You could technically grind one yourself but they're really cheap to buy premade anyway..

Heres a brief video detailing the threading process without a threading dial, its much easier to understand with a video i think :)

The thread after the first cut. you can see it taking shape. The cut is about .25mm deep per pass. It seems any deeper and the finish is pretty terrible and you blunt the tool pretty quick.

And after a couple of passes heres the final part! Well technically not true, i accidentally put a gear on the lathe that had 6 teeth too many and the thread was marginally too big in pitch. ARGHHG. so i had to do it all over again. Having done it once it took about 10 minutes instead of an hour :P so all was well.

Now it can be mounted in the lathe and some heads shaved down. This is done to increase compression or correct port timing / squish. The run out is about .08mm when measured on the head itself which is pretty decent. although i think its actually perfect and the .08mm comes from the orginal machining.

The finish on the threads is pretty rough to be honest, even though it works just perfect and after threading it on and off a few times it cleaned right up. So i may have to have a bit more of a play around with threading.

Machining down skirt on a chinese barrel

2010-06-07T23:30:00.000-07:00

I thought the build for my 911 engine was going a little too smoothly with all the chinese parts in it, so it was a relief to finally run into a typical chinese part related problem. Hopefully this is the token problem done with :P

I got a Polini 50cc 5 port replica top end from danny at pocket racing bikes as well as a stock banshee cylinder to put on. I decided on the polini replica top end because the port timing is MUCH better (very close to the real deal polini) even though the banshee barrel is a little better in casting and the ports are cleaner but that can be fixed on the polini rep.

So the problem i ran into was the skirt at the bottom of the barrel was cast a little too thick (or not machined down one or the other) and wouldnt fit into the crankcases. Machining the cut out in the crankcases out would have been faster but i wanted to use a variety of barrels in the future, so the only option was to turn down the skirt on the barrel.

First i used my temporary jig (made from some nylon - going to remake a much more elaborate version out of 6061 soon) and 4 jaw chuck to hold it in the lathe. Dial indicator was also used and the runout was about .05mm or so which is as good as i could get it due to the jig being (soft) plastic. But that is still fine for this, as concentricity isnt totally essential.

Doing an interupted cut like this usually isnt a problem at all but the casting being quite thin and made from cast aluminium meant it was a concern that the skirts could snap off and then the barrel would be ruined. So i had to run the lathe at 200rpm (any faster and the whole thing would vibrate too much) and use a woefully slow feedrate, the enitre operation took about 2 hours. to remove the 1.5mm of metal.

Taking the first few cuts - depth of cut was about .175mm at maximum to lessen the risk of breaking the skirt off. i could have gone to about .25mm im pretty sure but considering the risk i was happy to be patient :)

Done! i did leave a little ~.3mm step at the bottom to save plowing the cutter into the base and gouging it, but the .5mm thick gasket means thats not a problem. Another bonus of doing this was it cleaned up the pretty daggy castings on the piston skirt. Looks like it could have been a polini in some other life haha! maybe..

Next, more cag engine work and assembling this 911 motor some more.

Trick to installing crankcase bearing

2010-06-07T23:13:00.000-07:00

So this is an old trick that most people know but theres always someone doing things the hard way :)

Just a video showing how to put in the crank bearings by heating the crankcases in the oven for 30 minutes at 150c then simply dropping the bearings in. the expansion of the aluminium allows for this to occur and saves any undue forces being put on the bearings during installation.

it also works on alot of things like getting siezed bolts out of aluminium blocks etc.

Correcting squish on one piece headkits

2010-06-02T23:17:00.000-07:00

Cags seem to be pretty big this year :P so ive been tinkering with them quite alot lately.

A new tracks opened up about 30 minutes from my place - http://www.kartatak.com.au/ so theres a new track to race the cag around. That means lots of testing and potential for modifications :P

The current engine in my cag is all bolt on modifications, with a stock standard 50cc top end no porting and stock squish level, which is funnily enough, without a gasket, over 2mm. Given this - the top end still goes pretty well, so with the proper squish it should be a pretty good piece.

On the two piece headkits getting the squish right is easy, you can just skim the top off and hold the barrel with a jig at the bottom (theres a picture of me doing this in an earlier post). however a one piece barrel is really hard to mount to the lathe. you cant keep clamp it in a chuck because theres nothing concentric to clamp too and even on the 4 jaw you cant get the base level.

The only thing i could think of was to make a press fit arbour. so i grabbed some 3003 aluminium (the super soft grade) and machined it down. I was pretty sure that just pressing the barrel onto the aluminium would rip the nicasil apart so i got an old throw away barrel and tried it.

It worked! even more surprising was that it didnt mark or gall the nicasil in the slightest. Heres a picture of the good barrel mounted up. the run out on the base of the barrel was somewhat scary in that my dial gauge didnt have enough scale to actually measure it. Seeing as though the arbour was machined to within .01mm TIR i know its the crap chinese machining.

So, next up was to make a custom lathe tool as i didnt have a right hand turning tool. Grinding your own from HSS is a good skill because you can make a tool for every situation, like this. You can see it in the bottom right of the picture below. There needed to be a relief on the front of the tool so it wouldnt crash into the barrel skirt.

And skimming the barrel down! I wasnt sure of the actual squish because i didnt have solder thick enough to measure it, so i had to take the barrel off and check periodically. That was done about 5 times, and the nicasil wasnt damaged through the entire process, so im well pleased that this works.

In the end i took about 2.5mm off the base of the barrel, because i wanted to use a gasket on the base (which is 0.6mm thick) and keep the squish around .7mm for now. Goes to show how rediculously off the chinese parts can be.

I also took the time to port out the exhaust port which was extremely small. i took it to 70% bore width of 30mm and heightened it an undisclosed amount, so ill see how that works at kart attak next time! and if it needs any more modification ill lower the squish some more and try again then move on to boost ports.

I may well refine this technique by adding a plastic plug on the end of the arbour that will fit all the way into the bore (the arbour now only goes in about 30mm) and make it impossibly to chip the nicasil.

Preparing crankcases for rebuild

2010-05-27T02:57:00.000-07:00

Just a quick update, For the chinese class 911 dreambike replica again.

Finally ordered all the engine parts to finish the bike off, as well as a new SAVA MA rear tyre (cheers to Darren from www.ozminimoto.com.au ) so time to start getting all the engine parts prepared for the rebuild.

First port of call is the crankcases. These are from a stock 911 rep motor and are basically identical internally to the polini ones so im happy to use them (im using the same on my elite bike). The factory uses gasket sealer on them so the gasket usually never comes off clean, so there is quite a bit of work involved to make the crankcase halves seal properly again without the need for sealant.

