Question for cylinder head gurus

My friend has been learning to use a boroscope.

He sent me a link to a you-tube video of a valve opening and closing. Please take a look: https://www.youtube.com/watch?v=KxebW7Z6Lwg&feature=youtu.be

If you look closely, you can see slight movement in the valve seat as the valve contacts it. I think it is oil that is squeezing out of the seam between the seat and the cylinder head.

I would have thought the seat should be pressed into the head tightly and shouldn't move.

Is this bad? OK? typical?

Should this be addressed immediately? Soon? Let it go until something bad happens?

Its not pretty when a seat pops loose. They have an interference fit and shouldn't leak.

Seems not okay - not typical.

Personally, I wouldn't fly the aircraft until this is resolved.

FWIW.

Dan

That is a failure waiting to happen.

Keith

First it is loose when cold, then it is loose when hot. That's bad.

I know of one engine was highly turbocharged and had a tapered shape on the seat, it was chilled in then a die pressed on the head to yield material on the seat. It was the only way it could be made to stay in place. I don't think this applies to the NA-Lyc.

How many hours on this head assy? Maybe now is a good time to have a new (oversized) seat installed.

Edit - nice clear picture with that scope - what specs does it have?

Ya that was my question - what borescope is that?

Sucks to find that, but very good to find that on the ground before a lot of collateral damage to the engine or worse. I think I need a borescope. Sorry can't offer any wisdom.

scsmith said:

My friend has been learning to use a boroscope.

He sent me a link to a you-tube video of a valve opening and closing. Please take a look: https://www.youtube.com/watch?v=KxebW7Z6Lwg&feature=youtu.be

If you look closely, you can see slight movement in the valve seat as the valve contacts it. I think it is oil that is squeezing out of the seam between the seat and the cylinder head.

I would have thought the seat should be pressed into the head tightly and shouldn't move.

Is this bad? OK? typical?

Should this be addressed immediately? Soon? Let it go until something bad happens?

Click to expand...

It appears the valve guide is worn, I wouldn't call it critical. There lots of this out there on high time engines. Is it good?, no.

8 ball said:

It appears the valve guide is worn, I wouldn't call it critical. There lots of this out there on high time engines. Is it good?, no.

Click to expand...

That's my impression also. the rocking motion of the valve in the worn guide is causing uneven pressure on the seat.I've seen this failure in type IV VW cylinder heads that are run hot.Great work with the bore scope in finding this early.May I ask how many hours and who's cylinders are these?What oil are you using? The guide wear is common issue,the seat movement is not.I wouldn't fly it till the jugs are pulled and sent out for repair.A loss of one cylinder in a Lycoming will spreed debris to the other 3.Much cheaper&safer to Top this engine now.IMHO
RHill

Seat Movement

8 ball said:

It appears the valve guide is worn, I wouldn't call it critical. There lots of this out there on high time engines. Is it good?, no.

Click to expand...

The valve seat should not be moving. Period!

Skylor

Valve seat/ guide

Looks like a combination of both a worn valve guide and a loose seat. I certainly wouldn't fly it until I resolved the issue. The cost of an overhauled or new cylinder is minimal compared to potential damage if left unresolved!

skylor said:

The valve seat should not be moving. Period!

Skylor

Click to expand...

Can't imagine thinking differently! My engine was acting funny at startup, but only sometimes. I found movement in one of my seat on the offending cylinder. Pulled the cylinder, reached in and pulled the seat out with my fingers. Was a cracked head. Turned into an overhaul based on other things.

thanks for all the replies

Thanks everyone.

I don't have any specific knowledge of the particulars. My friend has a Cirrus, but he also uses the boroscope to look inside other engines for friends. So I don't know if this is his or someone else's.

I can ask him about the brand/specs of the boroscope. I'll post back here.

These are on you-tube, so if you would like to see more, there are a couple more. One of the others is definitely a valve-guide wear example-you can see the valve shift sideways as it seats. two others show other valve seats moving.

In the one I linked to, I disagree that there is valve-guide wear. It pretty clearly looks like the valve does not move laterally as it contacts the seat, it moves straight into the seat, and then the seat squirms a little because it is loose in the cylinder. It is kind of a moot point though, a new cylinder will fix both issues.

The very best part of this story is that without the boroscope inspection, one would have no indication of anything wrong here, and would run the engine until something failed. This kind of periodic inspection seems very valuable.

But I wonder.....how many engines are out there with slightly loose guides like this, and might run for a long time, maybe even to TBO, and how would anyone would know? I think that this inspection is not widespread, and so there is very little data. But this winter I hope to get my friend up here with that scope to take a looke at mine.

More info

In case anyone is interested (a few expressed interest) here are more particulars on the engine in question, and the borescope.

First, the borescope is a Snap-On BK8000. My friend said that it is difficult to see minor things like this looking at the display because of screen glare. He recommends wearing a black shirt and closing hangar doors. But the best thing to do is record the images and view playback on a computer.

The engine is an IO-550 in a Cirrus SR-22. It was a factory-new engine with now 1700 hrs total time.There are no running symptoms that would indicate a problem.

He has been doing borescope inspections every other oil change for several years. Early this year, he observed one very slightly loose valve seat, and decided to monitor it over time. At the latest inspection (most of a year since first discovery) that seat had become noticeably more loose, and two other cylinders now show slight looseness of the seats.

The engine is getting a top-end overhaul now. The shop said that they do see this from time to time. Sometimes when they turn the cylinder upright the seat falls out.

Just think how many thousands of aircraft engines are out there that never get this type of borescope inspection! How many have slightly loose seats and run until some other issue requires cylinder change? How many run until the seat falls out while the engine is running and breaks a valve off?

Is this something more common to Continentals than Lycomings? Is there something unique about the design of the seat that makes it prone to loosening? Given the absence of inspection protocol for this issue, there is just no meaningful data.

I'm going to borrow my friend's borescope and take a look as soon as I can.

I had an intake valve seat come clear out of its machined cavity, and it got cocked a bit sideways and prevented the valve from closing/sealing off the combustion chamber. This made for an extremely rough running engine

Luckily, it happened as I pulled the power back to land---on a flight to San Antonio in my old Stinson.

Franklin 165 engine, so it is not just a Lyc or Conti issue. I suspect any engine with a steel seat inserted into an alum head is a candidate for this kind of thing.