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Exhaust valve leaking

 
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Coop85



Joined: 11 Aug 2020
Posts: 6

PostPosted: Mon Aug 24, 2020 1:58 pm    Post subject: Exhaust valve leaking Reply with 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


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Marcus Cooper
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Tim Olson



Joined: 25 Jan 2007
Posts: 2823

PostPosted: Mon Aug 24, 2020 2:46 pm    Post subject: Exhaust valve leaking Reply with quote

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




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











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Coop85



Joined: 11 Aug 2020
Posts: 6

PostPosted: Mon Aug 24, 2020 5:54 pm    Post subject: Re: Exhaust valve leaking Reply with quote

Thanks Tim!

As always you are a wealth of helpful information.

Marcus


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Marcus Cooper
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Coop85



Joined: 11 Aug 2020
Posts: 6

PostPosted: Wed Aug 26, 2020 8:49 am    Post subject: Re: Exhaust valve leaking Reply with quote

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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Tim Olson



Joined: 25 Jan 2007
Posts: 2823

PostPosted: Wed Aug 26, 2020 9:42 am    Post subject: Exhaust valve leaking Reply with quote

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




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











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Lenny Iszak



Joined: 23 Mar 2008
Posts: 260

PostPosted: Wed Aug 26, 2020 10:08 am    Post subject: Exhaust valve leaking Reply with quote

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
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bill.peyton



Joined: 19 Sep 2010
Posts: 197
Location: St. Louis, MO

PostPosted: Thu Aug 27, 2020 4:34 am    Post subject: Re: Exhaust valve leaking Reply with quote

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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Coop85



Joined: 11 Aug 2020
Posts: 6

PostPosted: Tue Sep 01, 2020 1:59 pm    Post subject: Exhaust valve leaking Reply with quote

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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