rcStan:

When you get your new parts be careful. Some of the ST pinned rings did not have the pin in the ring gap, but rather there was a small notch near the end of the ring the pin went in.

If yours is this version putting the ring in wrong way around will also lead to premature failure, if the engine will even turn. This may be why yours stuck at assembly.

Looking at the top of the piston the gap should be positioned in a counterclockwise direction from the pin.

Hope this helps.

Bill.