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obnoxious exhaust valve

dougknight

Well Known Member
Over the last six years I have watched #3 cylinder digress from 78/80 to 67/80 on the leak down test of my 0-320-D1A. Approximate hours of this range is 500 hrs TT in 2015 to 800 hrs TT in 2021. I always listen very closely at oil fill spout, air breather intake and exhaust as each cylinder is under pressure. #3 has been obnoxiously loud out the exhaust for the last 300-400hrs.
I'm thinking the trend is obvious and it is time to attempt lapping the exhaust valve before it gets worse. Just wondering what the brain trust would do.

doug knight
RV-9a , 90625
 
Over the last six years I have watched #3 cylinder digress from 78/80 to 67/80 on the leak down test of my 0-320-D1A. Approximate hours of this range is 500 hrs TT in 2015 to 800 hrs TT in 2021. I always listen very closely at oil fill spout, air breather intake and exhaust as each cylinder is under pressure. #3 has been obnoxiously loud out the exhaust for the last 300-400hrs.
I'm thinking the trend is obvious and it is time to attempt lapping the exhaust valve before it gets worse. Just wondering what the brain trust would do.

doug knight
RV-9a , 90625

first thing I would do is to bore scope it, see what the condition on the valve is. if it shows a hot spot or not. if the valve has a good heat pattern, then it might be worth lapping it, but if it shows a hot spot I would be leaning towards a cyl overhaul or a new cyl. same for showing signs of erosion on the edge.

bob burns
RV-4 N82RB
 
VA-400-WiFi Bundle: Vividia Ablescope VA-400 USB Rigid Articulating Borescope Plus VA-B2 WiFi AirBox for iOS Tablets iPhone and Android Phone and Tablet.

If you use an apple device, this bundled or similar adapter is needed, for Android or Windows laptop, not needed if On-the-Go (OTG) works on your Android.
 
Quick search on Bore scope and Tim Holmes you sold me. Going with the Teslong #Nts500b over the vivida 400. $135.99
 
any suggestions on best lapping compound?

ok, quick search and this seems pretty generic stuff. will go with loctite #1777012 280 grit 20 oz from amazon for $10.59 unless I hear of better
 
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Just an FYI

Quick search on Bore scope and Tim Holmes you sold me. Going with the Teslong #Nts500b over the vivida 400. $135.99

I recommended this to my 10-Friend and it has much better resolution, but he was not totally happy with the lack of ability to point it where he wanted to see. I have the teslong borescope for firearms and it has fantastic resolution compared to my VA- 400. I just wish it had the high resolution of the Teslong. Too bad they can't be combined, after all it's just a camera with a wire isn't it?

I still think for this job resolution would be a big advantage for seat inspection.

Be sure you really clean well to remove all traces of abrasive.
 
I would not lap a valve until I knew why it was leaking. Several reasons for a leaking exh valve and not all can be resolved with simply lapping the interface.
 
Leaking Exhaust Valve in Cylinder #3

Cylinder #3 seems to be the hardest cylinder on exhaust valves and guides due to heat and restricted top end oil flow on that side of the engine. I would look carefully at the valve as it seats and see if you don’t notice a slight sliding of the valve as it closes. This tells you the guide is worn excessively and likely your problem. Unfortunately the only way to remedy this is pull the cylinder for repair.
 
numbers posted were hot...this year. some years have been cold with similar down trending values over the years.

thanks for al the suggestions. Bore scope supposed to be in the mail tomorrow!
 
wobble test?:)
IMG-3169.jpg
 
a couple photos of the culprit. Leave it alone and run it? Try lapping it in place? Pull the whole jug? Suggestions welcomed.
 

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a couple photos of the culprit. Leave it alone and run it? Try lapping it in place? Pull the whole jug? Suggestions welcomed.

It does not look like it has a good seal or the carbon buildup on the valve and the seal match perfectly. Do your other valves look the same? Recent videos from Mike Busch seem to suggest "do nothing" if the power output is fine, but there seems to be little risk in lapping if you do it right (like most things in life).
 
I would "Stake" the valve, and run it for a while, then do a compression leak-down test. The valve doesn't look all that bad.

I believe that Lycoming has instructions on how to Stake a valve. It's pretty easy.

If I can find the Staking instructions, I will post them here, but I'm betting someone will beat me to it! :eek:
 
a couple photos of the culprit. Leave it alone and run it? Try lapping it in place? Pull the whole jug? Suggestions welcomed.

Looks like at least 3-5 thou of deposits on the seat and therefore 3-5 thou of clearance. If the valve was touching the seat in that spot, the deposits wouldn't be there or at least would be shinny, not matte. Seems quite unlikely that lapping will resolve that type of fit up problem, especially given the fact that you will struggle to get good pressure when working from the stem. Lapping is typically done from the valve side, not the stem side, as you must get a good amount of even pressure at the interface point. Moot anyways if the reason for the poor fitting is due to a worn valve guide or bent valve

If you want it fixed, pull the jug and send it to an overhaul shop. I suspect that you can get the valves reground, guides replaced and a fresh hone for $500 or so. You can re-use the piston and new rings should be $50.

Larry
 
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I would lap it with a hose and clamp on the hose and pull on the hose as you lap. I’ve lapped that way with good results.
 
Thanks for all the reply's/reccomendations. As a first course of action I think I will attempt lapping it due to the fact it is the least invasive procedure and easiest on the pocket book. It is something I may be capable of doing myself without hiring it out and I can always proceed to the next course of action if not satisfied with the results of this one.

I have been attempting to educate myself not only on a fix for this but, what it is and what is causing it. After watching Mike Busch's video "why valves stick" I am convienced these are lead deposits created from running 100ll and running too low CHT'S. CHT'S run about 325*F in cruise. I have always leaned as much as I'm comfortable with both on the ground and in the air, but being carbureted and with steam gauges it may not be enough.
So now to figure out how to raise those CHT'S.

doug
2007 RV-9A
O-320-D1A
 
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