I have used this engine for over one year and it has been super reliable, one of 4 OS's I have. Yesterday it would not start. Glow plug ok, fuel lines ok, removed head to see if cracked or dirty, but the engine when finger flipped will only softly pop once and not run out the prime or other fuel. It also feels as if compression is down somewhat, especially compared to the other OS engines. I am at a loss as to what to do. Help

I removed the muffler and when looking at the side of the piston in the exhause port I see two small groves in the piston, maybe from dirt or debris, but perhaps metal from something. When turning the prop it is clear that air is escaping past the cylinder and bubbles of oil or fuel are seen in the port. I imagine that the piston and sleeve are scored enough to leak on compression. Will replacing the two items correct the problem? Placing heavy oil on the piston will temporarily increase felt compression which tends to confirm the cause.

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how many hrs / gallons of fuel have you ran thru it?? what is the use of the motor? like crazy 3d hangin on the prop??? stuff like that.. very possible a bit of dirt got in there or it was run lean a few times.. if the top of the piston is black then it was lean (not doubting your ablities) but if the piston is scored so much that you can feel it when you lightly drag your fingernail over them then i would replace it.. also do you run after-run oil in it? check bearings may have one going / gone bad.. hope this helps

also do a search on the cylinder peeling episode.. the older ones had a problem with the chrome i think it was peeling how old is the motor? need more info
p.p.s- get an electric starter if you dont have one it will save you headaches!!

The engine is about 8 years old but has only been run for the last 2 years, about one or two gallons of fuel, mainly sport flying. I have hit the ground several times, flying in a large pasture while our flying field is being rebuilt as part of a new ampitheatrel. The piston is clean and not visibly discolored, and I am careful to not run my engines too lean. One scratch is visible clearly and can be felt with a fingernail. the bubbles seen on compression tell me that loss of compression is serious. Gentle pressure maintained on the prop will all the prop to gradually turn as pressure is lost. I have 3 other OS engines and all have more compression than this one. Odd thing is that it just quit after 4 excellent flights the day before.

the leak around the ports is semi normal but if its excessive i would check to make sure the bolts are tight on the head and on the back plate... check to make sure the carb is on securly.. other than that i would maybe order a new piston and sleeve

Crashes can easily result in dirt ingestion. That would be a sure source of scoring.

An eight-year-old .46 FX is not likely to have the peeling difficulty because it would be one of the early ones. Peeling was a big difficulty about four years ago, when OS changed methods due to the Japanese EPA-type ministry.

thanks bax i was under the impression it was the old ones.. didnt mean to post mis information