G

gmshelley

Member
Yesterday N818GS made it's first flight after 5 years of building. Everything went beautifully untill about 20 minutes into the flight when the engine had a reduction in power :eek: I made a precautionary landing and we had found the #2 cylinder plugs fouled and the belly of the plane covered in oil. There was also oil dripping from the carb. We did a compression check and the #2 was reporting 76 psi. We also checked the cylinder oil return and breather with no problems noted. We cleaned everything up and test ran with no issues. Made the second flight and 15 minutes in we lost #2 again. We lost almost a quart of oil and the EGT and CHT were never as hot as the other three cylenders.
I'm asking for the engine experts to chime in and give me some ideas.

Thanks in advance.
 
Not an engine expert, but could you tell what engine you're running? Sorry to hear of your troubles.
 
Thanks for the prompt replies.
The engine is a O-360 with 0 smoh and 1600 tt.
I had bought the engine after it was overhauled from a builder in NY.
The shop that completed the OH was a reputable builder in the area.
 
Well firstly, you are a lucky guy.

Secondly, I wouldn't leave the ground again until I had diagnosed and fixed the problem.

I would offer valve guides and seals as being the problem. You can still have compression with the valve seats being OK and the guides wallowed out.

Oil in the carb ---- it probably just ran down the induction tubes when the engine was stopped and sitting there awaiting further attention.
 
I just talked to my guy at the local FSDO. He stated that the rings are not seated in that cylender. He said it's not uncommon. I'm right now running my engine at 2500rpm or better than 75% power. He said to not be concerned until you get to 10hrs. If things haven't gotten better than you might have an issue with the rings not wanting to seat. To get the rings to seat you need to push it. like I said, 2500rpm or better than 75% power. I would put oil in go up over the field, monitor the oil usage and run er hard. just to be safe, I would contact your engine manufacture.
 
Is it possible you've got water in the oil? Once the oil reaches operating temp (fits with your flight times before problems) that water will start boiling and could "froth" the oil enough to start dumping large quantities out the breather into the carb, explaining the loss in power and the oil on the belly as well as oil in the carb. In that case, however, I would expect to see fouled plugs on all the cylinders, not just #2. Did you check all the plugs? What about compression on the other cylinders?

On your intake manifold, if you had lots of liquid oil running into the manifold, would the physical layout of the manifold encourage puddling of oil and more delivery to #2 than the other cylinders?
 
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I'd definitely get a second opinion before I flew again. That diagnosis doesn't sound plausible to me.

Perhaps Mahlon (Mattituck) can chime in.
 
allbee said:
I just talked to my guy at the local FSDO. He stated that the rings are not seated in that cylender. He said it's not uncommon. I'm right now running my engine at 2500rpm or better than 75% power. He said to not be concerned until you get to 10hrs. If things haven't gotten better than you might have an issue with the rings not wanting to seat. To get the rings to seat you need to push it. like I said, 2500rpm or better than 75% power. I would put oil in go up over the field, monitor the oil usage and run er hard. just to be safe, I would contact your engine manufacture.
Click to expand...

I agree.

The write up would lead one to conclude oil is entering the combustion chamber and its route most likely is via improperly seated or improperly installed rings.

Clearly, a major problem is indicated by loosing that much power and oil in such a short flight. To be most safe, #2 cylinder could be pulled and checked for proper ring installation and side wall glazing. If there is glazing, a hone job of the side wall in is order.

If there is a written record of the overhaul, check to see exactly what was done. "Major Overhaul" is a meaningless term without qualification. Does the engine have new cylinders or are they original, simply cleaned up and in service limits? Same with the valves. If the cylinders are new, it probably is a ring seating break in issue. If they are original, something else is totally not right.
 
# 2 not seated yet

gmshelley said:
we lost #2 again. We lost almost a quart of oil and the EGT and CHT were never as hot as the other three cylenders.
Click to expand...
Seen this before- my vote is #2 is not seating and may need a re-hone and check rings and cyl walls. You would hear the blow-by in the exshaust or carb if a valve was not seated correctly and diff. pressure would be lower than 76/80. yea, I would pull #2...
 
Just as a question, what kind of oil are you using for break-in?

If you are taking a Poll:
intake valve guide seal
Rings not seated yet, or improperly installed.
 
another possibility...

...is a cracked sump? If you pulled a couple of the inlet pipes, you might see a clue as to whether oil is coming from this direction.
 
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OK, way too many possibilies to list here. Could be unrelated problems but, I'd start at the mag, pull the plugs on the mag and check to see if there is any oil inside of them. A shaft seal gone would allow oil into the mag, effectively putting out the spark, and if there is enough, leak out and down the engine.

Also more details on the engine and setup? O-3x0-X#X?, CS or FP? Pictures of the leaks. If you don't find it quick, find a good mechanic too look over the engine. In my experience, FSDO guys know even less than a typical jet mechanic about pistons. Don't listen to anyone who told you this is NORMAL.

Edit: also I'd rule out valves and ring seating right away because of your compression. Is the oil running down the INSIDE of the carb or the OUTSIDE?
 
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Thanks for the inputs.
The engine is a 0-360 A1D that was coverted to fix pitch and using impulse mags. I'm using Aeroshell stright mineral oil.
Also 98% of the oil loss is through the #2 exhaust pipe.

Thanks.
 
I still say that the fella that I was talking to, really knows his RV's and the lics. I stated your problem with 1 quart of oil and he said, not uncommon. I would call your engine rebuilder and asked what he thinks before you do anything else.
 
