Finding a mechanic to lap a valve

[Jsno]

On 7/14/2023 at 6:46 PM, kortopates said:

First i have to disagree that it’s not worthwhile to lap a valve in a high time cylinder. That’s nuts. How to do you suppose Mike B got to 3500 hrs on his engine cylinders? Sometimes the valve can’t be corrected by lapping and the cylinder has to come off for repair but it’s always worth a try to lap it and see if you can correct it. It sure beats pulling the cylinder every day. We’ve found no correlation to worn valve guides causing compression issues or burning of valves, contrary to what many people think. And if your patient you can restore a virtually zero/80 compression, due to leaking exhaust, to 75+/80 cold. It will take a good 15 hrs in service to verify its a winner but who wouldn’t want to try that first.

For how to do it, see Mike’s youtube Savvy Aviation video on valve lapping: 

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I had an engine with low compression,50/80.  The exhaust valve had considerable wobble and would not seat correctly.  Since it wasn't seating it was showing signs of being burned on one part of the edge.  So through my limited experience I believe that a wobbling valve can cause low compression and lead to valve burning/failure.  

[JimB]

17 hours ago, Pinecone said:

Except the shop is not saying to replace the valve.  Or at least one shop.  They are saying to keep flying it until something bad happens.

From what I read, the OP did an oil change, pulled the plugs, borescoped his cylinders, saw something that concerned him and took to a couple mechanics and asked them to lap the valves. They declined and offered some other advice probably(?) based on looking at the pictures and their experience. He went to 2 mechanics and both declined to do the work. 

[JimB]

On 7/14/2023 at 11:41 AM, gdwinc said:

@KSMooniac Thanks for the response.  I should have mentioned that I am a Savvy customer and they provided options for more accommodating shops.  The recommendations were in Grand Junction, CO and Boise, ID so not the most convenient, but doable if there aren't any local Salt Lake area options.

Just out of curiosity, after you borescoped the cylinders yourself, did you send the pictures to Savvy and are they the ones that recommended you have the valve lapped? 

[M20F]

17 minutes ago, JimB said:

Just out of curiosity, after you borescoped the cylinders yourself, did you send the pictures to Savvy and are they the ones that recommended you have the valve lapped? 

Also what is the compression on the cylinder. 

[gdwinc]

40 minutes ago, JimB said:

Just out of curiosity, after you borescoped the cylinders yourself, did you send the pictures to Savvy and are they the ones that recommended you have the valve lapped? 

@JimB Yes, I'm a Savvy customer.  I sent them the pics of all the valves, but I noticed that the exhaust valve on cylinder #4 was asymmetric and pointed it out specifically when I posted the ticket.  They agreed that it looked like a good candidate for lapping. 

@M20F asked about the compression of the cylinder.  This was just an oil change and so a compression test was not completed.  The last compression test was done in March during the annual inspection.  I don't have the log entry in front of me, but I do know that none of the compressions were low enough to be on the "let's keep an eye on this one" list.

[JimB]

45 minutes ago, gdwinc said:

@JimB Yes, I'm a Savvy customer.  I sent them the pics of all the valves, but I noticed that the exhaust valve on cylinder #4 was asymmetric and pointed it out specifically when I posted the ticket.  They agreed that it looked like a good candidate for lapping. 

Mind posting the pic of the valve?

[gdwinc]

Here's a picture of the valve face showing the asymmetry.  I also included a picture of the seat where you can see an inconsistency where the valve is making contact with the seat.

[JimB]

Interesting. I'm not really sure what your concern is. 

[M20F]

I would do a compression test. That is what lapping is designed to fix.  If you are getting low compression and it is leaking out the exhaust lapping the valve can fix that.  If you are getting a solid compression though lapping isn’t going to do anything. 

[kortopates]

26 minutes ago, M20F said:

That is what lapping is designed to fix.

That's part of it. Its also used to correct a valve that is sticking in rotation, creating a hot spot evidenced by a sinusoidal EGT trace. This can correct the issue leading to burning a valve before it burns. Hot spots aren't always accompanied by the sinusoidal EGT but lapping the valve is a proven correction.

