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10-02-2022, 07:22 PM
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Join Date: Apr 2013
Location: Ventura, CA
Posts: 393
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The Math
How does 1 part per 1000 = 1%?
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10-03-2022, 06:24 AM
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Join Date: Sep 2018
Location: LSZF
Posts: 1,160
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Quote:
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Dan: you had the stuck valve using mogas? i was under the impression that stuck valves are more a problem caused by leaded avgas.
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Yes, I've had. And I also had it on a C-90 engine using only MOGAS as well.
Back to this one... checking compressions this Spring, I found 1 cylinder showing 0, nix. One of the exhaust valve was found almost impossible to move, all ok once the guide was reamed. And this was at 330h into the 400h of the SB388C...
Paul, yes I've seen your thread. As someone else commented, I doubt it will be conclusive in any way. I've had stuck exhaust valves on different engines, C-90/O-320/O-360, flying AVGAS or MOGAS or mixed, at different typical power settings.
One factor which most of us, inclusive myself, miss, is the material those valve guides are made of, the answer might be there...
Last edited by Dan 57 : 10-03-2022 at 06:38 AM.
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10-03-2022, 06:40 AM
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Join Date: Feb 2005
Location: LSGY
Posts: 5,117
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Quote:
Originally Posted by Dan 57
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One factor which most of us, inclusive myself, miss, is the material those valve guides are made of, the answer might be there...
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Also, oil type, additives, and CHTs could be factors. |
10-03-2022, 07:59 AM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 6,453
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Mickey is probably closer to the mark. Given Dan's experience, it's unlikely that lead is the cause. More likely oil is frying onto the stem or guide or both.
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10-03-2022, 08:14 AM
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Join Date: Feb 2009
Location: Gilbert, SC
Posts: 359
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Read Mona’s STC instructions
My Mogas STC instructions for my old A65 powered Cub say to run one tank of leaded gas every 25 hours to add minimal lead to various parts of the engine. Any time running 100LL I add TCP.
Flying around the South East we don’t have much pump mogas at airports and no UL fuel yet.
Looking forward to 93UL or 100UL coming to airports across the country!
__________________
AL
<><
Launching from SC45
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10-03-2022, 08:55 AM
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Join Date: Sep 2018
Location: LSZF
Posts: 1,160
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Quote:
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and CHTs could be factors
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Yes, could be... the stuck valve cases I had were on different engines which I ran completely differently.
And if we take Marvel Oil, and other additives into account, and oil grade and the position of the stars, could be too...
I'm now heading towards the kitchen, luckily the machine's always plugged in  |
10-03-2022, 11:28 AM
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Join Date: Jul 2020
Location: Indianapolis
Posts: 209
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Why not use 2 cycle synthetic oil instead of Marvel Oil? It is made to be mixed with gas, lubricate everything in the engine and will not foul plugs. My airport golf cart runs well at 220 to 1...
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10-03-2022, 11:49 AM
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Join Date: Feb 2005
Location: LSGY
Posts: 5,117
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Amazingly on this month's "ask the A&Ps" podcast Mike Busch did recommend MMO for noisy lifters - perhaps it will help for stuck valves?
Last edited by rv8ch : 10-03-2022 at 12:00 PM.
Reason: Corrected recommendation from stuck valves to noisy lifters
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10-13-2022, 09:11 PM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 6,453
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In researching for another topic, I stumbled on to this document on the Conti website: http://continental.aero/xpublication...ives/si88-7-1/
Page 5 has some information on Mogas and valve seats. I'd question a couple of the statements made here but it still makes for interesting reading.
One does wonder if Lycoming and ECi seats are very different material though as the doom predicted here on a diet of Mogas doesn't seem to be taking out Lycoming seats. I think Pete Howell has over 2600 hours on his now...
Last edited by rv6ejguy : 10-13-2022 at 09:22 PM.
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10-14-2022, 11:21 AM
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Join Date: Jul 2006
Location: Payson, AZ
Posts: 124
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2 Cycle Oil Flashpoints
Quote:
Originally Posted by BoydBirchler
Why not use 2 cycle synthetic oil instead of Marvel Oil? It is made to be mixed with gas, lubricate everything in the engine and will not foul plugs. My airport golf cart runs well at 220 to 1...
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Typical 2 stroke engines do not have valves. The oil added to the fuel is for bottom end lubrication.
2 stroke oil flashpoints vary from less than 200F to over 500F. Most are below traditional aircraft engine CHT normal operating range.
I’ve seen many 2 stroke oils leave very gummy and sticky deposits on exhaust port variable timing mechanisms in modern 2 stroke motorcycle engines.
Perhaps adding 2 stroke oil as a top end lubricant in an aircraft engine will greatly increase the possibility of sticking valves.
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"The plane won't build itself..." RV-7A N7.62MM sold
-RV4 purchased. Extensive refurbishment complete. “Takes off by it’s self, flys hands off, lands by it’s self...”
-HRII project: paint and panel to go!
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