rs670

My Feedback: (1)

I purchased this OS FS120 new and have not run more than a couple gallons of fuel through it. Originnally, the compression seemed fine. Lately, even though it starts and runs good, the compression seems really low. When turning it over by hand, I can barely tell when it comes up on compression stroke. The throttle is open and valve clearance is OK. Is it possible the ring needs replaced already and is this something I can do myself with standard hand tools?

Ken6PPC

I seriously doubt the ring is worn out that quickly. Try taking the glow plug out, dribbling some after run oil or automatic transmission fluid down the cylinder, and try it again. I bet your compression will come right back when it has some oil in the cylinder.

skorman

My Feedback: (3)

It sounds like the valves need to be adjusted. That can easily affect compression.

Nathan King

I concur. This sounds like it may be a valve problem.

bigedmustafa

My Feedback: (2)

Nathan should know, he works for Hobbico!

rs670

My Feedback: (1)

I appreciate the replies about valve adjustment maybe causing the problem but, in my original post, I stated that there is valve clearance. If there wasn't any, I could understand compression being affected. "Too much" clearance on the other hand would affect performance but not compression. If my thinking is wrong, please straighten me out. Thanks guys.....

Ken6PPC

No, you have it right. If you didn't have ANY clearance, the valves would never close completely. If you have too much clearance, you would still have compression.

rs670

My Feedback: (1)

Thanks for confirming my thoughts.... So, is there anything else to do other than replacing the ring?

Flyer95

My Feedback: (1)

What fuel have you been running in that engine? A castor/syntetic fuel is better for glow engines!

Ken6PPC

Nothing I can think of. Strange that it would be worn out within two gallons.

Ken6PPC

You might want to look at this ad:

http://www.rcuniverse.com/market/item.cfm?itemId=392991

I don't have any connection with this seller, but it seems to be priced right.

Here is Tower's price:

http://www3.towerhobbies.com/cgi-bin...?&I=LXCT32&P=Z

asmund

I had the exact same thing happen to a 30 fs that I just sold to a newcomer in our club. He suddenly had absolutely no compression even though I knew the engine was supposed to be like new, only just broken in. Problem was that I had told him to run his engine dry at the end of a flying session to avoid rust and somehow he had managed to run his engine so dry that it had absolutely no oil left in the sylinder. After I pulled the plug and squirted some fuel in it and cranked it up it was back to normal and running great.

togatoga

My Feedback: (42)

Sounds like your engine might have ingested something solid and has caused scuffing on the liner/ring.This might explain the lack of compression.The other thing might be damage to the valve/valve seat as the solid particle exited the engine. Sometimes the solid particle might be debris/flashing from the engine itself.
OS engines by virtue of design and manufacturing quality should exhibit strong compression even with little oil especially for a 120 size.I would disassemble the engine to have a closer look.