Stuck Exhaust Valves

[Colorguns]

What oil are you running? SO many thoughts on what oil to run! I was running Phillips x20-50 had 2 valves that were giving blow by on the valve stem, not stuck but blow by. TT 930 hrs Lyc 0-360

Are you running Aeroshell 100W Plus? as recommended by Lycoming?

Just wondering is all?

Doug

Doug

 

[Bowie]

I use Phillips XC20W50 and camguard I ran my last plane with lycoming O360 1600hrs with the same stuff and operated the same way never stuck a valve So who knows maybe the valve guides were set up too tight


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[okmike]

Back in the race car days we knurled the valve guides and they held oil in the knurls thus they always had plenty of lube, we would run 225+# of spring pressure which caused problems, knurling solved the problem.

 

[windy]

Camguard is supposed to help. Anyone seeing morning sickness with Camguard?

I ran Camguard with Phillips 20-50X/C for 1800 hrs in my engine until repeated stuck exhaust valves made me remove the cylinders to get them new valve guides & exhaust valves. I did the rope trick & reamed the guides to prolong operation before having to remove the cylinders.


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[Bowie]

Aerotech Engines out of Nova Scotia were at the Greenville Fly In, they told me that I'm operating properly, they also said they're getting low time lycomings with stuck exhaust valves coming to thier shop on a regular basis, as low as 80 hrs. Aerotech suggested to ream the guides slightly oversize, take out a little metal not just the coke, claim no sticking to TBO once done.


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[N86250]

Back in the race car days we knurled the valve guides and they held oil in the knurls thus they always had plenty of lube, we would run 225+# of spring pressure which caused problems, knurling solved the problem.

I have wondered why aircraft valve guides don't get knurled. I see knurling as an old technology to extend valve guide usefulness. I suppose it might affect the heat transfer from the valve stem to the guide to the cylinder head and overheat the exhaust valves.

 

[skywagon8a]

I have wondered why aircraft valve guides don't get knurled. I see knurling as an old technology to extend valve guide usefulness. I suppose it might affect the heat transfer from the valve stem to the guide to the cylinder head and overheat the exhaust valves.

Perhaps it is related to low rpm running engines? An aircraft engine red line of 2700 rpm is a fast idle for most other engines.

 

[julios]

What are you calling high compression over 8.7?

 

[Bowie]

What are you calling high compression over 8.7?

I didn't call it high compression, I'm calling it higher compression.Maules are available with a few variations of the 540. The J1A5D is rated 235hp at 2400rpm with a compression ratio of 8.5:1 The B model is rated 235hp at 2575rpm and the compression ratio is 7.2:1. The B model has an auto fuel STC available the J model doesn't, the J model weighs less than the B.


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[beezerboy]

knurled guides were out fast. last time I tried to get that done on a vintage motorcycle (about 30 years ago) the machine shop refused to do it. plus its not an approved procedure on aircraft engines

you only get combustion byproducts in the guide/stem if the valve leaks. how are the compression tests?

I think the put the guide to stem clearance too tight (as already mentioned). I have fixed a couple with the 'ol rope trick. they were stuck because the clearance got big (and out of round) & oil baked in the guide. read the SB.... they let you ream the hole out way big. and there is a wobble test discussed too.

plus 1 for checking the pushrods. they will bend. I would also check the dry tappet clearance

 

[Eddie Foy]

The Gospel According to Mike Busch.

"If the engine is operated with a rich mixture (particularly during taxi and other ground operations), lead, carbon, and other unburned combustion byproducts can build up on the portion of the exhaust valve stem that projects into the exhaust port when the exhaust valve is open. When the valve closes, this deposit build-up is dragged into the lower portion of the valve guide, and often causes accelerated guide wear (“bellmouthing”), particularly in Continental engines that use relatively soft valve guides. As we’ve seen, accelerated valve guide wear generally leads to valve hot spots (“burned valves”) and ultimately to valve failure (“swallowed valves”)."

Can someone explain how leaning prevents a stuck valve?

This problem has been solved years ago - run Marvel (or like-product) in the gas (and oil, if you want)...the old mechanics/aviators been using it for years to free/prevent sticky valves. I don't recall hearing them say to lean it more though.

 

[Eddie Foy]

The bulk of heat transfer in a exhaust valve occurs from the valve into the seat when it is closed.

I have wondered why aircraft valve guides don't get knurled. I see knurling as an old technology to extend valve guide usefulness. I suppose it might affect the heat transfer from the valve stem to the guide to the cylinder head and overheat the exhaust valves.