Exhaust valve problem options

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blsewardjr
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Exhaust valve problem options

Post by blsewardjr » Sat Feb 09, 2019 8:06 pm

During my annual this week my mechanic discovered that my #1 cylinder had a compression of 45/80 warm. Upon borescoping it he found that the exhaust valve was showing early signs of wear. Faced with pulling the cylinder to the tune of several AMUs, he offered the option of "lapping" it. The operation was successful, getting the compression up to 63/80 cold. We're going to look at it again in 25 hours. My mechanic runs a podcast on aircraft maintenance and I was the subject this week. If you're interested it's at http://airplaneownermaintenance.com/109 ... od-option/ Bernie
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Re: Exhaust valve problem options

Post by waynemcc999 » Sat Feb 09, 2019 9:00 pm

At my last annual, I had a burnt exhaust valve... decided to replace with a new full cylinder kit at cost of $1200 parts and a few hundred dollars labor. At the time the aircraft had 1800 tach hours and that was the first valve problem and therefore first cylinder replacement.
Last edited by waynemcc999 on Sat Feb 09, 2019 10:40 pm, edited 1 time in total.
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Re: Exhaust valve problem options

Post by Hans » Sat Feb 09, 2019 10:23 pm

How many hours on engine ?
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Re: Exhaust valve problem options

Post by blsewardjr » Sun Feb 10, 2019 2:02 am

650
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Re: Exhaust valve problem options

Post by Pilot55 » Mon Feb 11, 2019 1:56 am

Usually the valve seat problem starts with valve guide wear. The valve now does not stay concentric with the seat and when the valve is seated does not make enough contact with the seat to pull the heat out of the valve. It also puts higher point loading on a smaller area of the seat and causes the seat and the valve to pound out in that area. The lapping will help for a period of time but if the seat is worn it will return.
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blsewardjr
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Re: Exhaust valve problem options

Post by blsewardjr » Mon Feb 11, 2019 2:08 am

Bret- That what my research revealed as well so I had my mechanic check the guides. He says he didn't find any slop in them. That said, I agree that the problem will probably eventually return. Nonetheless I'm trying to follow Savvy's Mike Busch's advice to do whatever you can before pulling the cylinder. Busch believes that pulling cylinders can, if you're not extremely careful, result in much more serious engine problems. See
https://www.savvyaviation.com/wp-conten ... afraid.pdf Bernie
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Re: Exhaust valve problem options

Post by ZAV » Mon Feb 11, 2019 2:53 am

That was a scary article.
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blsewardjr
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Re: Exhaust valve problem options

Post by blsewardjr » Mon Aug 05, 2019 5:38 pm

We did the re-check and as Bret predicted the valve guide is now very wobbly and low compression has returned. We’re going to pull the cylinder. Any experience with re-build vs Lycoming vs Superior vs ECI? Thanks. Bernie
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Re: Exhaust valve problem options

Post by Steve » Tue Aug 06, 2019 6:37 pm

Sorry, can't give any advice about what kind of cylinders...

Lycoming recommends checking the valve guides every 400 hours on our engines. I've only done it once (at around 500 hours, and it was OK). There is a Lycoming SB to do the test:
It requires the use of a ridiculously expensive tool. I, being an inveterate eBay surfer, was able to get one for much less than the list price several years ago:
IMG_3074.jpg
If anyone needs to do this SB, and their mechanic doesn't have the tool, I would be willing to loan it out...

Steve
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