If an engine is truely worn out, it will not run at all if it doesn't have sufficient compression. I have experienced this with both slug type and ringed engines. I had a ST.46 in a Chipmunk, that was running just great! Put in a flight, landed, waited my turn on the circle, and even with electric fingers it would not start. Gary Hajek was there and said the ring wore out, right on that last flight. I bought a ring from him, called Tom Lay and pleaded with him to tell me how to service the ST.46 so I could fly the Chipmunk at the SIG contest the following weekend, and he relented and told me. I gapped the ring, installed it, put in 5 or six ground runs to seat it and all was well after that!
Type at you later,
Dan McEntee