GR mini's project page: One piece into two piece cylinder head conversion

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: