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Interesting find today

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Jrskygod

Well Known Member
I'm doing my condition inspection and the intake valve on #4 cylinder apparently has an issue. Compression on that cylinder went from 78# to 74# in the last 18 hours and when borescoped it has a definite hot spot. I really don't want to pull the cylinder unless necessary so what should be my plan of action?

Stake the valve and fly it for 10 hours or so while monitoring it and hope for the best or just go ahead and try lapping it in place in hopes of resolving the issue. Any other suggestions?


intake valve.jpg
 
Jrskygod said:
I'm doing my condition inspection and the intake valve on #4 cylinder apparently has an issue. Compression on that cylinder went from 78# to 74# in the last 18 hours and when borescoped it has a definite hot spot. I really don't want to pull the cylinder unless necessary so what should be my plan of action?

Stake the valve and fly it for 10 hours or so while monitoring it and hope for the best or just go ahead and try lapping it in place in hopes of resolving the issue. Any other suggestions?


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I was told by Savvy that the valve rotator cap could cause this. Replacing it might be easier than lapping.
 
The picture looks like the valve is not centered on the seat. Look at it again and make sure its not an optical thing.
 
664781 said:
The picture looks like the valve is not centered on the seat. Look at it again and make sure its not an optical thing.
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I see what youy’re seeing, but I think the valve is open, and that is causing the illusion.

I don’t think staking it is going to do much for you, but if you take of the valve cover and rockers to do anything else, it doesn’t cause harm. I agree with Carl that you should make sure its rotating - if you take of the rocker and sprint, sprint he valve a bit and visually inspect the rotator - pout it back together and fly it a bit, then check again. Lapping isn’t all that hard, and its better to do it sooner rather than later as the more you let the seat erode, the less likely it is that it will solve the problem….
 
I agree with Paul. Staking works if you have low compression due to a piece of carbon under the seat, or sometimes a stuck valve if you get lucky, but any real issue seems to always come back.
If you can, open the valve fully and inspect the seat under the hot spot if you can. If it’s a crack, lapping won’t fix it. If it’s the rotator, lapping will only temporarily fix it and you will be back to square one.
 
I assume you are talking about the burned area? If so, it is a bit unusual but certainly possible it is burned on intake. If there is a rotator (all engine intakes don't have them) then definitely replace that, also check valve lash with the lifter collapsed to be sure it has not reached the lower limit due to recession (i think not) or cam/follower wear. (more likely) Definitely get a view of the open valve do validate this assumption. If confirmed, then (I would) lap in situ. It is not going to get better. It is leaking. Staking/whacking is unlikely to make an improvement if confirmed as a hot area.

Do let us know what you find. Definitely don't add to the problem with additional flight time. Not really unsafe, except to the wallet.

Is this a high output 340 per chance?
 

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I may be out of line here but I have seen compression readings vary by that much or more on the same cylinder after a couple flights. Is 78 to 74 a justification to lap a valve or pull the rocker arm off? What harm would come from another flight or two and recheck. The likelihood of a burned intake valve is much less than an exhaust valve.

A subscription to Savvy may be money well spent.
 
Not my intake, but I recently lapped #3 exhaust. Pretty simple process. First pic hot spot, second 10 hours later. I replaced rotator just because. Lycoming don’t have the no rotation issue like continentals have. I thought the process was simple. First time Ive worked on the innerds of an engine.

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climberrn said:
I may be out of line here but I have seen compression readings vary by that much or more on the same cylinder after a couple flights. Is 78 to 74 a justification to lap a valve or pull the rocker arm off? What harm would come from another flight or two and recheck. The likelihood of a burned intake valve is much less than an exhaust valve.

A subscription to Savvy may be money well spent.
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I agree with the idea that if all I had was a small drop in compression, I’d just fly it. But now that we all use borescopes and can see things we couldn’t before, if I see a symptom developing, I’d address it before it gets worse. In this particular case, in The past, I’d have just run it - but we are smarter now.
 
BH1166 said:
Not my intake, but I recently lapped #3 exhaust. Pretty simple process. First pic hot spot, second 10 hours later. I replaced rotator just because. Lycoming don’t have the no rotation issue like continentals have. I thought the process was simple. First time Ive worked on the innerds of an engine.

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Good job! It can be intimidating to work on your own engine, driven by the seriousness of the consequences of doing it wrong, but in reality, they are quite simple. There is also a tremendous pool of resources to get help and advice .
What separates the pros from us hobbiest is they are much more efficient at it !
 
Not specifically answering OP question but though some may find this interesting. Attached are pictures of my valves over time on a 390. Not only are they different from cylinder to cylinder but also over time. I find it interesting that two valves developed a yellow ring on them for a short time. Any thoughts? Only run LOP.

Screen Shot 2024-06-06 at 5.21.11 AM.png
 
I took off the valve cover today and there is no rotator on the intake valve of this engine. O-320-D1A. I didn't have time to do any other investigation. Next time out Ill open valve and borescope again.
 
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