hello to all

I order from USA one TT pro46 engine. In package is engine, muffler, instruction, decals and set of two wrench. In little bag with wrenches is one small, abt 3mm diam. gummy o-ring. This ring is big question for me. Where I can put this o-ring or this is for spare, but for what ?

And second question is when I put engine in tdc i hear "klak". In this position I move Crankshaft cca 1mm fore and aft, but piston is stay in tdc. Is this normal ?

Thanks again

Realdo