First is to give the cases a good clean to get the oil and grime off. i used a tub filled with diesel and a big paintbrush which works well for getting all the oil and clutch dust off.

I didnt get any before pics but the first thing i do is to scrape off the big chunks of gasket with a razor blade. The blade has to be held at a fair angle to stop it gouging into the aluminium.

Having done that the next step is to raid the kitchen for the scotchbrite.

The Scotchbright is good for taking all the baked on bits of gasket off that wont come off with the razor. They're quite gentle on the aluminium as well so you cant really remove enough metal with them to be of concern. I used the scotchbright with soapy water and scrub away. some of the harder baked on bits i had to hit with carb cleaner before scrubbing. One thing to take note of is you have to THOROUGHLY clean the cases out afterwards because the plastic fibres from the scotchbright will be everywhere and are going to go straight into the crank bearings if the cases arent clean.

But the end result is pretty good. These should now seal without any sealer which makes the next rebuild a pretty big nightmare. If they dont then the next job will be to make a mandrel to hold the cases so i can skim them flat in the lathe.

Cad design

2010-05-15T04:57:00.000-07:00

Bit of a digression from past posts but related none the less.

Cad (computer aided design) is pretty important in another hobby of mine (www.robowars.org) so i learnt it years and years ago out of neccesity almost. Thankfully it also comes in handy for designing mini moto parts and consequently sending them to the CNC machinist / waterjet / oxy / laser cutter for production

Heres a few ive been working on.

911 Footpegs. The originals are made from cast aluminium and they are extremely weak. i broke 3 sets on my first raceday. These will be made from 10mm aluminium CNC milled out so theyll be pretty damn strong. In the 911 the brackets also brace the main frame / swingarm area so extra strength here is welcome.

The top one is the final design.

Also a long term project ive been working on, i had a GP3 replica frame made out of aluminium by a chinese company years ago to replace my original steel one that was made like a pretzel. a couple of parts i wanted remade because they buggered the design of it up so i reverse engineered the parts that i had to change.

VS the real thing

The side panels - One of these i want to modify to accept the waterpump (like the Phantom minimoto or a GRC RSR)

Steering head - this part has to get modified because of the massive rake they build it around for some reason.

Last piece for now is a new Brake caliper bracket to hold a chinese caliper instead of a GRC one.

Happy to do any CAD reverse engineering or design of new parts for anyone :) can export to most formats DXF etc

KTM style clutch

2010-05-14T01:28:00.000-07:00

This is a bit of an ongoing project, and its not finished yet but worthy of a post all the same.

When i first started in the sport i had quite a few instances of BZM 2 shoe clutches tearing the linings off and burning up very quickly. Mostly due to misuse the first few times but the last pair of clutches just let go under barely any load at all. So i wanted to make a clutch that was fairly "idiot" proof and much more robust then the ones available at the time.

Since then new clutches like the 2A and the BZM delta (which get a bad rep but i like them, they work well for me being a slower rider) have come up which sort of answered my problems, but for the sake of do it yourself'ness (is that even a word?) i wanted to finish my home made one.

The design was shamelessly ripped off from Frank Giannini's which consists of KTM 50SX pro clutch shoes on a custom aluminium hub. I chose this style because the shoes are easy to buy locally at most dirtbike stores, and they were cheaper then the bzm ones at the time. The other main bonus was the clutch material covered nearly 360 degrees. So the hook up should be awesome. This is Gianninis original style.

A problem with this design however is that they use special cone washers to act as the clutch spring and using various stack shapes and thicknesses is how you set the engagement RPM. they also heat up and wear out after a few hours use and need to be replaced which isnt so good. So an ongoing part of the project has been to find a spring equivalent. The other change i made to gianninis design was to make the hub small enough so that the shoes can fit into a standard 80mm bell instead of the 82mm one they came with (i believe this was the case? maybe someone can educate me there) so thats one less job i had to do. boring out clutch bells is a nightmare.

Now making the clutch itself! Unfortunately i didnt take any photos of the process itself cause it was made at a mates house using his much more substantial machinery, but ill give a quick run down on how i did it anyway if any one cares for the process. first some pictures!

To make the piece i started out with a 60mm round of 2024 aircraft aluminium 12mm thick. it was bored for a 10mm center hole in the lathe. After this i then made a little jig to hold the round piece in the rotary table for machining. The hub is a sweat fit on to it and an m6 bolt clamps it solid.

After this was done i mounted the rotary table on the mill (all 50 something kilos of it) and clamped the jig in the 3 jaw chuck mounted on it. If you havent seen one before they look like this. it allows you to rotate your work piece accurately, usually to at least within a degree.

this allowed my to then accurately mill the 3 faces at 180 degrees to one another. i was able to get all 3 heights milled exactly the same via the use of the digital readout attached to the mill. they look like this - it allows the position of the cutting tool to be positioned within a thousandth of a millimeter.

with all 3 faces milled to size i was then able to drill the holes. i basically copied them off the original hub i already had so combined with the DRO it should have been easy.

EXCEPPPTTT there is only a readout on the Z axis (up and down) and X axis (side to side). the rotary table was mounted on the Y axis (front to back) which is the only way it would fit on the mill table because it was so huge. so i couldnt use it to drill the holes making the job alot more drawn out.

SO i had to do it the slow way which was putting the hub in the milling vice and manually lining it up 3 times to each 3 sides. to do so required the use of a dial indicator to make sure the flat on the clutch hub was perfectly level with the mill table. i was able to get it to 0.02mm. this is what a dial indicator looks like..

With the flat of the clutch hub level with the mill table i was then able to set the DRO up. So we know were to drill the holes in the hub we have to know where the edge of the hub itself is. To do that i should have used an edge finder - when it touches the work it lights up letting you know that it is positioned exactly at the edge of the part - the radius of the finder itself. handy!

Well unfortunately i couldnt find any batteries for it. so i had to hit up the interwebs at about 4am to find out what else i could do. fortunately the center finder kit also had an edge finder tool in it that worked great. i never knew what that bit was for until now!

With the DRO set i could then drill the holes for the clutch shoes. the center one is 5mm tapped to m6 for the clutch spring retaining bolts to sit in and the outside two are about 8.5mm for the 8mm pins in the shoes to sit in.

That was a bit of a nail biting moment because id been working on the thing for about 5 hours at that point. and if the holes didnt line up i had to start over. fortunately they all came out PERFECT. I LOVE DIGITAL READOUT. (in the healthy way of course)

The other three sides came out much quicker and all 3 came out equally perfect. Next job was to throw the hub back in the lathe and turn a bit off the face of it because it was a little thick and bore a recess in the front to allow the crank nut to sit further on the crank.

