Suggested Engine Cylinder replacement

[mantry]

Howdy, started in on our Annual today and the #4 cylinder (Pilots side middle) only had about 10psi of compression, all the others were in the 68-75 range. The #4 was leaking compression out of the Exhaust pipe.

Question, I would like to get an exchange or an outright cylinder. Our engine is currently mixed with ECI Cermi-Nil on 4 of the 6 and the other 2 including #4 and #2 are ECI Steel. This cylinder has been on the engine I would guess 100 hours or so and has been on about 8 years.

Suggested Vendors for a new cylinder?

Thanks
Mark

[blueldr]

If the cylinder has only about 100 hours on it, why not just grind and reseat the valve? The rings are already worn in.

[Bruce Fenstermacher]

Mark,

If you are saying this cylinder only has 100 hours or it, it is a practically new cylinder. Why would you want to replace it regardless whether it's steel or cerminickel or that you have a mixed batch of them.

What you most likely have is a piece of carbon holding the valve open at this moment. Have you or someone for you done any trouble shooting? A quick inspection with a bore scope would show if there are any glaring issues with the valve and seat. If not or you don't have a bore scope, I'd recommend you run the engine a half hour around the patch and recheck the compression. If it is indeed a ordinary piece of carbon it's likely to be gone and compression good.

There are other ways to clean the carbon and seat the valve which aren't to difficult. Most folks will want to remove the cylinder to clean the carbon and seat the valve but it doesn't have to be removed if you find a mechanic who is very familiar with these engines and comfortable working on the cylinders. I've done about 12 cylinders and not removed one.

[mantry]

Thanks guys for the replies... The Cylinder has been on the plane, I'm guessing about 8 years. I'd have to go back and look to be exact. The plane only flies an hour or so a month(hangered). So I'm guessing that it has about 100 hrs on it. We already have a mixed batch of cylinders, 4 Cerma-Nil and 2 plain steel including this one.

What we have tried so far: First. bounced the valve a couple of times by hitting it with a wooden dowel in case there was just something holding the valve open. That didn't make any difference. Next we removed the rocker arm, placed some clean rope in the cylinder, compressed the valve springs, removed the keepers and the springs. Then pushed the valve in, placed some LAPPING COMPOUND on the valve and then using a piece of rubber house and a drill, attempted to lap the valve in place. It seemed to make a bit of difference in how the valve felt when you rotated it by hand on the seat. Replaced the springs and the keepers after flushing it out with a little bit of solvent. But when we re-checked the compression it had come up to about 25psi but that was it and still leaking through the exhaust. Not sure we have or could find a borescope. I have the cylinder ready to be removed, shroud off, intake off, exhaust off and for the lack of a 9/16" cylinder base wrench, which we couldn't find, would have had it off.

In wiggling the valve stem it seems nice and tight.
There is a local guy that can do cylinder work, but my thinking was instead of having this guy spend time and materials that may, "MAY" exceed the cost of an exchanged/new cylinder, we would just replace/exchange it. But if the opinion is that 100 or so hours and 8 years of being on the plane that it may be the better way to just remove the cylinder and have just this exhaust valve issue looked at closer and/or repaired and then put it back on.

How does that sound?

Thanks in advance.

Mark

PS: Total time on the engine SMOH is about 1080 and was done probably back in about 1993'ish, we bought the plane in 1995 and have put about 600hrs on it since then.

[Bruce Fenstermacher]

Mark,

Sounds like your following all the steps I'd have done except one.

In wiggling the valve stem it seems nice and tight.

Actually a properly fitting valve stem feels looser than you'd think. I'm wondering if this valve stem and guide is just to tight. This actually makes sense being a fairly new cylinder. Before removal I'd want to ream the valve guide and make sure the stem of the valve is clean.

