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  #1  
Old 03-31-2021, 03:16 PM
Larry DeCamp's Avatar
Larry DeCamp Larry DeCamp is offline
 
Join Date: Apr 2010
Location: Clinton, Indiana
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Default Sticky valve question for gurus ?

Today I reamed a sticking valve on Mellinium cylinder with 250 HRs. There was only carbon in the reamer and the valve stem had some bronze scuffing. The valve and cylinder look perfect with a scope.

I only use no alcohol mogas and lean ROP. Oil is XC 20-50 and camguard. Plug insulators are white and Pmag checks on ground and air are no differenc.

So, what is the carbon source, CAM GUARD ???
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  #2  
Old 03-31-2021, 03:39 PM
Mike S's Avatar
Mike S Mike S is online now
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Quote:
Originally Posted by Larry DeCamp View Post
Today I reamed a sticking valve

I only use no alcohol mogas
The lead that you are not getting in your mogas is among other things, a lubricant for the valves.

https://www.mcall.com/news/mc-xpm-19...975-story.html
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  #3  
Old 03-31-2021, 03:48 PM
BobTurner BobTurner is offline
 
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How far ROP do you run? If LOP there should in principle be no carbon, it would all be CO2.
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  #4  
Old 03-31-2021, 03:55 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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You must aggressively lean when on the ground - as in just before cutout.

I run LOP 95% of the time and strive to keep CHTs in the 350-400 degree ranged as stuck valve preventative measures. I refer your to Mike Buschís Webinar on stuck valves: https://youtu.be/7ohsVvYbAaQ

Carl
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  #5  
Old 03-31-2021, 05:03 PM
erich weaver's Avatar
erich weaver erich weaver is offline
 
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Location: santa barbara, CA
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Quote:
Originally Posted by Mike S View Post
The lead that you are not getting in your mogas is among other things, a lubricant for the valves.

https://www.mcall.com/news/mc-xpm-19...975-story.html
Hey Mike
Iím not getting anything relevant from that link. It is my understanding that the sole purpose of lead in leaded gas is as an anti-knock agent and that the valve lubrication thing is a myth. Curious to know more if possible.

Erich
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  #6  
Old 03-31-2021, 05:13 PM
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Mike S Mike S is online now
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From above link;

The relatively new, mid-octane unleaded fuel now becoming available matches the 89-octane rating of leaded fuel. But it lacks the equally important lubricating qualities of leaded fuel.

"Lead acts as a solid lubricant," said Jim W. Garthe, a fuels specialist in the agricultural engineering department at Penn State University. "When lead burns in the engine it forms white deposits . . . (with properties) sort of a like a graphite."

This was something I have heard for many years, the link was just something I found with a quickie Google search.
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Flying as of 12/4/2010

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  #7  
Old 03-31-2021, 05:24 PM
BillL BillL is offline
 
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Location: Central IL
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Quote:
Originally Posted by erich weaver View Post
Hey Mike
Iím not getting anything relevant from that link. It is my understanding that the sole purpose of lead in leaded gas is as an anti-knock agent and that the valve lubrication thing is a myth. Curious to know more if possible.

Erich
Yes, octane boost is the primary purpose, but the dry lubrication is a side effect. The valve faces and seats were once softer and when lead was removed from auto fuel, the valves had reduced life due to face wear. Valves never seat around the full circumference of the seats/valves resulting in some movement to align them when seating. For longer life and lower cost availability of materials, and vendors aviation engine manufacturers migrated to the same benefit. So, since this took place 60 yrs ago, it may be legitimate to call it a myth.

Someone asked where the carbon comes from. When fuel or oil cook hot and slow, both will deposit carbon. For exhaust, it is likely just the oil. Although . . during starting everything is cold and A/F is rich, fuel could get deposited then. Also, oil leaks past rings when sitting and could add a film to the exhaust stem from the hot end each start.
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  #8  
Old 03-31-2021, 06:39 PM
z987k z987k is offline
 
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Location: Alaska
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Quote:
Originally Posted by Carl Froehlich View Post
You must aggressively lean when on the ground - as in just before cutout.

I run LOP 95% of the time and strive to keep CHTs in the 350-400 degree ranged as stuck valve preventative measures. I refer your to Mike Buschís Webinar on stuck valves: https://youtu.be/7ohsVvYbAaQ

Carl
I'll second this video.
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  #9  
Old 03-31-2021, 07:31 PM
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rocketbob rocketbob is offline
 
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IMO the only thing that causes stuck valves is dirty oil. I do not change oil based on hours or calendar time. Gets dark brown, almost black...change it. My last oil change in my Comanche was at 44 hours.
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  #10  
Old 04-01-2021, 06:44 AM
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Walt Walt is offline
 
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Location: Dallas/Ft Worth, TX
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Quote:
Originally Posted by Larry DeCamp View Post
Today I reamed a sticking valve on Mellinium cylinder with 250 HRs. There was only carbon in the reamer and the valve stem had some bronze scuffing. The valve and cylinder look perfect with a scope.

I only use no alcohol mogas and lean ROP. Oil is XC 20-50 and camguard. Plug insulators are white and Pmag checks on ground and air are no differenc.

So, what is the carbon source, CAM GUARD ???
I suspect the engine oil is the source of the carbon, what CHT's you run? (I suspect they are on the high side)
I probably have seen more stuck valves in superior cyl's than others.

I think sometimes it the luck of the draw, if you get cylinders with tight stem/guide clearances you are much more likely to get a stuck valve.

I change oil every 25 hrs and lean aggressively, I have really good CHT's (generally 300-350) so tend to run very close to peak EGT/max power on the rich side (65-75%). Never had a stuck valve (I know never say never). Always had ECI and now Titan cyl's.

If you're having to clean lead out of the bottom plugs every time you pull them that's not a good sign.
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Last edited by Walt : 04-01-2021 at 06:54 AM.
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