My buddy got a replacement cylinder for 49cc China girl engine but the original piston and rings is too small but it came with a piston and rings that's fit it. It's not 40mm, and it's not 47mm (66/80cc). we measured it at 42.7mm. I think I can get a pic, but it looks just like every China bike engine and fits over engine studs fine also stock head fits it but new bottom gaskets are a hair too small. What now is the engine size in cc? Is this ever heard of?