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Is 'normal' exhaust flange blow by such a thing?

L

llaux

Member
All four of the exhaust flanges on my IO390EXP119 engine have a minimal amount of grey residue on the cylinders where the exhaust pipes attach to the bottom of the cylinders.

I've checked the torque on all the nuts and have been using the lock washers as well (checked torque at least 3 or 4 times since new -- engine now has 50 hours on it). Oh and I'm using the Lycoming 77611 gaskets.

I had an A&P look at it in person and was told that this amount of exhaust gas blow by was 'normal'.

A photo of one of the areas in question is attached.

I wanted to see if this group had any thoughts!

Thanks!!
 

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llaux said:
All four of the exhaust flanges on my IO390EXP119 engine have a minimal amount of grey residue on the cylinders where the exhaust pipes attach to the bottom of the cylinders.

I've checked the torque on all the nuts and have been using the lock washers as well (checked torque at least 3 or 4 times since new -- engine now has 50 hours on it). Oh and I'm using the Lycoming 77611 gaskets.

I had an A&P look at it in person and was told that this amount of exhaust gas blow by was 'normal'.

A photo of one of the areas in question is attached.

I wanted to see if this group had any thoughts!

Thanks!!
Click to expand...

Hard to tell it looks pretty clean. I had a large amount leaking past the gasket and I took the flange and got it on a bench vise to bend the flange into position. It had warped over time.
 
Interesting -- This may or may not be anything, but the portion of the gasket material that's visible in the picture doesn't look like the Lycoming 77611 part.
 

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If it is leaking, the flange boss is eroding. Might be “ok” for some indeterminate amount of time but cylinder parent metal is being affected. It can cause the need to:

Remove studs and lap the flange in place
To
Weld repair and remachine the base.

Not sure how acceptable leakage is defined. At a minimum, drop the exhaust, inspect, lube the exhaust joints for good freedom of movement, reinstall slowly with new blow-proofs. A rubber mallet is helpful to bump through any stick-tion/binding. Good luck
 
There should be NO leak at the flange.

There most likely will be light tan blow-by from the slip joints all over the low pressure (bottom) side of the engine.
 
Freemasm said:
If it is leaking, the flange boss is eroding. Might be “ok” for some indeterminate amount of time but cylinder parent metal is being affected. It can cause the need to:

Remove studs and lap the flange in place
To
Weld repair and remachine the base.

Not sure how acceptable leakage is defined. At a minimum, drop the exhaust, inspect, lube the exhaust joints for good freedom of movement, reinstall slowly with new blow-proofs. A rubber mallet is helpful to bump through any stick-tion/binding. Good luck
Click to expand...

Okay, I can do the 'minimum' next steps you listed relatively easily. Will start working on that. Quick follow up: how does one clean off the existing leakage residue so that you can see if the leak was fixed or not by starting with a clean surface?
 
Exhaust

Who is the exhaust manufacturer? The nut and washer are partially on the weld and that does not help. Also prevents obtaining proper torque on nuts. Not standard protocol but a simple fix would be to grind clearance for the weld on a flat washer, install that washer then the lock washer.
Some exhaust manufacturers are using a slip joint close to the cylinder to allow the flange to properly align with the exhaust port.
Warped exhaust flanges form welding could also be an issue.
Alternatively you could counterbore the weld for clearance for the nut/washer.
 
Interesting that the nut and lock washer overlaps the weld on that flange. That may be ok but not sure that provides the best pull up on that flange and gasket.
 
DennisRhodes said:
Interesting that the nut and lock washer overlaps the weld on that flange. That may be ok but not sure that provides the best pull up on that flange and gasket.
Click to expand...

I had an aircraft with that issue. We used a regular washer, ground down, so there was a flat surface for lock washer and nut. Not ideal.

I have never heard of “normal” exhaust flange leaks.
 
Exhaust leak

As a previous poster commented there does NOT appear to be a gasket in the picture provide. Also check the exhaust flange with a straight edge for being flat. I have had to have several RV exhaust machined flat again after leaks were found. Of course I don't need to tell you that being exposed to Exhaust is harmful to you. My 2cents!
 
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Should the exhaust ports need resurfacing, there are several tools available that will enable you to resurface the exhaust ports with the cylinders in place.
 
bjdecker said:
Interesting -- This may or may not be anything, but the portion of the gasket material that's visible in the picture doesn't look like the Lycoming 77611 part.
Click to expand...

+1

Looks like the preferred gasket is not installed. There are several varieties. The one in brians pic is the blow proof gasket. It is a MUCH better design and far less likely to leak. It does appear that yours is leaking, but tough to say how much.
 
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llaux said:
Okay, I can do the 'minimum' next steps you listed relatively easily. Will start working on that. Quick follow up: how does one clean off the existing leakage residue so that you can see if the leak was fixed or not by starting with a clean surface?
Click to expand...

There is no reason to think there is anything wrong with your flanges yet. Better to pull it off and examine for any issues. Clean with solvent and razor blade carefully. Report any issues observed and we can provide suggestions.
 
The question is " is exhaust flange blow by normal"
Under no conditions is blow by around or through an exhaust flange normal. EVER. It's called a leak for a reason.
Find out if, why, and how, and fix it now or suffer the consequences of not.
Good catch to see it before it causes major damage to the head face.
My luck varies Fixit
 
bjdecker said:
Interesting -- This may or may not be anything, but the portion of the gasket material that's visible in the picture doesn't look like the Lycoming 77611 part.
Click to expand...

Y'all had me worried that I didn't install the correct gasket! As you can see in the attached photo, the (newer?) version of the Lycoming 77611 gasket is no longer gold/brass in color. The ones in the photos are the exact same as I've got installed.
 

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llaux said:
Y'all had me worried that I didn't install the correct gasket! As you can see in the attached photo, the (newer?) version of the Lycoming 77611 gasket is no longer gold/brass in color. The ones in the photos are the exact same as I've got installed.
Click to expand...

"New" happens :)

What's the material - Metal or some funky-fiber?
 
Small bead of ultra copper RTV on both sides of a blo-proof gasket will create a gas-tight seal and prevent exhaust leakage by filling in the voids in the tool marks. Also helps hold the gaskets in place while manipulating the exhaust into position.
 
rocketbob said:
Small bead of ultra copper RTV on both sides of a blo-proof gasket will create a gas-tight seal and prevent exhaust leakage by filling in the voids in the tool marks. Also helps hold the gaskets in place while manipulating the exhaust into position.
Click to expand...

Sounds like a good piece of advice for some additional protection against leaking.

Thanks again everyone for your input.
 
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