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kerrjohna(at)comcast.net
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 Posted: Wed Sep 07, 2011 9:15 am Post subject: sticking valves |
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Reading all of the comments regarding stuck engine prompted me to report on the sticking valves. Could not find anything in the mainenance manual for the 912, but have not attended the class either. It is on my bucket list.
Relying on the suggestions from Lowell and others a systematic approach based on others past experience Marvel Miracle Oil was added to the oil following an oil change. The condition of a single valve sticking on startup additional valves began sticking. The problem became progressively worse until the point of the propeller spinning like a turbine. Obviously the problem was acute rather than chronic.
The initial assumption by many was that it was the exhaust valves sticking due to carbon or some other build up.
After removing the rocker arm covers and pulling the propeller through it was determined that it was the intake valves that were not returning to seat. Because of the sudden appearance of the problem and its quick escalation it is likely that bad fuel was introduced at the last gas up (Phillip 66, medium grade, no ethanol).
My go to A&P, test pilot, and guru of all things aviation related suggested a slug of Techron in the gas up to double the recommended mix. But to solve the immediate problem of no compression the valve stems were slathered with carburetor cleaner and then the valves were "staked" (repeated impacts allowing the valves to reseat). Compression, weak, was obtained in two or three of the cylinders then the engine started. The balky cylinders soon came on line and the engine was run for 30 minutes at medium rpm. The engine was then allowed to cool and 10 gallons of Supreme Chevron with techron was added to the tanks. The engine fired right up and the plane was flown for an additional 1/2 hour.
After sitting for 2 days the engine had good compression and started immediately, running on all 4. A 30 minute flight showed excellent performance and indicates that the problem is solved.
There are bound to be second guesser out there who would have suggested a different approach but each step was thoughtfully approached with knowledgeable advise based on the currently available information with each step leading closer to the solution.
John Kerr
Classic IV, 912ul, 800+ hours
[quote][b]
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lcfitt(at)sbcglobal.net
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| Posted: Wed Sep 07, 2011 1:40 pm Post subject: sticking valves |
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John,
I guess I have to be a bit more careful when I post. The ATF we used instead of the unavailable Marvel Mystery oil was put into the fuel tanks - a quart each wing. The guess at least, was correct as our treatment focused on the intake valves. Your thorough diagnostics is very helpful.
Thanks,
Lowell
From: kerrjohna(at)comcast.net (kerrjohna(at)comcast.net)
Sent: Wednesday, September 07, 2011 10:11 AM
To: Kitfox (kitfox-list(at)matronics.com)
Subject: sticking valves
Reading all of the comments regarding stuck engine prompted me to report on the sticking valves. Could not find anything in the mainenance manual for the 912, but have not attended the class either. It is on my bucket list.
Relying on the suggestions from Lowell and others a systematic approach based on others past experience Marvel Miracle Oil was added to the oil following an oil change. The condition of a single valve sticking on startup additional valves began sticking. The problem became progressively worse until the point of the propeller spinning like a turbine. Obviously the problem was acute rather than chronic.
The initial assumption by many was that it was the exhaust valves sticking due to carbon or some other build up.
After removing the rocker arm covers and pulling the propeller through it was determined that it was the intake valves that were not returning to seat. Because of the sudden appearance of the problem and its quick escalation it is likely that bad fuel was introduced at the last gas up (Phillip 66, medium grade, no ethanol).
My go to A&P, test pilot, and guru of all things aviation related suggested a slug of Techron in the gas up to double the recommended mix. But to solve the immediate problem of no compression the valve stems were slathered with carburetor cleaner and then the valves were "staked" (repeated impacts allowing the valves to reseat). Compression, weak, was obtained in two or three of the cylinders then the engine started. The balky cylinders soon came on line and the engine was run for 30 minutes at medium rpm. The engine was then allowed to cool and 10 gallons of Supreme Chevron with techron was added to the tanks. The engine fired right up and the plane was flown for an additional 1/2 hour.
After sitting for 2 days the engine had good compression and started immediately, running on all 4. A 30 minute flight showed excellent performance and indicates that the problem is solved.
There are bound to be second guesser out there who would have suggested a different approach but each step was thoughtfully approached with knowledgeable advise based on the currently available information with each step leading closer to the solution.
John Kerr
Classic IV, 912ul, 800+ hours
[quote]
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