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  #1  
Old 08-13-2022, 02:05 AM
david.perl's Avatar
david.perl david.perl is offline
 
Join Date: Dec 2010
Location: Watford UK
Posts: 154
Default need help interpreting borescope for leaking exhaust valve

I posted a couple weeks back in the engine section about a presale that picked up a leaking exhaust valve.

I am hoping perhaps a wider audience will read this as opposed to my OP which is buried deeper.

Long story short, compression on cylinder 1 was 68 cold, dropped after flying hard for 90 mins to 58.

Engine is lycoming IO360 M1b with 400 hours over6 years

I borrowed a friends borescope and posted a link, problem was i was looking at the intake valve and the camera was not great so hard to analyse.

I purchased a HD model of the Ablescope 400 - much better images now. Ive uploaded them to my youtube. Are there any experienced folk here that can give an opinion? I Am also waiting to see if SavvyQA includes borescope analysis and will join that if it does.

Link is here
https://www.youtube.com/watch?v=YkNg6kTYvRY

thanks in advance for any thoughts.
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Last edited by david.perl : 08-13-2022 at 09:42 AM.
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  #2  
Old 08-13-2022, 03:04 AM
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Dan 57 Dan 57 is offline
 
Join Date: Sep 2018
Location: LSZF
Posts: 1,101
Default

Hi David
What I see, in a nutshell:
- piston, cylinder wall, intake valve, all look normal
- the exhaust valve has a hot spot

Due to the waggly movie it is difficult to diagnose more with certainty.
At this stage you would have to inspect the seat of the valve, the surface of contact, for a continuous ring. Turn the prop until the exhaust valve is fully open, and then try to inspect the circumference to the seat, specifically the contact area... I suspect that, on what is the bottom of the valve in the vid e.g. the hot spot, you will find the ring of contact broken...

If this is confirmed, a in situ lapping of the valve, and a replacement of the rotator cap, might, repeat, might, save the day. Also make sure the valve rotates freely in its guide (a read of SB388C might be worth). We've had limited success using this procedure.
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  #3  
Old 08-13-2022, 04:02 AM
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rv8ch rv8ch is offline
 
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Default

The new VA400 looks much better than my old version - impressive quality.

As Dan mentioned, I think photos are easier to interpret, and we need to see the seat.
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  #4  
Old 08-13-2022, 05:28 AM
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david.perl david.perl is offline
 
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thanks for the responses so far

ive taken a few screen grabs and will go down tomorrow to try and get some clearer photos of the valve seat - it seemed hard to get all around the cylinder.
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  #5  
Old 08-13-2022, 06:28 AM
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DanH DanH is offline
 
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Pixelation makes it hard to be sure, but there may be a crack between the valve seats.
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  #6  
Old 08-13-2022, 07:09 AM
riobison riobison is offline
 
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Location: Oliver BC & Red Deer Alberta Canada
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Default Soapy water

Quote:
Originally Posted by DanH View Post
Pixelation makes it hard to be sure, but there may be a crack between the valve seats.
Yes, I agree. It certainly looks like it. Put some air to it and spray some soapy water to it. If the crack is there you will have bubbles. Thats how I found mine a few years ago.
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  #7  
Old 08-13-2022, 07:55 AM
abuura abuura is offline
 
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Quote:
Originally Posted by david.perl View Post

...leaking exhaust valve.

Long story short, compression on cylinder 1 was 68 cold, dropped after flying hard for 90 mins to 58.
How did you ascertain that it's that valve leaking? I do agree the pictures you posted tend to show a hot spot, but I'm not sure what that would have to do with air escaping at that location.
See below for some data I experienced the last year (Mattituck TMO-360). I was really sweating the differential pressure(s), planning to do a ring flush - maybe even pulling the jug, and then the last results came up...
My point is keep flying, keep imaging/measuring, monitor.

1340.4 63 66 71 73
1355.5 65 68 72 75
1359.5 65 73 68 69
1383.8 71 71 75 74
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  #8  
Old 08-13-2022, 08:45 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by david.perl View Post
thanks for the responses so far

ive taken a few screen grabs and will go down tomorrow to try and get some clearer photos of the valve seat - it seemed hard to get all around the cylinder.
In the last pic, you can see a small white piece of debris that is stuck to the valve sealing face. It is perfectly centered in the hot spot. That is likely causing the valve to not fully seat in that area and hence cannot shed heat in that area, causing the burning of the valve in that area. I would take steps to get rid of it. Do some reseach - hammer taps on stem, in situ lapping, etc. I would not keep flying and looking, as the valve may still be salvageable, but continued overheating will cause it to warp and require a new valve. That said it may already have gotten to that point.

Definitely investigate the white line between the seats as it looks suspiciously like a crack.

Larry
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Last edited by lr172 : 08-13-2022 at 08:54 AM.
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  #9  
Old 08-13-2022, 10:23 AM
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david.perl david.perl is offline
 
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Default

re how could we tell if is from the exhaust - we could hear air escaping from the exhaust and nothing from the oil or intake areas.

We've also tapped the exhaust valve with a rubber hammer - made no difference

Ive signed up to SavyQA to see what they say
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  #10  
Old 08-13-2022, 11:05 AM
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BillL BillL is offline
 
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Location: Central IL
Posts: 6,849
Default If it was me . . .

Quote:
Originally Posted by david.perl View Post
re how could we tell if is from the exhaust - we could hear air escaping from the exhaust and nothing from the oil or intake areas.

We've also tapped the exhaust valve with a rubber hammer - made no difference

Ive signed up to SavyQA to see what they say
If you had the rocker off, or ensured there was lash and tapped the valve and still leaked and triple checked to ensure it is this valve leaking.

Then "if it was me" I would - remove the rockers, remove the spring, ensure guide is not tight, video (crystal clear) the face of the valve (360 deg), prussian blue the valve to see if the seat and valve have full contact (don't rotate), then consider lapping in situ. Remove exhaust pipe as needed for access and inspection.

FYI On other brands, I have had a leaking valve that frosted the seats when lapping 360 deg and found that oval seat+oval valve can contact when rotated and still leak. IMO, lapping is only good to remove debris to allow a good valve/seat to fully contact, not to repair erosion/wear.

Insert inspection to verify head is not cracked. If the valve has been leaking a while . . . the leaking exhaust gas will over heat/expand the seat and stress the head. If lapping does not completely seal then it is time to move to more invasive measures.

Now, if you are employing Savvy and a mechanic ($); it is best that to follow their direction for their support in the final outcome. But do let us know the outcome.
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