Just saying, as I don't actually recall the specifics of OP's valve.

[Fly Boomer]

3 hours ago, kortopates said:

That's part of it. Its also used to correct a valve that is sticking in rotation, creating a hot spot evidenced by a sinusoidal EGT trace.

You obviously know a lot more about this than I do, but I don't see how lapping would help a valve that is "sticking in rotation"?

[EricJ]

5 hours ago, gdwinc said:

Here's a picture of the valve face showing the asymmetry.  I also included a picture of the seat where you can see an inconsistency where the valve is making contact with the seat.

That looks like a very healthy valve to me.    Unless there's a big problem with the compression I'd just keep running that until there was better evidence of a problem.

[MikeOH]

5 hours ago, gdwinc said:

Here's a picture of the valve face showing the asymmetry.  I also included a picture of the seat where you can see an inconsistency where the valve is making contact with the seat.

Damn, that valve looks great.  I'm not seeing the problem...

[A64Pilot]

8 hours ago, Jsno said:

I had an engine with low compression,50/80.  The exhaust valve had considerable wobble and would not seat correctly.  Since it wasn't seating it was showing signs of being burned on one part of the edge.  So through my limited experience I believe that a wobbling valve can cause low compression and lead to valve burning/failure.  

Your absolutely correct and while lapping could possibly mask the problem temporarily it’s not going to actually correct anything.

A valve especially a Lycoming with excessive clearance (wobble) is a verily likely candidate to stick because the excessive clearance will have the oil coke on the stem, It’s more likely in a Lycoming because they are sodium filled valves, the liquid sodium cools the valve largely by dissipating the heat trough the stem and into the head through the guide, so the stem and guide are hotter in a Lycoming than a Conti.

A sticking valve of course can mean the piston contacts the stuck valve and the head breaks off, often this can lead to a destroyed engine. Most don’t but it’s not improbable.

If your going to lap a valve, do a wobble check first, if it fails you need to fix that.

On edit, and I know I’ll get flack from this from the faithful, but a leaking valve is not a normal operating condition, if you have one, you might want to investigate why, very often it’s just a bit of carbon build up and would clear itself very quickly, but staking a valve can also break up the carbon and restore compression, but it’s also likely from worn valve guides. Lapping really doesn’t do much to the hard valve and seat at all, many cylinder shops don’t even lap anymore when they do valve jobs, personally I lap, but not to finish the machining job, your not doing that, but just to ensure I have nice even contact all around as the compound removes just enough of the shiny metal to leave a matt like finish where contact is made.

If you building a performance engine with a three or even a five angle valve job you move the seat to valve contact to the edge of the valve, and you lap to ensure that’s where contact actually is. With a multi angle job your in effect making the valve slightly larger, slightly increasing flow and power, a little. Lapping shows where the contact is.

If you don’t know what your doing and especially if you use anything but the wooden handle with a suction cup, like a drill you can remove metal, and cut a groove into the valve, ruining it.

Quick Google brought this up, it seems it’s a motorcycle forum but they seem knowledgeable.

https://www.dotheton.com/index.php?threads/valve-lapping-for-dummies.28553/

 

 

Edited July 21, 2023 by A64Pilot

[kortopates]

You obviously know a lot more about this than I do, but I don't see how lapping would help a valve that is "sticking in rotation"?

With every opening of the valve, it rotates or turns. The same mechanism of deposits or erosion at the face to seat junction can cause it stop or only partially rotate in a spot rather than rotate freely all through the 360 degrees of rotation.
TCM valves shed most of there heat through the face to seat junction so any failure in rotation causes the area to heat up and a hot spot develops that left unabated will result in a burnt valve. Lapping the valve in situ frees it up to rotate freely and we’ll see the hot spot disappear over time when the stickiness is removed. Of course by cleaning it up it also raises the cylinder compression.

Sticking in rotation should not be confused with the valve stem sticking in the valve guide which causes the valve to stick open a.k.a. lycoming morning sickness which is corrected by reaming out the carbon in the valve guide using the same rope trip. Lycoming valves developing sticking guides because most of heat transfer of their sodium filled valve stems is through the valve stem to guide interface unlike TCM valves. Just trade offs of different designs.