Finally the keyway! seems not many people know how they are made, so here it is. Its done using a large arbour (mechanical press) a small hub that fits inside the hole youve drilled (in our case 10mm) with a guide in it for the keyway cutter (the broach) and the keyway cutter itself (3mm wide for a 10mm hole).

The keyway cutter itself is tapered so it cuts deeper as its pushed through. There is a shim you put in behind the cutter to make the keyway a little deeper if neccessary. it wasnt needed here.

Wishing i took pictures of the build of it now, gawd dammit. but ah well. Definitely learnt alot through the making of it. Especially the usefulness of a DRO and rotary table. If i needed to make one again i could definitely make one start to finish in about 2 hours max instead of 7 or so. Providing there was a Y axis read out of course ;)

Next job to do on the clutch is get new cone washers and retaining bolts because mine are ruined. then work out how to replace the cone washers.

Main idea at this stage is to obtain some 8mm ID springs from somewhere (possibly a scooter) and then use a threaded stud instead of a bolt with a nylock nut on top to adjust the preload.

And thats all for now. Next time i mention it, this baby will be in my 911 and working :)

Next blog = hopefully some CNC parts.

New squish dome for the banshee

2010-05-10T22:21:00.000-07:00

The Banshee has been going really well as of late so no real updates on that.

However the banshee was lacking any decent RPMs since i changed the setup last time, although it picked up torque. Even though its a better setup it bugged me it just dropped 2000rpm so hopefully that can be retained with yet another configuration change.

Got a blank squish dome made by lisci racing from Bollins racing and ground out a HSS lathe tool blank into the shape of the combustion chamber from a bzm dome (thanks to Allan from bollins racing on that one too) and made a new dome from the blank followed by giving it a polish with some 800 grit wet and dry.

Wont give away what the squish and compression is but its allowed the port timing and compression to be adjusted so that hopefully the torque will remain and the revs will reappear :) hopefully i can quantify the change its made soon!

Making a one piece cag barrel a two piece

2010-05-10T22:04:00.000-07:00

Long time no update, Bikes have been working well so no real need to update until now :)

Seems cags are taking off in NSW with a few of the other elite racers getting them up and running so the class should be well under way soon. My cag has been going for a while and works well, but it still is running the stock one piece barrel with a woeful 8:1 compression and the timing is way off.

So to be competitive ill have to get a new motor going. about the only thing i have to do is make a new barrel / head combo as all the other parts from the old enging will swap straight over.

First i start with a much better barrel. I got a new one from Gray up in QLD. all the timings are actually pretty close to ideal and there isnt much to correct on it except the micro size exhaust port and the squish/compression area which isnt that great of a design.

to rectify the compression problem while keeping all the timings right the one piece design has to go. its going to be replaced with a seperate (much bigger) cylinder head and squish dome.

First job is to put the barrel in the jig which allows the barrel to be clamped in the lathe chuck. I only used the 3 jaw for now as there is nothing to indicate runoff from at this stage and accuracy isnt required for now.

Next the top of the barrel is hacksawed off. dawww look at the happy face.

From here its just a matter of progressively facing the barrel down until the brazed in compression area falls out. Took my time here because tenths of mm matter. Go too far and you can kiss this barrel goodbye.

All faced down to the correct height. My barrel is on the right. the one on the left is a premade chinese job. You can see that now i need to turn the top of the barrel down so the cylinder head can slip down over it as a press fit. The amount i need to turn down is 6.00mm in length and to a diameter of 24.88mm which is the size of the chinese cylinder head im using for now. Typical chinese tolerances :)

Now that the compression dome has been removed i have something concentric to measure from (the Cylinders bore) so i put the barrel and jig into the 4 jaw chuck which is much more accurate. You can see here that im using a dial gauge to read the "runout" (how many mm off center the bore is). I achieved 0.01mm of runout which is the limit of my gauge and pretty damn good for the kind of lathe i have. heres a video of it.

http://www.youtube.com/watch?v=Rd0RrZrS4Tg

With that centered the rest of the barrel was turned to size. I had to remove an extra set of fins on the barrel which i was hoping i wouldnt have to, but thats no big deal.

Done! and the cylinder head is a nice tight fit. When i get on to setting the squish and timing ill probably have to turn more off the cylinder height. so i left plenty of room to do that.

Heres the chinese cylinder on the left and mine on the right. couldnt ask for a better job then that :)

Next job will be to set all the timings, squish and compression level (i wont be posting those :P) and do any last machining before assembly.

There is going to be a flat top piston conversion in the works shortly so keep an eye out :)

Happy to convert one piece barrels to two pieces, drop me an email at Glen.M.R@gmail.com

Adding o ring grooves to banshee cylinder

2010-02-11T21:03:00.000-08:00

Just a quick job this time, machining some O ring grooves into the top of a banshee barrel.

From new they dont have this setup like 99% of the other watercooled engines, they use a 3 piece head gasket riveted together. This is likely to leak a lot of the time and also results in the engines squish band being a massive 1mm or so.

Its possible to drill out the rivets and split the head gaskets into thinner parts, however its not a very elegant solution and can still leak.

By machining some o ring grooves into the barrel its possible to use any kind of head on the barrel as well as reducing the possibility of leaks.

Anyway, first job is to make a jig to hold the barrel so it can be mounted in the lathe. This plastic makes for a nice quick way to make jigs (its actually an industrial chopping board - so its nylon). lathed down so the barrel skirt fits into the center snuggly and the outside is held by the 3 jaw chuck. The 4 m6 bolts are counterbored into the jig to clear the chuck jaws.

To begin with i used a threading tool to ensure the grooves where in the right position, then switched over to a 1/16th inch wide parting tool to finish the job. it came out really well! bit hard to see in this photo because of the flash.

Radiators and convinience

2010-01-27T02:56:00.000-08:00

Fresh off another practice day with a few new things tested and a few more modifications needed.

One thing i wanted to try was to paint the radiator matt black to see what effect it would have on the running temperature.

Its known a black radiator is more effective at transferring its heat energy to the atmosphere when there is no air moving through it due to the colours higher emmisivity and absorbtivity. see these links for info

http://en.wikipedia.org/wiki/Thermal_radiation

http://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_radiation

In practice things rarely go 100% according to theory and i was worried the paint might make a barrier and stop effective heat transfer. Thus only way to check is to test it.

So here it is. nicely painted matt black radiator. this one is a bit ruined so if it didnt work it needed replacing anyway!

Out on the track the temp was about 30-35 so it was roughly the same as the last race day i tested the system at. After the radiator was bled it read a steady 70c through 20 laps which is identical to last time, however i was riding almost 4 seconds a lap faster then last time so its ever so slightly better. Not much but every degree helps.

