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Patrick1244

Member
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?
 
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.
 
sounds like a stuck valve

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.
 
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Experimental Chaos said:
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.
Click to expand...

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

http://www.lycoming.textron.com/support/publications/service-instructions/pdfs/SI1425a.pdf
 
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?
 
DanH said:
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?
Click to expand...

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? :confused:
Is it that an engine running with one "bad" cylinder can vibrate enough to crack a spinner bulkhead??? (Kinda "thinkin' out loud" here.)
 
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.
 
Patrick1244 said:
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.
Click to expand...

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.
 
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 ;)
 
Dan may be onto something here. At this point, with what you've described and done, you haven't even isolated it to a cylinder problem (exclusively). You may have a bad/loose prop. Sensenich or Hartzell? Inspect your spinner bulkhead and prop mounting carefully for hub cracks/leaks & security. Something made that cowl contact, whether prop/spinner movement or just a lot of jumping on the lord mount from a dead jug. Determine where that oil is coming from. If it is the front seal, try to determine if it has been leaking awhile or if it is new. If it is new, you should probably pull the soft cylinder and make sure you don't have a broken crankshaft at the same time. This could be as simple as a badly leaded plug or as bad as a prop or crank coming apart. Do a good compression check and check your filter & screens for chunks.
 
Oil

That was my question. I'm a long ways from being an engine guy, but I can't help but wonder, if it is a hung valve...........where is the oil coming from?
 
Also check your engine mount and the associated Lord mounts.

A compression test will quickly identify a bad cylinder and probably the general nature of the defect, if there is a cylinder defect.

Check the front crankshaft seal, too.

To me, the onset of vibration, the gouged cowl and the forward leak are all related and might - repeat, might - not be related to a cylinder issue.

When you've got the problem identified, please let us know what it was.

Thanks!

By the way, good job getting it on the ground.

Dave
 
Just a thought..........

Patrick1244 said:
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
Click to expand...


Clues here, possibly??

Constant speed prop, severe vibration, vibration varies with power, oil leak location.

I think you need to take a real good look at the prop----see if the blades are loose---fore/aft, up/down, or twisting pitch position.

Check the prob bolts too.

Just a case of "long distance diagnosis".

Low cylinder may be a "red herring"-----or I could be totally off base, that is quite possible too.
 
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Call me if you need help/ride/etc.

Hi Pat,
First - Great job getting down !!!
Al, called me and said you had trouble. I have no idea what the problem is, just lots of guesses. If you need a quick ride back to Ft Scott(?) give me a call - I still owe you a ride anyway. We're keeping our fingers crossed on the repair bill. Call me.

Steve
 
Patrick1244 said:
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
Click to expand...

Great job flying the airplane and finding a suitable place to land. For sure there was some pucker time until the tires met concrete.

The fact that the prop moved aft to hit the cowl indicates a major failure forward of the engine. (or the cowl moved forward to hit the spinner) The cylinders may well be ok. The crank shaft flange does fail sometimes and usually the prop leaves the airplane. I'd focus on the prop and the front of the engine above all else as a start. A visual inspection and dial check of the flange will tell its story quick.
 
If the engine is really running rough and shaking like it will when running on three cylinders instead of four, I think it is very easy for the engine to shake enough to cause the spinner bulkhead to be able to hit the cowling especially if the clearance between the two was relatively small to start with....
I would think that rough running and oil leak is likely one form of the following:
Bad cylinder
Bad prop
Bad cylinder installation
Bad prop installation
Of course the leak and the roughness might be two separate symptoms and not related to.....
Good Luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
Louise and I made a fuel stop in fort Scott this morning on the way back to Texas, and saw Patrick's airplane in the hangar with a couple of mechanics going over the engine compartment with a fine-toothed comb, looking for cracks and broken things I suspect. Of greatest interest to me were that two adjacent prop bolts were sheared off - the nut was completely missing from one, and the nut on the other was broken off the threaded portion, but jammed in the hub recess.

Not sure what that means, but it sure is interesting. I wonder if there is a problem in the hub that caused a blade mis-match or something. The rest of the plane sure looked nice - hope you solve this one easily!

Paul
 
I spoke with the A/P today. Yes there were two prop bolts that sheared and one that extended. The A/P is going to do a compression check and also pull the oil filter to see if he can find any metal. He did check the firewall and engine mount and did not find any stress cracks. I will keep you posted as I find out more info. Thanks to everyone for their insight.
 
I have seen this exact same thing happen on a F1 Rocket maintained by a A&P friend of mine. It appeared that the bolts were never torqued properly on a Hartzell which caused all but two of the studs to shear. Pretty amazing it didn't come apart.
 
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