O360A1A Valve/Cylinder Failure?

[Patrick1244]

Today I was flying my RV6A. I have a lycoming O360A1A with about 1060 hours on it. I also have a constant speed prop. About an hour into the flight I experienced significant engine vibration. I powered back and landed about 5 minutes later. I did power up for a few seconds while heading to the airport and again experienced significant vibration. I think the oil pressure was OK but honestly my focus was getting to the nearest airport.

Once on the ground I noticed that my spinner had made contact with the front of the cowling and put a gouge 1/2 inch wide and probably 1/4 inch deep. I also noticed a small amount of oil on the nosewheel. I pulled off the cowling and found a small amount of oil right behind the alternator belt. There was no other oil around the cylinders, back of the engine or firewall

I pulled the prop through and noticed that there seemed to be low compression on one of the compression strokes. Here are some of the questions I have?
Does this sound like a failed valve or cylinder?
What is the best way to confirm it is a failed valve or cylinder?
Any idea the cost of repair?
If one cylinder failed would you expect problems with the others?
Would you recommend a top overhaul verses just replacing a cylinder?
How much is a top overhaul
Any other ideas suggestions would be appreciated
If not a failed cylinder what else could it be and how would you check it?

[Russ McCutcheon]

With that number of hours it is very possibly a stuck exhaust valve, remove the rocker cover and check for the exhaust valve not closing, if this is the case you may have gotten off cheap and just need to ream the exhaust valve guides. It also sounds like you need experienced hands on help, get some, you will learn a lot.

[Experimental Chaos]

I have to agree with Russ. In my experience (A&P for 35+ years) a well cared for, regularly flown Lycoming normally makes TBO or better, (Continental, is a different story) but they can have a stuck valve at about the half-way point. It’s worth a check, but this absolutely warrants a comprehensive check out by someone that knows what they are doing doing. If you find a stuck valve, you’ll get by for a reasonable price.
I would also, check the oil screen and filter, to confirm that it’s not making metal.
There’s an article in a recent EAA magazine that shows how to do what we always called the “Indian rope trick” for freeing stuck valves. I also agree with Russ, that you should get someone who has done this before and help him, I don’t think I would recommend this for someone not completely comfortable working on an engine.
Oh, if you do find a stuck valve, be sure to check the pushrods for straight.
You may hear some recommendations for Marvel Mystery Oil, and while I’m not against it, I’m not sure I’m for it either.

[az_gila]

Originally Posted by Experimental Chaos

I have to agree with Russ. In my experience (A&P for 35+ years) a well cared for, regularly flown Lycoming normally makes TBO or better, (Continental, is a different story) but they can have a stuck valve at about the half-way point. It?s worth a check, but this absolutely warrants a comprehensive check out by someone that knows what they are doing doing. If you find a stuck valve, you?ll get by for a reasonable price.
I would also, check the oil screen and filter, to confirm that it?s not making metal.
There?s an article in a recent EAA magazine that shows how to do what we always called the ?Indian rope trick? for freeing stuck valves. I also agree with Russ, that you should get someone who has done this before and help him, I don?t think I would recommend this for someone not completely comfortable working on an engine.
Oh, if you do find a stuck valve, be sure to check the pushrods for straight.
You may here some recommendations for Marvel Mystery Oil, and while I?m not against it, I?m not sure I?m for it either.

The "Indian Rope Trick" is officially described here...

http://www.lycoming.textron.com/supp...fs/SI1425a.pdf

[DanH]

When you pulled it through, a cylinder had low compression or zero compression? Maybe you may have an unhealthy valve, but.....when you had the cowl off did you examine the spinner bulkheads?

[PCHunt]

Originally Posted by DanH

When you pulled it through, a cylinder had low compression or zero compression? Maybe you may have an unhealthy valve, but.....when you had the cowl off did you examine the spinner bulkheads?

Dan, I always learn something from your great posts, but this one has got me stumped! I'm trying to figure out what spinner bulkheads might have to do with low compression? Or........ maybe it's the other way around?
Is it that an engine running with one "bad" cylinder can vibrate enough to crack a spinner bulkhead??? (Kinda "thinkin' out loud" here.)

[Ron Lee]

Thanks Pete. Normally I am not ashamed to admit I don't know much about a lot of things. This time I am so far out that I wasn't sure where I was uninformed. But Dan must have a point worth noting.

[Mike S]

Originally Posted by Patrick1244

Once on the ground I noticed that my spinner had made contact with the front of the cowling and put a gouge 1/2 inch wide and probably 1/4 inch deep.

Methinks Dan was referring to the above.

The contact between the bulkhead and cowling may have been caused by a failure of the spinner bulkhead, or may have caused damage to the bulkhead, not to mention what the vibration mentioned can do to it.

[PCHunt]

Duuhhh!
Shoulda re-read all the postings.............

[DanH]

Right....a weak cylinder shouldn't in itself cause the spinner to cut deep into the cowl. However, it might fatigue a spinner backplate, or maybe the backplate is broken and is the true cause of the vibration, or maybe he has a weak cylinder and a bad backplate....or maybe this is all horsespit, another case of long distance diagnosis gone wrong