Where it did make a large difference though as predicted by the theory is when the bike was at rest and shut off ala in the pits. It cooled down from 70c to roughly ambient in 15 minutes flat which is about half the time it used to take.

So the black radiator is a success!

Another great tip i got off Chris aka the claw was to put an angle spacer under the top radiator mounting bolts to angle the radiator fowards slightly. This lets you have more room to remove the spark plug which in a banshee is a complete nightmare of a job. especially when the bike is still hot.

Plenty of room now :) Spacing the radiator away from the exhaust manifold should help a tiny amount as well, it was touching the bracket before which isnt good.

Timing transponder mount

2010-01-27T02:37:00.000-08:00

Just back from a practice day down at wollongong. Very succesful :) knocked 1.5 seconds off my best time down to 36.4 which is mixing it up with the back markers. so couldnt be happier about that.

All the bikes worked well but it was a little annoying finding room for the timing transponder. they are pretty big (relatively speaking compared to a pocket bike) so finding room for them so they wont get in the way is tricky. so i made a solid mount for them

A couple of other guys at the track use this setup and it works well so i did the same. Its a piece of 28x28 x 1mm wall aluminium box section with two 19mm slots milled in each side then the original brake caliper mounting holes hold it on and two m3 stainless bolts hold the plastic transponder holder in. works well! weight nothing. all good :)

Cag race motor number 2

2010-01-20T20:32:00.000-08:00

After a really successful practice day down at wollongong city raceway with the cag its time for a 2nd test motor. Ill be contesting the aircooled class this year because the elites are too expensive now ive gone back to tafe (cnc machining, should be fun!) and i need the experience on a slower bike anyway.

The current motor im using is very stock in regards to cylinder squish (its about 1mm which is very high), it has no boost port and the exhaust port is still stock size. The modifications to it are mostly bolt on so it should remain reliable for the season altho down on power compared to the new one.

This motor should be very high powered and high strung. So i pulled out a few very old and worn out barrels to test a few techniques ill be using to make it before i ruin the genuine article :)

First part to be modified is the reed cage and reed valve. These engines introduce the fuel air mix into the engine via a flexible fibreglass/tin/carbonfibre sheet known as a reed valve. The bikes come stock with a thin tin reed that flutters badly at high RPM and just doesnt work well at all. The aperture is also very small so the air flow is heavily restricted as you can see. To get more power the engine needs more air mix!.

Milling the center bar out and opening the cage by about 3mm on the top 1mm on the bottom and 2mm on each side increases the flow rate potential up by almost double. You just need to be careful you dont ruin the sealing rubber on the sealing side of the reed cage.

To replace the stock tin reed im using a BZM .45mm thick fibreglass reed. This will allow the engine to rev much higher due to the reed being stiffer. The thick fibreglass ones work well. Ive found they allow the same revs as the carbon ones (which are generally regarded as better in watercooled engines) but give more bottom end. That and they are much cheaper!

Ive detailed the work on boost ports in a previous entry so i wont go into it here, aside from saying it will be shaped a little different from before.

The biggest difference from my other engines will be the main transfer ports will recieve some attention. Now im using a huge 16mm carburettor compared to the 12mm stock one and the reeds are modified the rest of the engine needs to flow an equal amount more.

The stock ports are pretty small and they arent shaped well at all. To aid in schnurle loop scavenging (look it up on google) and make the engine work more efficiently i enlarged and reshaped them with a ball nosed end mill to look like such. Excuse the finish, it was done fairly rough to see if it would work. The actual engine will use a much less agressive feed so the finish will be heaps better.

This directs air up towards the combustion chamber and away from the exhaust port before looping it back out the exhaust port due to the radiused port roof compared to the old flat one that just directed the flow into the center of the engine due to the old ports having a flat roof.

Next job is to port the crankcases out equally. They will be seriously modified so i will document that soon :)

Enjoy

custom chain guard

2010-01-16T01:21:00.000-08:00

After the clutch was all done and tested i decided to give the Cag a bit of a streamlined look. It had a big aluminium sheet on it to begin with which was definitely effective in stopping your foot going into the chain, but it was pretty big (ive got pretty small feet anyway haha) and took away from the sleek minimalist look of the bike.

The original -

After milling it down to size and putting some lightening pockets into it -

Definitely gives it that cut down sleek look im after. Its the small things that make a big difference!

New Clutch setup for cag

2010-01-14T00:16:00.000-08:00

The Cag is the most basic cheap minimoto you can get and the quality is well.. you get what you pay for.

So after a recent power increase to the motor i wanted to ensure the rest of the drive would work in a reliable fashion. so the clutch setup was modified.

Initially i installed the clutch off a banshee SHO to handle the power (the banshees are rated at 10.5hp which is much more then the cags put out). The bonus being they are adjustable so the engagement rpm can be set much higher then the standard cag clutches which effectively provides more off the line power.

The next part in the drivetrain is the clutch bell and housing. this transfers the drive from the clutch itself to the sprocket / rear wheel. the standard chinese items are fairly terrible in regard to they cant dissappate much heat and the stock bell is horribly out of round + made from very thin material.

To begin with i modified the stock housing by milling out some superfluous material around the edges and also milled out large sections from the centers to help the bell ventilate heat better. the inside has cast ridges so its still more then strong enough.

Stock housing is on the right and the modified one is in the center. Polini replica housing is on the left. The polini replica was upgraded to a different setup so i used most of the internals from it in this build.

You can also see the bell is slightly wider so it covers the entire clutch itself. which the stock one didnt do..

Next i needed to change the polini replica clutch bell - which is much better made with thicker material and substantialy more concentric :) To do this required a new bearing that has the same outside diameter but a slightly larger inside diameter. Removing the large circlip allows the bearing to be pushed out and replaced.

Because the polini replica clutch bell is a little bit larger in outside diameter then the old one (you can see the difference in the above pics) .5mm is required to be machined off. i did this on the lathe. while i was at it i also trued up the face. the rest was okay.

With the bell nicely trued clutch wear will be massively reduced. Thats good considering the rarity of the banshee clutches!

The center bore was also retapped to m8 x 1.25 to accept standard BZM sprockets. The chinese ones are notoriously crap.

A spacer was needed to space the bell away from the housing itself (i stole one from my old zocchi housing that didnt use it) and a section was milled off the front of the housing to stop the chain rubbing. Also seen in the picture is the custom roller i made so the chain will clear the swingarm, it used to rub horribly.

