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Exhaust valve leaking

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Coop85

Joined: 11 Aug 2020
Posts: 17

Posted: Mon Aug 24, 2020 1:58 pm Post subject: Exhaust valve leaking

I have a clear leak in one of my exhaust valves while doing a compression check.  The odd thing is I seem to have normal power and the temperatures are all consistent with the other cylinders.  Just curious if anyone has had this and any easy solutions?  I've read a few links about sticky valves and a rope method to help free them but I'm curious if there are other thoughts.



Thanks,

Marcus

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_________________
Marcus Cooper
RV-10 since 2006

Tim Olson

Joined: 25 Jan 2007
Posts: 2878

Posted: Mon Aug 24, 2020 2:46 pm Post subject: Exhaust valve leaking

Hi Marcus,



A couple things...



The rope method is just about getting the valve spring off, as far as I 

know.  I don't think it's actually useful to help unstick a valve.

And of course valves can be sticky, or wobbly...likely not both

at the same time.



What you probably have going on is just a bad seating of the valve

that's causing it to leak.  I dealt with that this spring, and found

it really isn't that hard to fix, or inspect, as long as you've got

the tools.



You will need a valve spring compressor tool for sure.

The one I have is this one:



https://www.aircraftspruce.com/catalog/topages/compressor.php?clickkey=8804



It's also helpful to have a little light. Either a flashlight into

the cylinder, or one like this:



https://www.amazon.com/gp/product/B00008BFS6/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1



You can do it without dropping the exhaust, if you wish.  I have a

friend who may jump in on the discussion who just started this on

his engine yesterday. He dropped his exhaust. I didn't.



As a side note, I got a rocker arm removal tool that compresses the

springs, and my buddy tried his yesterday and didn't like it.

Certainly a made-for-the-task tool to compress both springs would

make the job a piece of cake.



At any rate, you basically just remove the rocker cover, then

remove the rocker arm from the exhaust valve side, and then

remove the valve spring (using the rope trick) and then you

will be able to push the valve into the cylinder far enough that

you can spin it with your fingers and inspect the seating surface.

If it's seating all the way around it should be pretty uniform

looking of a darkened stripe around the valve seat where it makes

contact.  If it's got lighter patches, or a narrowing in an area

of the valve, then it's probably just leaking in that spot a little.



To get that seat restored to a nice full seat, you can lap the valve,

right in place.  This article is one I found when I was reading on it

and I found it helpful.



https://www.tennesseeaircraft.net/2011/11/13/exhaust-valve-lapping/



There are other good articles out there as well.



Anyway, now that I know how to do it, it's a job that I could

probably get completed in an hour or so.  I had slightly low

compression (around 65) on one valve and saw the seat had one area

where the seating wasn't perfect.  After lapping it for a short

time, I was able to clean it up and did a cold compression test

and it was >75.  I flew it to warm it up, and compression was

back in the normal 77-79 range and stayed there after that.

I know what they say, that compression in the 60's can be

OK on a lycoming, but I would think if you have an outlier on

your engine, you will do yourself a favor if you just deal with

it early, so the seat doesn't get additional erosion.



Hopefully that gets you on the right track to get started.

You can probably see it with a good inspection cam without

pulling the valve spring, but I find that you can get a perfect

view if you just do the little extra work to get that far.



Regarding your comment about normal power and temps, let me

tell you this:   I had a worn valve guide on one cylinder

and the valve would barely hold any compression at all.

I was shocked that I even had an issue, because when I did

the warm up flight before the compression test, I watched

my EGTs and CHTs closely and everything ran just fine. Power

felt good, engine was smooth.  Nothing identifiable. Then

I did the compression test and found that one valve at 65-ish

and the other way lower, and about had a heart attack.

That's when I learned to lap the one valve, which took care of

it completely, but the other required a new valve guide, done

by a professional shop. They turned it around in 2 days and

did a fantastic job, but they showed me the valve from the

inside of the cylinder perspective before they fixed it, and

it was so wobbly that I don't know how it could have seated.



