Bought a Moto 4 ( 100cc) for the kid that was smoking. Got some rings, honed the cylinder, put it back together, ran good, but timing chain was a little loose, I didnt have the tensioner installed properly. Took head back apart, re-did the timing chain tensioners, looked much better. Started it up, run good, but I forgot to tighten the bolt that holds the timing sprocket on. It came loose, motor dies of course, but when I put the sprocket back on, it doesnt run at all now no matter what. I check to make sure its up on compression and align the mark on the flywheel with the mark on the timing housing , still nothing. Took it apart again, everything looks fine, piston still good, valves actuate fine. What the heck did I do? Did I destroy the head somehow? Motor seems to be low on compression now.