Used OS 91 FX engine doesn't offer much resistance when I flip the prop
with my finger (the engine is not set to run, of course). There seems to be
very little compression. Is this common with this engine or does it appear
that I need to replace the piston ring - maybe the ring and also the piston?
I don't know the run hours on the engine. Any ideas? Many thanks,
Ollie 707-538-1855 Santa Rosa, CA.

I don't think I'd take it apart until after you've tried to get it running. It may run just fine.

Ringed engine or AB?, Is the piston oily? Thanks
OK, I looked it up, its a ringed engine, may only need some oil and little limbering up.

http://www3.towerhobbies.com/cgi-bin...I=OSMG0591&P=X

I'll give it a run, as suggested. As it stands, when I flip the prop it will turn half way
and create a clatter. Then on the following turn it will do a complete revolution
but only make a slight compression noise??? I'll run the engine in three or four days
and let you know the outcome. Thanks for the suggestions!