I have a 90cc Yamoto... Took it apart to replace the transmission shaft... and then during assembly... found out my timing chain shrunk... I never took the crank shaft or the parts on it out... did the top end... covers... split the case... replaced the shaft... put it all back together(i think) ... But when i was doing the top end... the chain seems like it should reach about a 1/4 inch or so more... i can't get the gear to go back on the cam shaft... Does anyone have any idea what may have happened?

It doesn't seem caught..... if i spun the crank the chain moves.... the tensioner is removed.... i am running out of thoughts...

 

Can you see the bottom sprocket? If not you probably have not got the chain on it properly, either off completely and running between crankshaft sprocket and case, or with a link at the bottom looped out. If it is this, carefully turning the crank through 180 degrees whilst keeping the chain fairly tight, will get he chain on the lower sprocket properly.