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  #1  
Old 10-31-2020, 07:32 AM
Lan Vinh Do's Avatar
Lan Vinh Do Lan Vinh Do is offline
 
Join Date: Nov 2007
Location: moncton NB
Posts: 237
Default Early exhaust valve failure? Need Advice

Updated

I just did a oil change and clean and gap the sparks plugs. I always use the scope when I remove spark plug. I found something that could look like a beginning of a hot spot on a valve cylinder no 1 ( upper part of the valve on first picture) ?

Engine run fine. Compression is 78. I run on phillips 20-50 and add. cam guard at each oil change since many years. Always update all my flight on savvy analysis and everything is normal.

I need advice on these picture. The last one was taken. in march. 40hre before.
I run 20-40 lean of peak normally at altitude above 6000ft since 2 years.

Is it early sign od exhaust valve failure of just valve that is cleaning up because of the lean of peak operation? What should i do

- Monitor in another 40hre?, do nothing?, immediate action?

Thank You for your advice

PICTURE OF YESTERDAY ( UPPER PART OF THE VALVE ON THE FIRST PICTURE)
LINK TO THE ALBUM. OCTOBER 2020
https://photos.app.goo.gl/kc3jTbMenp1uAF2U6


PICTURE OF MARCH 2020
https://photos.app.goo.gl/qhvhYtPHshb6yhrS8
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RV-7A c-GOSV sold
RV-10 C-GMCE
Rv-7 emp completed but waiting boys to be older to help
donation 2020 done ( little bit earlyer)

Last edited by Lan Vinh Do : 11-08-2020 at 01:25 PM.
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  #2  
Old 10-31-2020, 08:19 AM
carolsyracuse carolsyracuse is offline
 
Join Date: Oct 2006
Location: locust grove, ga
Posts: 140
Default AOPA valve chart

https://www.aopa.org/-/media/Files/A...ster_Final.pdf
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  #3  
Old 10-31-2020, 08:46 AM
Lan Vinh Do's Avatar
Lan Vinh Do Lan Vinh Do is offline
 
Join Date: Nov 2007
Location: moncton NB
Posts: 237
Default Chart

I look at that chart many time.

That is why i want to know if i need to do something now or wait and reassess in 25-40hre would be fine?
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RV-7A c-GOSV sold
RV-10 C-GMCE
Rv-7 emp completed but waiting boys to be older to help
donation 2020 done ( little bit earlyer)
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  #4  
Old 10-31-2020, 08:48 AM
Lan Vinh Do's Avatar
Lan Vinh Do Lan Vinh Do is offline
 
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Location: moncton NB
Posts: 237
Default

I am more concern about the small part that look that it. clear it's deposit and may be a hotter spot. ( upper part on the first picture)
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RV-7A c-GOSV sold
RV-10 C-GMCE
Rv-7 emp completed but waiting boys to be older to help
donation 2020 done ( little bit earlyer)
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  #5  
Old 10-31-2020, 09:42 AM
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KiloFoxtrot KiloFoxtrot is offline
 
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Location: IL
Posts: 33
Default

Just saw this on Superior website. Might help someone.

Email this address and they will send you a link to get access to a free copy of Engine Management 101.

EngineManagement101@SuperiorAirParts.com
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  #6  
Old 10-31-2020, 12:27 PM
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DeeCee 57 DeeCee 57 is offline
 
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Location: LSZF
Posts: 440
Default

Quote:
Is it early sign od exhaust valve failure of just valve that is cleaning up because of the lean of peak operation? What should i do
Sure others are gonna jump in... my take: yes, it looks like a hot spot on the valve which could indeed lead to failure. From your pictures the valve seat looks to be affected as well.
I would:
1) inspect the valve seat for overheating
2) proceed as per stuck valve as in morning sickness, remove the cover and valve spring
3) check for free movement of the valve stem in its guide, ref. SB388C
4) perform a lap job on said valve/seat
5) reinstall, fly a few hours, recheck
6) if not ok, remove cylinder for overhaul/exchange
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  #7  
Old 10-31-2020, 01:08 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by Lan Vinh Do View Post
Is it early sign of exhaust valve failure or just valve that is cleaning up because of the lean of peak operation? What should i do
- Monitor in another 40hre?, do nothing?, immediate action?
Looks like textbook failure, caught early. That sector of the valve was not transferring heat to the valve seat.

What to do? I'd fly five hours and scope it again, because your 78 leakdown says it may have already fixed itself.

If the next inspection looks just a little worse, maybe it can be saved by checking for valve guide sticking, and lapping the valve and seat. The valve guide check is well documented, and some mechanics lap in place while the valve is loose. The conservative approach says pull the cylinder, get the valve under a 10x magnifier, chuck it for a spin with a indicator to ensure the seat is concentric, and really clean out all the grit after lapping.

If gets significantly worse it needs to be replaced. No shortage of opinions, and it's hard to be too conservative.
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  #8  
Old 10-31-2020, 04:12 PM
BillL BillL is offline
 
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Location: Central IL
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Doing the "wobble test" and inspecting the face of the valve would be better done sooner than later. Although the leak down seems good, this burned area is not likely to heal itself. It already got hot, so it isn't some fleck under the face.

2-cents
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Old 11-03-2020, 09:12 PM
sblack sblack is offline
 
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Fir the education of those if us not familiar with how this works, I see the discoloration on the valve and on the seat but what exactly causes it? Is it crud on the valve seat that prevents the valve from making contact with the seat so that it cant transfer heat? It is hard to imagine that there us enough slop in the guide that the valve can stand off in one location and still contact elsewhere but that must be happening.

Does this have anything to do with running lean of peak? Or is it simply carbon or lead buildup?

I guess I need to get a scope. Very good detail on these pictures. A bummer to replace or rebuild a jug, but way better than swallowing a valve. Thanks for sharing.
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  #10  
Old 11-04-2020, 11:47 AM
BillL BillL is offline
 
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Quote:
Originally Posted by sblack View Post
Fir the education of those if us not familiar with how this works, I see the discoloration on the valve and on the seat but what exactly causes it? Is it crud on the valve seat that prevents the valve from making contact with the seat so that it can’t transfer heat? It is hard to imagine that there us enough slop in the guide that the valve can stand off in one location and still contact elsewhere but that must be happening.

Does this have anything to do with running lean of peak? Or is it simply carbon or lead buildup?

I guess I need to get a scope. Very good detail on these pictures. A bummer to replace or rebuild a jug, but way better than swallowing a valve. Thanks for sharing.
It probably has nothing to do with LOP operation. An exhaust valve heats and cools through the combustion cycle. It obviously cools when it sits on the seat, transferring some heat to the seat then head. If it does not seat in an area, then that area will increase in temperature to approach the EGT and higher. Remember, only the expanded gas is measured by the EGT, not the peak. Why did it fail/burn/overheat? Well it could be a number of things, debris does happen, but as the engine ages, the seats get a little wear and not perfectly round, the wear on the valve and do the same, so they have rotators to keep the valve moving. The perimeter of the seat varies in temperature as well and affects the shape and local temps of the valve. We want the valve to experience a time averaged equal temperature around the face, rotators insure that. The semi-circular witness mark around that spot is essentially a constant temperature line where the interior got hot and burned off the face deposits. Only a dimensional inspection of the parts can diagnose the true cause, that is not assured.
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Lord Kelvin:
I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.

Last edited by BillL : 11-04-2020 at 06:54 PM.
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