Correcting squish on one piece headkits

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.