I'm sorry, but using enough oil to lose power on one cylinder is certainly NOT normal. It sounds to me like there is definitely a problem with that cylinder. Look at the cylinder walls with a bore scope, check the valve guides and if you can't find the problem, pull the cylinder.
I would also notify the engine builder and let them know what's going on.
I've overhauled a few Lycomings in my day and have never seen this kind of result as "normal".
 
I'm trying to picture how non-seated rings would allow a stopped engine to pass oil out the carb. unless perhaps they were missing and the engine was way over filled. On the other hand, I can easily see how fried guides could do it. Also, there seems to be some confusion in this thread about guide wear versus valve seat wear.

In any case, I can't imagine taking it back up until I had a solid explanation. Losing power over the field at 1000' is no big thing, losing it at 200' AGL during climbout would be a bad thing.
 
szicree said:
I'm trying to picture how non-seated rings would allow a stopped engine to pass oil out the carb.
Click to expand...
Steve, I think the theory here is that if there is excess oil pooling in the cylinder and the engine is shut down with the intake valve open, oil could run down the intake tube and out the carb.
 
I had a friend with a fresh overhaul (form a good shop) have horrible problems with low compression - turns out the shop used the wrong rings with his freshly-chromed cylinders. Even good shops can make mistakes sometimes - maybe you got the wrong rings for that jug?

Just brainstorming "out of the box"
 
OR

maybe the tech guy broke the oil ring when he installed it.

OR

I still keep getting back to the valve guide. Since its a newly overhauled engine, it wouldn't be wear. So it could be a broken stem seal. I am not even sure a bad or gone seal could provide this much oil to the combustion chamber.

Either way there is nothing normal about the situation. You're "blowing oil" not merely consuming a little.

JMHO
 
Not "normal"

Mel said:
I'm sorry, but using enough oil to lose power on one cylinder is certainly NOT normal. It sounds to me like there is definitely a problem with that cylinder. Look at the cylinder walls with a bore scope, check the valve guides and if you can't find the problem, pull the cylinder.
I would also notify the engine builder and let them know what's going on.
I've overhauled a few Lycomings in my day and have never seen this kind of result as "normal".
Click to expand...

There is something weird going on in that cylinder. As Mel has said, borescope it, look at the guides, and pull the cylinder if there isn't a clear cause. Remember that this is a "zero time" engine, not an in service engine that developed a problem, so anything is possible. From this distance :rolleyes: I would vote for a valve guide issue, not wear obviously, perhaps moving in the head.

John Clark
RV8 N18U "Sunshine"
KSBA
 
John Clark said:
Remember that this is a "zero time" engine, not an in service engine that developed a problem, so anything is possible.

John Clark
RV8 N18U "Sunshine"
KSBA
Click to expand...

This is the most relevant statement I've yet seen on this thread.

Also, I understand that oil could flow through an open intake valve, but I'm picturing an arrangement similar to the photo here

http://www.sacskyranch.com/combustionClean.htm

It seems like the oil pool would have to be awful deep to pass out through the valve.
 
valve guides

My vote would be valve guides and seals.
Second vote would be either a broken oil-control ring, or wrong ring.

No way 20 minutes of running is going to do anything like glaze cylinder walls. Of course none of the rings are really seated yet, but the amount of oil blowing through that you are talking about is not from unseated rings.

There seems some confusion about valve guides and seals having anything to do with compression - they dont. The valve can still close and seat well for the compression test, but when running, oil is traveling along the valve stems and mostly going out the exhaust. Some is getting into the intake.

It sounds kinda like if it is a reconditioned cylinder, they forgot to replace the valve guides.
 
Call the shop that overhauled the engine and explain the issue.

Then Call Mahlon Russell.

Pull the jug and piston.

Have it checked/overhauled by a reputable shop.

Install the overhauled jug/piston.

Have fun.

Good luck and blue skies.
 
I'd be pulling that cylinder and borescope the other three at this point. There is deff major problems.
 
Mel... it appears we...

Mel said:
Steve, I think the theory here is that if there is excess oil pooling in the cylinder and the engine is shut down with the intake valve open, oil could run down the intake tube and out the carb.
Click to expand...

...are talking about the exhaust pipe, not intake tubes...

See post # 14

Can lifters go bad at some rpms and not others? ...or hot vs. cold?
 
Gary,
This is my first time posting on this forum so I hope it works.
I had the exact same thing happen to me when I got my new overhauled engine for my RV4. This was some 18 years ago and was not done by a reputable shop as yours was. Fortunatly I had a freind who had a flying RV4 thats engine was in the shop for overhaul and we decided to break it in on his airplane rather than test fly my airplane and engine at the same time. End result was the same problem. We pulled the jugs and found 2 cylinders with broken oil control rings. After closer inspection we found they were the wrong rings. To make A long story short I didnt feel I could trust the rest of the engine so I tore the whole thing down and overhauled my first lycoming. A boroscope is a good Idea but chances are good that you wont see anything. The oil running out of the carb is a good indication of a ring problem. I doubt its a break in issue but its possible. I would try and find a possitive solution prior to flying again.
Ryan Bendure
A&P
RV4 131RB
Rocket reserved 77RM under construction
 
az_gila said:
...are talking about the exhaust pipe, not intake tubes...
See post # 14
Can lifters go bad at some rpms and not others? ...or hot vs. cold?
Click to expand...

Gil,
My post was in response to Steve's post #18 where he could not understand how a stopped engine could have oil running out of the carb.
 
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