What that experience told me is that these engines really

won't feel very different, even if you have a big leak.

There was no sign that I could find, at least without paying

close attention.  I did find during diagnosis that if I

pulled the mixture back WAY far on the ground for a run-up

I could actually see that one cylinder depart from the others

a little in how the EGTs looked, but you really had to look

hard at it, and that was a real bad leak.  So if you have

just a minor reduction in compression, you're probably not

going to have a clue, even with a good engine monitor.



Another side note:  Actual A&Ps told me to just put

Marvels Mystery Oil in it and fly it hard.  While I understand

their perspective, I'm not the type to just do something

so crude, when I can do a little more work and figure out

the actual issue.  That's what led me to learning how to

lap the valve.  And, I thought I just had to lap 2 valves

and I'd be all set, but it was very obvious when I pulled

that spring off the very bad compression cylinder that the

valve guide was shot.  So I'm glad I didn't just listen

to the MMO tip and go on my way.  All the other valves

were both seating well, and had valve guides that had

much more normal clearance, so in the end, all was real good.



One final tip.  If you do take off both rocker arms,

make sure you set aside your intake and exhaust rockers

and pushrods in separate places so you get them back

properly on the right position.  On many engines, the

only rocker arm with an oil passage is the exhaust rocker.

You want that to get back on that valve. And, the pushrods

are tuned by length, so don't mix them up or you may get

valves that don't open the amount that they were originally

set up for.

Sorry that got long, but there's a lot of info in there to

chew on.



Tim



On 8/24/20 4:58 PM, Coop85 wrote:

 	  Quote: 	
		   

 

 I have a clear leak in one of my exhaust valves while doing a compression check.  The odd thing is I seem to have normal power and the temperatures are all consistent with the other cylinders.  Just curious if anyone has had this and any easy solutions?  I've read a few links about sticky valves and a rope method to help free them but I'm curious if there are other thoughts.

 

 Thanks,

 Marcus

 

 --------

 Marcus Cooper

 RV-10 since 2006

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=497956#497956

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Coop85

Joined: 11 Aug 2020
Posts: 17

Posted: Mon Aug 24, 2020 5:54 pm Post subject: Re: Exhaust valve leaking

Thanks Tim!



As always you are a wealth of helpful information.



Marcus

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_________________
Marcus Cooper
RV-10 since 2006

Coop85

Joined: 11 Aug 2020
Posts: 17

Posted: Wed Aug 26, 2020 8:49 am Post subject: Re: Exhaust valve leaking

Tim,



Thanks again for the info. Unfortunately by work environment is poor at best so I’m hoping to minimize trips to the airplane. Lazy question, but any chance you recall what size tubing you got to grab the valve for the lapping procedure?



Thanks,

Marcus 



 	  Tim Olson wrote: 	
		  

To get that seat restored to a nice full seat, you can lap the valve,

right in place.  This article is one I found when I was reading on it

and I found it helpful.



https://www.tennesseeaircraft.net/2011/11/13/exhaust-valve-lapping/

 

	
[/quote]

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_________________
Marcus Cooper
RV-10 since 2006

Tim Olson

Joined: 25 Jan 2007
Posts: 2878

Posted: Wed Aug 26, 2020 9:42 am Post subject: Exhaust valve leaking

I can’t remember for sure which tubing but I measured my valve stem at .498” give or take a little.  So probably get some with 1/2” ID but also one step smaller just in case.  You can also chuck it in a drill too.

Tim

 	  Quote: 	
		   On Aug 26, 2020, at 12:00 PM, Coop85 <cooprv7(at)yahoo.com> wrote:

 Tim,

 Thanks again for the info. Unfortunately by work environment is poor at best so I’m hoping to minimize trips to the airplane. Lazy question, but any chance you recall what size tubing you got to grab the valve for the lapping procedure?

 Thanks,

 Marcus 

 Tim Olson wrote:

> 

> To get that seat restored to a nice full seat, you can lap the valve,

> right in place.  This article is one I found when I was reading on it

> and I found it helpful.

