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OS 300 Twin

Old 04-30-2007, 07:15 PM
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Default OS 300 Twin

Question for Bax.

I have been operating an OS 300 Gemini for the last two years. This weekend I flew it in my Christen Eagle for the first time this year. I experienced an overheating problem on the left cyl. Engine quit in flight. After examination, the left cylinder was lacking compression. I disasembled the cylinder head and found a Gaulded Piston. I am sending the engine back to OS for repairs but what really concerns me is why the left cylinder overheated. The right side appeared normal. I know I did not overlean this engine but I suspect that I had a stuck piston ring from sitting up all winter.
Any chance I'm right? Or please offer your opinion. I don't mind the repairs as this has been an excellent powerplant and the second best engine I have. It is second only to the OS sirrius radial :^).
Thanks for your help
Glenn Sheppard
Old 05-01-2007, 01:52 PM
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Default RE: OS 300 Twin

One cylinder in any multi-cylinder engine will tend to run leaner than the others. One will always be the richest. It's likely your engine was a bit over-lean on one cylinder.
Old 06-08-2007, 05:46 PM
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Default RE: OS 300 Twin

I returned the engine in question to Hobby Services and had it rebuilt. New cylinders, new rings, one new piston and a front bearing. All repairs appear in good order. However as I began to break it in again, I noticed the left cylinder was getting hot. I set the engine to around 4000 rpm and measured the cyl. temp. Right cyl was 135 degrees, left cylinder was 176 degrees. I then shut the engine off and checked for intake manifold obstructions but none were found. the valve clearance appeared adequate and was equal both sides. "O" rings on manifold appear good with no cracks or pits and a tight fit on both sides. I figure they were replaced at rebuild.
Now the question, What to check for next? BTW, this engine is three years old and has had no more than two gallons of fuel .
Thanks for your support

Glenn Sheppard

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