High time cylinders tend to develop wobble in the valve guides but the valve springs do a good job centering the valve face as it closes with what can seem like quite a bit of wobble. As long as the cylinder is functioning fine that’s no reason to pull it unless it makes you sleep better at night.

I have one client with ~3500 hrs on his TCM cylinders that checks his compression and borescopes every oil change. He also laps any valve as soon as it’s getting low (i forget his threshold) or develops a hotspot and it’s enabled him to keep his engine going almost 2x TBO on the same cylinders so far. He was a former porsche mechanic and also laps valves for friends around the airport.


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[M20F]

7 hours ago, kortopates said:

That's part of it. Its also used to correct a valve that is sticking in rotation, creating a hot spot evidenced by a sinusoidal EGT trace. This can correct the issue leading to burning a valve before it burns. Hot spots aren't always accompanied by the sinusoidal EGT but lapping the valve is a proven correction.

Just saying, as I don't actually recall the specifics of OP's valve.

That may be entirely possible.  You would really have to be super smart to be able to see it though.  I see a lot of borescope pictures on the internet.  The good ones are easy to see.  The bad ones are to easy to see.  What you are describing is really hard to see. 
 
If you lap to much the valve isn’t going to seat right either. 

[cliffy]

I agree with EricJ  I don't see too much of a problem from the picture. I see no "green" color indication either. 

BUT if the compression is low AND its leaking at the exhaust valve (listen for it) then even at TBO you might try lapping it. 

If  it doesn't work you are only out a few hrs of labor.  Most of the time it works though but no guarantees. 

I feel it beats jumping right into a cylinder change and the other risks involved with that (case fretting, through bolts and bearing seating) if not done correctly.

Much less invasive.  Just like surgery, less invasive is better. 

Also if so equipped, replace the rotator cap on the top of the valve with a new one a the same time.

If others go bad the next time around then think of some other route. 

But just don't go forward on one indicator. Use them all- low compression, leak at exhaust valve (listen), color design on the valve, use all 3 to make the decision.

I lapped one of my valves 2 years ago (O-360-A1D) and its been good ever since (@150 hrs ago).

TBO to me is not a hard and fast number. Lots of other things go into the overhaul decision.

You might try calling American Aviation down in Page AZ at Lake Powell, right at the Utah border. They operate a fleet of Cessna 207s and do a lot of valve lapping on their airplanes. 

Their shop takes in lots of outside work. I've known them for years and they do a good job. Their owner lives in SLC. 

You might also try to plan a mini-vacation while they do it. Lake Powell is right off the end of the runway.

A fly tour of the lake from KPGA to the old Dangling rope Marina up lake  @25 miles is a great tour loop. 

Plan ahead for a hotel room though. The town fills up in the summer. Car rental right at the airport terminal.

[M20F]

4 minutes ago, cliffy said:

 

TBO to me is not a hard and fast number. Lots of other things go into the overhaul decision.

TBO is only meaningful for to 135.  You can literally have an engine 30K hours over TBO with all new parts that is technically newer/better than an engine 10hrs past TBO.  
 

For a forever plane IRAN is always the way to go but if you ever intend to sell the market is all about TBO

[cliffy]

The market needs an education

Its what goes into an IRAN and how its operated rather than a hard TBO number.

There's nothing magical about the word "overhaul".  There are good ones and there are bad ones. 

An IRAN can be as good or better than an "overhaul". It all depends on what goes into it. 

But alas, most are ignorant of these issues. 

[Pinecone]

22 hours ago, JimB said:

From what I read, the OP did an oil change, pulled the plugs, borescoped his cylinders, saw something that concerned him and took to a couple mechanics and asked them to lap the valves. They declined and offered some other advice probably(?) based on looking at the pictures and their experience. He went to 2 mechanics and both declined to do the work. 

From the original post"

" The other said that it is a lot of labor and his recommendation is to wait for the cylinder to fail a compression test and then replace it."