My "jammed" but not seized new 48cc 2stroke bicycle engine

[GingerInAdelaide]

Hello, in the belief that everything is always fixable, I thought I'd ask people with a bit more motor knowledge and tech savvy .....
Within the first kilometre of running-in a newly installed 48cc two-stroke mo-ped motor, going up a slight incline and pedalling all the while, I thought I'd seized it from wrong mix. But, now I've had the head off, I can see that the piston runs freely - no damage - and it can be manually cranked through many cycles, many full revolutions of the gear wheel. But then eventually the mechanism jams again. Being single cylinder, the rod sits in-between two sides of a split crank, like a double wheel. There doesn't seem to be a problem with wrist-pin bearings, crank bearings or either axle bearing (all of which are needle-in-cage design). The left-side crank cover is clearly scored by some foreign object seemingly trapped between the crank-case and the crank. Would this account for why the engine parts all move freely then get stuck again? And if so would it be possible to just remove the head, upend the bike and shake the debris out. OR is it likely to have done serious damage requiring a new bottom assembly to be bought/installed?

 

[brendonv]

its not really going to hurt it tipping it upside down and shaking it. Shake it n see what comes out. A bit of the crank or something may have come off so by shaking it u can see what has broken off and then no what to replace. If the crank case is scored then it will still run, its only if the cylinder or piston is scored then u gotta replace it. Having a scored crankcase in theory shouldnt affect performance.

Hope that helps,
From Brendon.v