All done and ready to go! This setup should handle any level of power i build the motor to. and all with old parts i had laying around

Fuel line and filter setup

2009-11-29T21:35:00.000-08:00

One of the most critical things for the reliability and performance of your mini moto is to make sure its getting consistant and plenty of fuel flow into the carb. Unless you have that you will NEVER get your bike to run smoothly or properly.

With a poor fuel supply you can experience problems like cutting out after a few minutes of running, overly rich or lean jetting (maybe even seizure if your unlucky enough) and difficulty starting the bike.

The main cause is usually with the entire fuel system on the stock chinese bikes. The rubber/plastic fuel line used isnt particularly fuel safe and degrades really fast as does the stock paper fuel filter because of the 2 stroke oil. Take it off and throw the lot in the bin straight away. Retaining them WILL cause problems and the cost of replacing it all is $20 using the best parts available.

ANNNDDDD heres one i prepared earlier :) This off my pro cag using an SHA style carb. but the setup is still the same. As you see it in the picture is ideal. The run from the fuel tank to the carb is downhill with no loops or kinks which is what i usually see on a lot of bikes And the fuel filter is close to horizontal. if its vertical air bubbles can build up inside it and cut off the flow.

Also make sure that the filter is BEFORE the fuel tap. It takes a while for the vibrations of the bike to work out the air bubbles inside the filter, so if you have the filter after the fuel tap youll always have air in there. Bikes set up like that are always very hard to start.

An extra quality fuel tap is also a good idea. The stock CAG type carbs come with a fuel tap built into the carb. You should drill a hole straight through the fuel tap (remove it from the carb of course) and remove the rubber button inside - replacing the outer part with the tap on it with a blank piece of metal and gasket paper.

Make sure its easy to get too as well, and that the filter is easily visible to see if you still have fuel. its surprising how often you get caught out by that :P

How to - adjusting chinese style cable brakes

2009-11-29T19:47:00.000-08:00

Sorry for the lack of updates, Been flat out with other non bike related projects in the last week, but back to the bikes.

Adjusting the brakes is a fact of life when it comes to owning a chinese mini moto, you have to do it at least once so you may as well do it properly instead of whining about poor brakes and feel for the life of the bike. This guide pertains mainly to the single front brake bikes. Most come with two disks on the front that you should get rid of asap. They are next to impossible to adjust to be equal and dont work that much better then the single disk anyway.

First thing i always do for a racing bike is to purchase some thinner cables. the stock ones are really thick and you dont get a decent feel out of them. The GRC and blata made cables are perfect. If you dont plan on racing then the stockers will do you just fine.

Next is to adjust the cable adjusters on the brake cables themselves. There needs to be quite alot of adjustment in them as your cables will stretch over time. So wind them in all the way then back out two full turns. This is how mine look after having been set. As the cable stretches the free play in the brake lever will become greater, so you just wind out the adjuster to remove the slack.

Nearly there, next install the cable and route it in a way that it isnt excessively kinked and it isnt rubbing on anything sharp that will break or abrade the cable. make especially sure it isnt touching the exhaust. The cable should take the smoothest and least curved and kinked path to the caliper.

And last but not least we get to the brake caliper. First loosen the lock nut on the brake pad adjustment screw (The grub screw with the nut over it at the base of the brake arm) and wind out the adjuster a few turns.

Then install your brake cable. Be extra sure you dont fray the end of the cable! otherwise it will look ugly and be a bastard to take off and reinstall. I always solder the ends up with an 80w soldering iron to stop that. You can buy crimp on cable ends as well and some people heatshrink the end, but that never worked too well in my experience.

After that, Set the brake arm to be perpendicular with the "eyelet" (the little knob, the outer part of the cable rests against) and then let it fall back about another 10-20 degrees. How you see it in the picture is about perfect. Tighten up the bolt on the end of the brake arm making sure you dont kink the end of the cable in the process.

last thing you have to do is wind in the grub screw until the brakes operate how you like. That is largely personal preference but i like mine to have about 5mm of free play in the lever and be set quite firm. Test the brakes by spinning the wheel and pulling the lever with 2 fingers. it should lock solid and you shouldnt be able to move the wheel by hand.

tighten up the locking nut and your all done! Enjoy :)

Keep checking back, ill be finishing off the pro cag build and finishing off the pro-chinese class dreambike as well as showing off a few new parts that havent been used before + giving a little review on them. It should be good!

Preparing the pro class cag

2009-11-16T01:36:00.000-08:00

With all this work done on the motors obviously i need a bike for them to go in! So heres a bit of progress on the bike. It's going in the pro cag class that is basically anything goes as long as the chassis is a cag. The goal of the bike is to make it as close to the banshee sho in terms of geometry and riding position so i can ride both without having to change the way i ride the bike and also to make the stock cag handle better.

So the bike, its a typical cag chassis but its made from thicker wall tube then most and the welds are pretty good. it also has all the bolt holes for the motor mounts drilled (most only have 4 of them not 5). There was only few modifications done. The first was to box a part of the seat unit frame so a fatboy exhaust could fit on without fouling on the frame.

Also added an extra tube to cross brace the swingarm. the tube is only 2mm wall so its very light and has made the swingarm infinitely stronger.

Next up was a mounting tab for the fuel tap. You should drain the carb out if you plan on storing the bike for a while so the fuel doesn't varnish up the insides of the carburettor. The easiest way is to add a fuel tap and just turn it off then run the bike for a little to use up the remaining fuel. This is just a standard mower part. Mounted in a convenient place :)

Trying to reach around and fumble with nuts and bolts to put the fairings on is a bugger off a job. so tack welding some flange nuts on the other side of the fairing mount fixed that.

The bike came with some very sturdy footpeg brackets, but they where a little bit too foward for racing, and a bit heavy, so i took them off and replaced them with these ones. made from 10mm steel but very minimalist, so much lighter. They match the position of the banshee pegs perfectly.

the stock brakes are pretty terrible. so i converted them over to use standard banshee/911 type brakes, so i can use the same brakes on all my bikes. here is the adjustable bracket for them

Last addition for the frame is the chain roller. Stock, the chain rubs on the frame and chain guard bracket badly. so this little piece made from nylon and with two bearings in it works great. As you can see its used and works great :)

Last job for the time being was to repair the rim i was given. The terrible chinese phillips head bolts broke off instantly with the slightest pressure on them. and flush with the rim. Rather then wrestle with the tattered remnants i decided to just redrill them on the other side. Putting the mill into action..

A lick of paint, a pair of new steering head bearings and the frame itself is ready!

Total weight as you see it is 7.1kg which is great! heavier then a samurai type Cag but at least it wont fall apart underneath me :)

Lightened air cooled flywheel

2009-11-13T07:07:00.000-08:00

Following on from the post below, The next item up for modification and extensive testing is the flywheel.

