That's interesting... I didn't know they made 100cc engines with the two piece cylinder and head. Does it use the same head as the 80cc because I can't find any that are specifically for 100cc engines.
They all do but your better off with a single piece head , one gasket instead of two , however ports are different, unless you can machine, single is best.
I've had 4 of the Chinese craps, ran em till they failed, right after break in, BS if you like speed. The only one i screwed up was by misconstruing gas/oil mix ratio's in reverse, and i know I'm not the only one.
Ya, you can baby them a lil, but engines have a memory like cars...ya cant really baby it and then redneck it, if its gonna fail its gonna fail.
Im an ex builder of v8s,,, proofs in the pudding, if ya think its crap then ride them and have fun, give it at least a week, be sure shes oiled.
After i ran mine with wrong mixture, It froze up. I pulled the plug and threw straight 2 cyl oil in plug hole while it was still hot.
From my experiences, The single piece head motors are the best if they have a big intake. That was motor # 4...The cheap motors Aren't too bad. thats the one I fried, But a 66/80 would outrun a bigger 100... Uphill and especially downhill....All i'm saying is from my own experience.
Im going to finish a Yd100 right now....BTW, in rebuilding the Chinese motor, The the bottom end bearings are holding up OK, but the crank is a long stroke...LATER