I just baught a os rg .21 motor, and when i recieved it today it was really tight with good compression. The problem is that it seams to have a clank when the piston hits the top of its cycle. Is this normal for a new engine? there is no oil or gas that hs been in it yet, so could it be there is just friction right now or do i have a junk motor?

Thats normal. They are tight when new which is a good thing.

so your saying when it hits top it should clank. i have a sirio .27 that is brand new and very tight, but doesnt clank.

If you mean the play you feel when piston is at TDC then that's normal. If you open up the back plate and look at the rod and crank when the piston is at TDC you can turn the crank slightly without the piston movin.

Completely normal. It feels slightly different on different engines.