On these aircooled engines the original source of air to cool them down when they were being used as agricultural engines was from the finned flywheel itself that draws air in from holes in the pullstart housing and ducts it up to the finned cylinder cooling it somewhat.

On our race bikes for the most part they are moving, and at a decent speed. so they dont need quite so much cooling as they once did. The original units are also heavy and have a huge amount air resistance when turning at 9000rpm not to mention they are often outrageously off balance from new.

The original type is on the left. it weighs in at 320 grams.

By lightening the flywheel the engine can rev much more easily and theoretically rev to a higher peak RPM. taking some load off the crank is also good for reliabilty.

On the right of the picture above is a standard performance part made in china as well. this one has had some of the fins milled flat and the edges scalloped. Its quite a bit lighter then the stock one and has much less air resistance while still maintaining its cooling function. However ive found these to be out of balance just as often as the stock ones are.

After a bit of experimenting about i found that the vast majority of the inbalance comes from the edge of the "disk" and the tips of the fins where the casting variations are greatest. So simply lathing the outer diameter down and thinning the fins length wise brought the flywheel into almost perfect balance with no secondary balancing required.

experimenting showed that there was almost no difference in measured operating temperature after a 20 minute ride between the original, 1/2 length fins and 1/3rd length fins, while the engine pickup and peaks revs was notably better with the 1/3rd length version. It is also lighter by some 20 grams over the others and quite a bit more over the chinese performance version.

Here is a complete one. it weighs in at 260 grams vs 320 of the original.

Also tested was a finless flywheel that weighed in at a tiny 230 grams that works better yet again. HOWEVER it will overheat the engine to dangerous levels if left to idle for 1 minute or more and it is extremely sensitive to jetting. even a little off will result in a seizure. so as such the type in the picture above will be the flywheel supplied in my engines.

If you want your flywheel machined to similar specs or want to purchase one new contact me at Glen.M.R@gmail.com for more info.

Boost porting cylinders

2009-11-13T06:40:00.000-08:00

Okay so lately ive been working on some improvements to the ever popular 40-50cc chinese air cooled cag motors. This is the first of many mods that will be in my finished race engines.

As they roll out of the factories in quangzho in their millions they are an okay unit. Reliable in operation but wildly varied in final tolerances and power. Usually they supply about 2-3hp and top out at about 8000-9000rpm

The main thing to remember about these engines as that they are based largely on an agricultural engine. So they never needed to be particularly powerful to begin with and were optimised to run reliably at a certain rpm for an extended period of time - pretty well the opposite to what we want in our race bikes - so the transfer port setup and induction setup isnt particularly suited to generating huge revs and power. Time to fix that!

probably the best thing we can do on an otherwise stock cylinder for power is to add whats known as a boost port. A boost port is a third transfer passage for air charge to enter the combustion chamber in combination with the two main transfer ports. Basically it helps scavenge the back of the cylinder and provites better charge purity = better power. roughly 10 - 20% plus allowing more revs.

I started off with a stock two piece head kit from HK motos as the prototype for testing because it already came with a single boost port added which will be the best for piston ring life (this type of port setup is rough on the piston rings so you dont want to run too many boost ports). As you can see it is all but useless.

The depth of the port is less then 1mm so the air flow is through it will be next to zero, and the height of the boost port is totally insufficient. With the piston at bottom dead center the port isnt even uncovered.

Easily fixed with the mill however! this one has been bored to the correct depth with an end mill and to the appropriate height. You will notice ive left the top of the port roof flat for now as i intend on comparing the power difference between having it flat and having it angled. The angled roof will obviously be better but i am curious to see just how large the difference will be! The height of the boost port itself is also another item up for testing.

4 Barrels are now complete with different port secifications so i will test all on the same engine to find which works best and get the complete engine dyno'd and post the results. stay tuned!

Should be up for sale in the near future in 2 piece and single piece guise.

X9 steering modification and some carb tuning

2009-11-04T23:24:00.000-08:00

So getting the X9 rideable has been a priority so heres the final work that was done to get it to this stage.

First job was a new battery mount. the original was well, non existant, so i fabricated this one up from some 3mm aluminium and an old gudgeon pin i had laying about that was conviniently sized. Just a simple clamp arrangement bolted down with 2x M6 bolts to keep the battery in place stopping it from falling into the frame rails and shorting out. TRUST ME you dont want one of these things to short out.

Steering bearings were equally non existant as well. half the balls were missing in the lower one and none were in the top bearing.. a brand new set of quality bmx bike ones (they are interchangeable) courtesy of blackmans bicycles with some heavy duty grease made the steering smooth as.

The setup was further modified by using a large m8 bolt that passed through both the triple trees and clamped them both together with a custom made aluminium boss kept things spaced apart properly. Definitely solid!

With that sorted a good thrashing was in order. the bike went fairly good considering its so heavy and the engine is so small. The jetting was well off however as you had to slowly wind the throttle on to prevent it cutting out, no doubt because of the filthy state of the carb that had been run with no air filter.

As it turned out when i pulled it apart to clean it, the atomizer tube was crushed by the main jet being screwed in way too far under serious force and all the atomizer holes squashed closed. The carbs being so cheap (less then 30 dollars with postage) i just bought a whole new one plus a foam air filter. If you run them without a filter there is a risk small particles can flow into the tiny idle passages and so forth and you will be trying to chase down the problem forever. at this cost it was sensible to just replace the whole thing.

Jetting was pretty good from stock. a quick adjustment of idle speed and the air screw (that meters the idle mixture) and it took off well from a stand still, however at mid to full throttle it would die. Dropping the needle clip one position to richen the mixture fixed that issue. The bike now ran great along with a new NGK spark plug.

Plenty of fun to ride around because the riding position is much more akin to a full size bike then a mini moto and dragging the knee about in the car park is pretty easy, even if the bike is horribly unstable and prone to tank slappers. definitely installing some kind of steering damper!! For a 50cc 4 stroke it definitely has a fair bit of low down torque and revs out well. the biggest let down is the lack of any gearbox so the top speed is pretty slow. in the region of 50kmh.

Last job done on the bike was to add a head/valve breather. They are supposed to help relieve the head of built up pressure (allowing it to pick up revs quicker and lengthen the life of the top end parts) as its argued the crankcase breather is insufficient. Now there is a lot of debate as to whether these actually provide a difference. The general consensus being that on large capacity high revving engines they do but are hardly worth the effort on low power and capacity motors. I figured it was only a 5 minute job so here's mine!

Personally i felt no difference to performance and no real flow out of the breather, but you dont know if you dont try!