> 

> https://www.tennesseeaircraft.net/2011/11/13/exhaust-valve-lapping/

> 

> 

> 

> 

 --------

 Marcus Cooper

 RV-10 since 2006

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=497999#497999

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Lenny Iszak

Joined: 23 Mar 2008
Posts: 270

Posted: Wed Aug 26, 2020 10:08 am Post subject: Exhaust valve leaking

1/2” ID.

This setup works well, see attached photo.

Lenny

 	  Quote: 	
		  > On Aug 26, 2020, at 1:02 PM, Coop85 <cooprv7(at)yahoo.com> wrote:

 

 

 Tim,

 

 Thanks again for the info. Unfortunately by work environment is poor at best so I’m hoping to minimize trips to the airplane. Lazy question, but any chance you recall what size tubing you got to grab the valve for the lapping procedure?

 

 Thanks,

 Marcus 

 

 

 Tim Olson wrote:

> 

> To get that seat restored to a nice full seat, you can lap the valve,

> right in place.  This article is one I found when I was reading on it

> and I found it helpful.

> 

> https://www.tennesseeaircraft.net/2011/11/13/exhaust-valve-lapping/

 

 --------

 Marcus Cooper

 RV-10 since 2006

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=497999#497999

 

 

 

 

 

 

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Lenny Iszak
Palm City, FL
2014 RV-10, N311LZ - 500 hrs

bill.peyton

Joined: 19 Sep 2010
Posts: 198
Location: St. Louis, MO

Posted: Thu Aug 27, 2020 4:34 am Post subject: Re: Exhaust valve leaking

Before you go through all the trouble of lapping the valve, do yourself a favor and borescope the cylinder to take a look at the valve.  It could very well be overheated in some portion of the circumference  and need to be replaced.

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_________________
Bill
WA0SYV
Aviation Partners, LLC

Coop85

Joined: 11 Aug 2020
Posts: 17

Posted: Tue Sep 01, 2020 1:59 pm Post subject: Exhaust valve leaking

Thanks again for all of the guidance. 

Turns out a 7/16” hose works quite well. I should have tried the drill but honestly forgot in the heat of the moment. 

My borescope is poor and gave up on me before I could make a valid assessment, but the valve seems intact from all I could tell. I lapped the valve and it went from a gritty sound to smooth so I thought I had done the trick. Unfortunately the poor mans compression check (pulling it through), as I’m away from my hangar, had disappointing results. I may try one more time before handing it over to the experts. 

Thanks again,

Marcus 

 	  Quote: 	
		   On Aug 28, 2020, at 03:00, Tim Olson <Tim(at)myrv10.com> wrote:

 I can’t remember for sure which tubing but I measured my valve stem at .498” give or take a little.  So probably get some with 1/2” ID but also one step smaller just in case.  You can also chuck it in a drill too.

 Tim

>> On Aug 26, 2020, at 12:00 PM, Coop85 <cooprv7(at)yahoo.com> wrote:

>> 

>> 

>> 

>> Tim,

>> 

>> Thanks again for the info. Unfortunately by work environment is poor at best so I’m hoping to minimize trips to the airplane. Lazy question, but any chance you recall what size tubing you got to grab the valve for the lapping procedure?

>> 

>> Thanks,

>> Marcus 

>> 

>> 

>> Tim Olson wrote:

>> 

>> To get that seat restored to a nice full seat, you can lap the valve,

>> right in place.  This article is one I found when I was reading on it

>> and I found it helpful.

>> 

>> https://www.tennesseeaircraft.net/2011/11/13/exhaust-valve-lapping/

>> 

>> 

>> 

>> 

> 

> --------

> Marcus Cooper

> RV-10 since 2006

> 

> 

> 

> 

> Read this topic online here:

> 

> http://forums.matronics.com/viewtopic.php?p=497999#497999

> 

> 

> 

> 

> 

> 

> 

> 

>

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Marcus Cooper
RV-10 since 2006

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