You do this by doing all the steps you did to lap the valve except when the valve spring is off just push the valve all the way into the cylinder. Using safety wire guide the valve back out a spark plug hole and get the stem clean. Get the proper size rem and run that through the valve guide. Clean it all up. The use safety wire to place the valve in line with the guide while you gently use the piston to push the valve back in place. NO NOT FORCE ANYTHING with this method. The valve when alined straight will go right in the guide. Some folks have also tied dental floss to the tip of the valve and used that to pull it back through the guide.

If this doesn't fix the problem the it is probably time for the cylinder to come off for closer inspection. Could be a crack into the exhaust port.

I would not be concerned with the age of the cylinder. Condition is everything. I'd be surprised if any of the cylinders on my airplane are younger than 40 years old but they are in good condition.

[GAHorn]

My concern is "lapping" the valve in situ, with the cylinder still installed. Putting valve lapping compound (an aggressive abrasive) inside an assembled engine really troubles me. I hope you have not started or attempted to actually run that engine, because that compound may seriously damage all the rest of the components in that engine when it circulates with the oil. (Imagine those other cyls, connecting-rod and main bearings, not to mention the gears and OIL PUMP in the accessory case. Running solvent thru that cyl will not likely remove all the compound.)

Therefore, I strongly urge you to completely remove the cylinder and inspect it. THEN you will be better equipped to make a decision whether to REPAIR or replace it. (And the only way to get all that compound out of that engine (presuming it's not been started/operated) is to REMOVE that cylinder.)

(Not mentioned: The wooden-dowel attempt to seat the valve is only effective if that cylinder is on bottom dead center or the rocker is removed. If the cam-lobe is in the up position, even with a collapsed lifter the valve may not fully close. Not meaning to be overly-critical, but out of concern for the selection of the supervising mechanic, the work description mentioned so-far, strongly smacks of amatuerism.)

[c170b53]

The first thing that strikes me is how low the cylinder is, I could see a loss of 20-30 PSI because of carbon but if done correctly that air is just rushing out.

[Bruce Fenstermacher]

My concern is "lapping" the valve in situ, with the cylinder still installed. Putting valve lapping compound (an aggressive abrasive) inside an assembled engine really troubles me. I hope you have not started or attempted to actually run that engine, because that compound may seriously damage all the rest of the components in that engine when it circulates with the oil. (Imagine those other cyls, connecting-rod and main bearings, not to mention the gears and OIL PUMP in the accessory case. Running solvent thru that cyl will not likely remove all the compound.)

I'm not concerned at all about doing this. I've done it to about 12 cylinders on four engines myself. I've then flown those engines for hundreds of hours all over the eastern USA. It's been done to every cylinder on both engines I'm currently running. I do not have an A&P license and work under the direction of a supervising A&P and I've done this with the knowledge of several and not one has voice concern so I don't consider the idea to be way out in left field.

Now having typed the last paragraph I will qualify it. You don't squeeze a tube of lapping compound into the cylinder. (and I don't think George thinks you do). You must work like a surgeon. You must clean the valve and valve seat completely and this is very possible to do very carefully. I will also say that like many things mechanical, there many different opinions and to how to do things, what to do and not to do. If you don't want to or think this is a good idea that is up to you. I'm only relating my positive experience.

[GAHorn]

The first thing that strikes me is how low the cylinder is, I could see a loss of 20-30 PSI because of carbon but if done correctly that air is just rushing out.

I agree. The prospects of a cracked valve seat and/or valve guide or cylinder, or even a damaged valve itself is a distinct possibility. I strongly believe the cylinder should be removed. (and please do not operate it until it has been.)

[W.J.Langholz]

2+2 is adding up to 5 on this one.......I'd take the cylinder off and look see, then you can get it up on the bench and look it over good.

"Peace of Mind" is a wonderful thing


W.

p.s Even George is a "Amatuer" in some circles.I'm learning every day......I just hope I live long enough to be smart some day

[mantry]

Thanks everyone. Yes, the cylinder is coming off and will have a local person who works on cylinders look it over.

Hopefully it will be something that can be done with just that valve and then it can go back in place.

Thanks again. I'll post an update after we find out exactly what it was.