Next up is a new muffler a bit of work on the dash board + rewiring plus some fairing modifications in the future.

Mega cheap coolant temperature gauge

2009-11-03T17:38:00.000-08:00

Often in the elite class of racing the prices for parts are pretty steep. But that doesn't mean you cant get around that and with a bit of tinkering and ingenuity, get the same result for a heck of alot less money!

The aim was to make an accurate and cheap coolant temperature gauge for my elite class liquid cooled mini moto. These are very handy items as they can help you assess whether certain modifications are causing the bike to run too hot or if that giant $200 billet water pump actually made a difference amongst other things. 2 strokes are very sensitive to coolant temperature as well and run best around 65 degrees so its handy for getting maximum power.

The device i originally wanted was an awesome device called a mychron 4, but at nearly $600 that was way out of the question. I got to thinking about using an aquarium digital thermometer but most only advertised a maximum temperature of about 80 degrees at best and with an update time of 50 seconds or more which is not very useful for what i wanted to do.

I got onto an online store a while later called http://www.dealextreme.com/ and while buying other things saw they had a few thermometers for $3.29. so i grabbed a handful of them with the intention of hacking them into a working coolant temp gauge.

These are the ones i used - http://www.dealextreme.com/details.dx/sku.15553

Here they are! the temperature probe is just a thermistor epoxied into the metal tube you see in the top left of the picture.

After some experimenting it was found that despite the claims of the manufacturer they actually read all the way up to 120 degrees before reading error on the LCD as well as being only 1 to 2 degrees off an expensive brand name thermometer. Unfortunately the update time of the screen was indeed about 50 seconds apart.

On closer inspection there are blank solder pads with no components on them labelled SW1 SW2 etc.. with a bit of experimentation it was found you could change the display from degrees F to C and if you joined the two pads labelled SW3 together the update time was reduced to only 7 seconds. That was good enough for me!

So now i had a digital thermometer that read up to 120 degrees C and updated every 7 seconds. perfect for the bike. Next an adaptor had to be made to position the sensor in the coolant stream to read accurately.

In the picture below is the semi complete item. its a 2024 aluminium rod turned down to have 10mm ends for the hose with a large center section and a bolt tapped in sideways. there is a hole drilled straight through the center of the bolt (i ended up using a different bolt ill explain why later). The sensor has to be placed in between the cylinder head and the radiator as that is where coolant is hottest!

The sensor from the thermometer was placed into the hollow bolt and some metal epoxy was used to fill in the back of the hole and make it water tight. i used a socket head bolt instead of the hex one in the above picture so the epoxy could flow into the middle and seal better. The sensor is flush with the outer diameter of the adaptor so that the coolant flow isn't inhibited in any way.

some permanent loctite kept things water tight and reduced the risk of it every vibrating loose.

and here is the complete project! excuse the state of the bike in the picture. had a few other projects going on that ill post up soon ;)

The unit got its first test last weekend at Wollongong city race way and worked absolutely flawlessly. No leaks and accurate reading all day. The hottest i managed to get the bike too was 74 degrees in the hottest part of the day and 68 degrees in the night time race. So the coolant setup is pretty well ideal. ill look at ways to get another 5 degrees off and that is one job done.

If there is enough interest i will make a few of these including the adaptors and all the mods to the thermometer for $50 each. so drop me an email at Glen.M.R@gmail.com

50cc 4 stroke tear down and inspection

2009-11-03T16:58:00.000-08:00

The weather isnt too good today so it's a good opportunity to tear down the 4 stroke in the X9 mid bike.

Here's a few pictures of the tear down. i didn't get any of the re-assembly but its much the same as the assembly ;)

Okay so first thing to come off is the right side engine cover. What you see here is the automatic clutch on the right and the main drive gear to the left and behind. The clutch itself is the same as the semi automatic type without a few internal parts found on the CT110 (it was originally designed by jawa fyi :P). Flat plate type and centrifugal in operation. Its a robust piece and showed no signs of wear at all on this engine. You can buy uprated springs for them as well as performance clutch plates to raise the engagement rpm and give it the effect of more power.

These engines have a very very basic oil filter if you could call it that. Just a small screen to filter out any large bits of flotsam. There was a tiny bit in there but nothing to worry about. gave that a clean and back in it goes..

Onto the left side. Ive removed the starter motor which sits in the casting up the top and drives a sprocket with a one way bearing in it just behind the big brass rotor. that was all up to scratch.

The large brass rotor is the flywheel and it also has a series of large magnets on its inner side and a small one on its outside. The small outside one is the trigger magnet that controls when to fire the spark plug and the inside ones generate power for the lights and battery charge circuit.

There are performance flywheels available that cut down the flywheel to a very small weight and size (called an inner rotor or outer rotor kit) so the engine can pick up revs faster which would be a good bonus on an application like this but in the interests of cost the stock setup is just fine.

Also visible on the right side is the (slight rusty) output shaft. unlike most motors of this kind this one has an extended shaft making it very tricky to swap over to another type. To put a bigger motor in you have use this shaft and machine the circlip grooves into it then install it in the new motor.

Next up is the stator and left side cover. After testing the resistance it was all good. Just had to resolder one wire that looked a little suspect in its connection. The two large coils in the center generate the power for the lights and battery as described earlier. The wires go to the rectifier to be converted to DC.

The small black box on the top right is the trigger. Also as described before it sends the signal to fire the spark plug to the cdi/coil. All of that was fine so onto the cylinder!

This is the top of the top of the engine looking into the barrel with the cylinder head removed. The cam chain is on the right side and the oil supply + drain are on the bottom (the rubber o rings) which were perished and needed replacement. This is a 50cc "short" barrel which is quite rare, as many are actually 70 or 88cc engines labeled as 50cc to get around import restrictions.

The piston itself. it looked in fairly good condition especially the rings (good enough to get it running again anyway) but it had cold seized on the top side a little bit. That is when the engine is run too hard from cold cause a seizure - so always warm up your engine thoroughly! Thankfully the bore wasn't marked so it was okay to use again after cleaning all the carbon off the piston and giving it a quick polish.

And the part where the power is made! the cylinder head. this one was in good condition. the valve seals and seats where really good and the head wasn't warped. so cleaning the valves and combustion area up saw this piece ready to re-use. You can see how tiny these valves are compared to my thumb. Big valve, 3 valve and 4 valve conversions are available.

Top of the cylinder head and camshaft + rockers. all the bearings looked great as well as the camshaft. The rocker setup isnt as ideal as the shim over bucket but works fine on a 50cc chinese made engine ;) it allows for very quick valve adjustment even though they need to be done more often as a result. Camshaft upgrades + valve spring upgrades are available.

