Recommend NorCal person to lap valve

[- Poindexter -]

Wanted to see if anyone can recommend someone that can lap a valve and/or also ream? NorCal is the preferred area (plane is based at Gnoss, KDVO).
ECI O-360 engine, 950 hours. Compression test in the low 50’s. Lee Ataka (Rio Vista) is too busy, unfortunately. Any recommendation would be great.
Photo of valve below.

 

[lr172]

If that 50/80 leak is due mostly to the exhaust valve, it may have warpage and therefore not likely addressed by lapping. Have you borescoped that area? Do you see imperfections on the seat or valve that may be preventing it from fully closing? If the surfaces are clean, there is a good chance it has already warped. Lapping is good for debris on the surface, but typically can’t address any significant amount of warping.

Good luck with your efforts. Lapping is still worth the effort, as the alternative is far more costly. Just setting expectations.

 

[Dan 57]

on top of @lr172 comments, I'd like to add that that photo clearly shows a discolored overheated area (8'oclock), meaning the valve doesn't rotate anymore. Maybe salvageable, maybe not.
The procedure I'd apply would be to:
- remove valve cover
- have a look as to everything is looking (debris, broken springs, signs of overheating, etc)
- remove the rocker arm pin and the rocker arm
- remove the keepers and springs on the offending valve
- rotate the free valve by hand, not only pulled out as in closed, but also when pushed in. The valve should move freely by hand, with a silky feel
- if the valve is stuck or doesn't move freely, then the guide and the valve stem needs cleaning, lead and coke removal
- if the valve moves freely, the lapping could, again could, resurrect the lo compression
- if either procedure works, reinstall the springs/rocker arm/etc using a new rotator cap

 

[lr172]

on top of @lr172 comments, I'd like to add that that photo clearly shows a discolored overheated area (8'oclock), meaning the valve doesn't rotate anymore. Maybe salvageable, maybe not.
The procedure I'd apply would be to:
- remove valve cover
- have a look as to everything is looking (debris, broken springs, signs of overheating, etc)
- remove the rocker arm pin and the rocker arm
- remove the keepers and springs on the offending valve
- rotate the free valve by hand, not only pulled out as in closed, but also when pushed in. The valve should move freely by hand, with a silky feel
- if the valve is stuck or doesn't move freely, then the guide and the valve stem needs cleaning, lead and coke removal
- if the valve moves freely, the lapping could, again could, resurrect the lo compression
- if either procedure works, reinstall the springs/rocker arm/etc using a new rotator cap

IMO, the hot spot shows an area where the valve is not making contact with the seat. Whenever there is no contact, the valve can't shed its heat and therefore shows the signature of excessive heat and we get something like your pic. If the issue preventing the contact is on the valve, then the hot spot will stay in the same place on the valve even if the valve is rotating correctly. When the issue preventing contact is on the valve seat and the valve is rotating correctly, I would expect the burn pattern to be evenly spread across the valve (classic burnt pizza image). In the same way, if the valve is not rotating and the issue is on the seat, then we also get a burn pattern similar to what you see in your pic.

I would say that a hotspot like in your picture First and foremost, tells us there's a lack of contact. It is also possible the valve is not rotating, but the lack of rotation is not, in and of itself, the cause of the hotspot and fixing the rotation issue will not address the root cause of the overheating.

Dan brings up good points and you would be wise to follow his guidance and check all those items while you're in there. However, burn patterns typically mean there is at least a thou or two of clearance and lapping won't address that. If the cause of the excessive clearance is some type of debris stuck to the face, then lapping can effectively remove it. If the cause is warpping or some other wear issue, including a worn guide, then a valve job is typically required.

 

[- Poindexter -]

Larry & Dan,
Thanks for your excellent feedback, and some initial exploration has been done. While I can change mags and fuel pumps, I prefer “adult supervision” for moving forward with this valve. Per my message, looking to see if there is a recommendation for a person or shop in Northern California.
Thanks,
Paul

 

[FlyDave]

Paul,

Have you tried Scanlon Aviation there on the field?
Also, Bill Sherlock in hangar 611 there at Gnoss.
Also, @rolf here on VAF is at Petaluma may be able to help out.

Dave

 

[- Poindexter -]

Follow-up to get closure, which may help someone else out.
Larry was correct in that there WAS warpage in the exhaust valve, so we replaced it with a new one. We didn't even bother with lapping.

Thanks Dan for the encouragement in self-doing this work (with A&P supervision). It was pretty easy and straightforward.
This video was pretty accurate for my 0-360 (except this is a piston video, not valve specific).

And, for Dave, Rolf became available, so we were able to get this done in short order. Here is a photo of the removed exhaust valve. For reference, the compression test last year (and previous year) was in the 60's, and this year it was in the high 40's to low 50's. The borescope this year (over last year) definitely showed the creep of the burned area.

 

[erich weaver]

Larry was correct in that there WAS warpage in the exhaust valve, so we replaced it with a new one. We didn't even bother with lapping.

How is valve warping identified?
Thanks

 

[lr172]

How is valve warping identified?
Thanks

With the cylinder in place, just shine a flashlight into the exhaust port. If you see light coming through between the valve and the seat in some areas, but not all, it's warped.

 

[Raymo]

With the cylinder in place, just shine a flashlight into the exhaust port. If you see light coming through between the valve and the seat in some areas, but not all, it's warped.

Follow-up to get closure, which may help someone else out.
Larry was correct in that there WAS warpage in the exhaust valve, so we replaced it with a new one. We didn't even bother with lapping.

Thanks Dan for the encouragement in self-doing this work (with A&P supervision). It was pretty easy and straightforward.
This video was pretty accurate for my 0-360 (except this is a piston video, not valve specific).

And, for Dave, Rolf became available, so we were able to get this done in short order. Here is a photo of the removed exhaust valve. For reference, the compression test last year (and previous year) was in the 60's, and this year it was in the high 40's to low 50's. The borescope this year (over last year) definitely showed the creep of the burned area.
View attachment 92597

I've seen some like yours that were saved with lapping but I also have a valve like yours sitting in my hangar that I decided was too far gone and opted to install a OH'd spare that was sitting in the corner.