This is the valve adjustment part of the cylinder head. To adjust the valves you just undo the lock nut and turn the center screw in while putting a feeler gauge in between the valve and screw. the engine MUST be on top dead center compression stroke otherwise it wont be right. I find .1mm and .15mm on the intake and exhaust respectively to be the best.

There is a great tutorial on youtube if you search for adjusting valves honda 50cc.

So there you have it! assembly was just the reverse of this, only things to note are that the gasket surfaces are very thoroughly cleaned with gasket remover to ensure a perfect sealing surface surface and all important bolts are torqued down to specs.

Some repsol 10w-40 motorbike oil and a new gasket kit and the job was done for less then $30.

Pro china class bike build 1

2009-11-03T04:13:00.000-08:00

Last post for the day! I had a bit of time left after the other two bikes were worked on to put in a bit of time on one of my team bikes.

This particular one is for the Pro chinese class. that means it has to be a chinese made mini moto but regulations regarding the engine are fairly open. that means certain parts like the crankcases and engine barrel must be chinese made (but can be modified) where as the bolt on bits like exhausts, carbs etc can be European or genuine brand items.

The bike im using as a starting point is a ZX-1 Taipan which is a Chinese made replica of a polini 911 dreambike. I chose it A) because i own one already and B) its the lightest water cooled bike you can get. So with the limited horsepower provided by the chinese based engine a light bike is a big bonus!

This bike already had a set of good quality banshee SHO wheels on it as opposed to the standard cag like wheels they come with, which is great from a strength perspective - unfortunately they don't accommodate a rear wheel driven water pump pulley like the stock one so some modifications had to be done.

The water pump pulley itself was from a DM mini moto and it mounts as a tight press fit behind the sprocket on a circular part of the hub. This wheel however had a tapered hub with 3 "stubs" on it so the pulley wouldn't fit at all. The solution was to jig it up in the lathe carefully and turn a flat area on the hub upon which the pulley could sit.

Here the machining is nearly done. The metal was getting quite thin near the bolt holes so i also took some metal out of the inside of the pulley as well and in the end it all came out great. you can see the flat areas where the pulley sits on in this picture.

And it fits! plenty tight too. Some pulleys mount by bolting to the sprocket itself, but this way makes it faster to change the sprockets at a race as it stays with the hub. To lock it on even tighter the pulley sits a thou or two above the surface (an extremely tiny amount) and the sprocket clamps it on tight.

Below you can see the finished product with everything bolted up. One problem i had when i put it together was that the wheel sat too far to the left because of the hub offset which made the pulleys and sprocket run misaligned. Remaking the spacers out of 2024 aluminium to replace the steel items (every bit counts!) and milling down the brake bracket made everything line up.

All it needs is a tire and new brake cable and the rear end is done!

Thats it for today. thanks. if you have any questions at all email me at Glen.M.R@gmail.com

Samurai Cag overhaul

2009-11-03T03:50:00.001-08:00

This is another of the three repair bikes.

It's a Samurai type cag which are probably one of the worse ones you can get quality wise. the welding is especially bad and they are quite frustrating to work on compared to the other kinds due to some awkwardly placed bracketry! They are however the lightest type of Cag so perhaps good for the hardcore racer ;)

Typical of many Samurai's a few parts of the frame needed rewelding. the rear brake caliper bracket had sheared off a few mm above the weld (thats how bad the metal is) as had the top end mount. Both were remade from 3mm mild steel and TIG welded back on.

Another problem i see on alot of these bikes are seized chain links. Often caused by not using a good quality chain lube (or none at all) but also - and in this case -parts of the frame grinding on the chain. the chain cover bracket was actually grinding on the bottom of the chain. the cover is practically useless on these bikes so it was removed along with the offending bracket. Good quality BZM chain and regular lubrication fixes that issue.

The saving grace of these samurai bikes is that the engines are pretty good and generally bulletproof when left stock. They are just not highly tuned enough to kill themselves save a dodgy chinese bearing here and there.

This was a good one as it came with a 50cc engine from new where as most are 39cc. You can tell by the bore measurement (44mm vs 40mm) and also the bottom fins on the barrel dont join all the way around on the 50cc versions.

For a stock engine it ran surprisingly well. Upon dis-assembly everything was great inside so i put it back together only one piston ring this time (the two ring design is a relic from the motors original use in agricultural tools - it serves no real purpose that the single ring cannot do in this application) and also lowered the squish down to .5mm from over 1mm by using good quality liquid gasket and carefully milling the crankcases and bottom of the barrel flat. This part is essential or you will forever have air leaks!

The jetting was spot on from stock aside from lowering the clip down on the needle to make it a tad richer.

The performance increase was very noticeable after even this small FREE modification. The customer was very surprised at how much better it went considering it was all using the same parts! Just goes to show how important port timing is on 2 stroke engines.

The obligatory replacement of the very poor chinese parts like the spark plug, footpegs and fuel line + filter saw this job done.

*pics to be added soon*

X9 mid bike

2009-11-03T03:25:00.000-08:00

Alright this is one of three bikes to get repaired. Unfortunately it required alot more money then it was worth to repair to a decent reliable state, so the owner offered to trade the bike for the labour on the other 2 bikes. So it is now part of the GR fleet. Here's a few pictures of it when it first arrived

The eventual plan is to convert this one into an electric bike using a MARS "brushless etek"setup i purchased long ago.

In the mean time to get the rolling chassis and other associated gear up to scratch i decided to get the motor going to a somewhat running state so i can assess how it handles and what needs to be done elsewhere on the bike.

The bike was missing the starter solenoid and the battery was really flat but aside from that the engine appeared to be complete. A temporary 30A solenoid from a car stood in for the original solenoid and after cleaning the carb out thoroughly and replacing the dead 7ah lead acid battery it still wouldn't crank.

further inspection showed the spring inside the starter motor had been replaced at some stage with a pen spring. so a 100w scooter motor spring was added (they are basically identical) and after a couple of cranks it popped into life.

After a quick ride it was obvious the steering bearings were totally shot and i nearly high sided it at 20kmh after the steering jammed solid. so next is to replace the steering bearings and overhaul the steering setup and give the motor a quick freshen up. The motor also had a seriously bad surging problem and refused to work at wide open throttle unless the throttle was slowly wound on.

so next is the motor tear down and rebuild, replacing the steering bearings and redoing that setup and taking a look at the carburettor.

Hello

2009-11-03T03:17:00.001-08:00

Hey,

this is a brief page to keep up to date with all my pit bike + mini moto related projects and also customer repairs. so if you need something repaired or upgraded drop me an email at Glen.M.R@gmail.com anytime.

enjoy :)