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Stuck valves

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PTAirco

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I had my first stuck exhaust valve on an O-300 in my Maule M4. I've flown this quite a bit and most recently a couple of days ago. My friend borrowed it and flew it to Big Bear. Stayed overnight and flew it back in the morning. Barely got off the ground... Luckily it's all downhill to Flabob from there. He thought he was running on five cylinders. No, he was running on four. Two rear, left cylinders had no compression when I pulled the prop through after he landed.
Nothing unusual in one stuck valve but two!?!

We're doing the usual rope-trick fix. What I'd like to know is how to prevent it. People swear by Marvel Oil or TCP or even two-stroke oil. I have on occasion used MMO, based on the ton of anecdotal evidence out there but not on a regular basis.

The engine does not run hot generally , neither oil not CHTs. It was about 100 degrees here that day, but the seizure happened when it was pretty cool p there.
 

TFF

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Marvel in the oil and TCP in the fuel. Some put Marvel in the fuel too. Cold is normally when valves stick because of uneven expansion until operating temp. Gunk taking up the clearance. Lycoming added a little more clearance to the guide as a production fix. I don’t know if Continental did the same. I’m a fan of changing oil when it gets tired. When the oil starts burning more than normal like just before a change, it’s really time. There are commercial reasons to go all the way to 25 or 50 or whatever, but for a fun machine, fresh oil is better oil.
 

crusty old aviator

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Are you burning mogas or 100LL? Usually 100LL will lube the stems pretty good, provided they're nice & clean to begin with, but you have to run the engine at 1200 rpm and pull the mixture back very very very slowly to shut the engine down. This will momentarily superheat the inside of the cylinder, melting any balls of lead and blowing them out the exhaust, so they don't end up in your spark plugs.
After a tankful of 100LL, the stems & seats should be well coated with lead, and you can go back to mogas with MMO added to keep the top end lubed. There are so many variations of mogas, and none of them are formulated for these old engines...and don't even think about getting me started on the great ethanol scam.
I don't put MMO in the oil because most oils have enough stuff in them already.
 

Daleandee

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Marvel in the oil and TCP in the fuel. Some put Marvel in the fuel too.
Not sure what is allowed with your engine but on my experimental I use Decalin and MMO in the fuel. Sometimes I'll put a can of Seafoam in the tank (16 gallons). Some recommend Techron or Gumout but the key ingredient is P.E.A. (polyetheramine) which is said to be a very effective cleaner. But for certified engines this is verboten.

Someone else asked about the fuel you are using. I mix 100LL with non-ethanol auto fuel to just above 93 octane for my engine. This helps limit the amount of lead in the engine but it does seem to start easier and run better with a bit of 100LL in the tank.

FWIW ...
 

proppastie

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Lean of peak guys say you have to run lean of peak.
If I'mnot in the green on all the gauges (well warmed up)my values hang up and I have a rough running engine.
 

plncraze

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When I worked in a GA shop we had a O-235 come in with the same issue. Lyc. had a service bulletin to ream the guides.
 

TFF

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I know a student borrowing a friends 172 last week. Checks tanks for water. Red 100LL. He was like, what the heck! This guy doesn’t know about the old red fuel that these engines were supposed to be running on. An O-300 was not supposed to drink stuff with this much lead. Extended electrode plugs for fowling, TCP for fowling plugs, MMO sticking valves. All fixes for problems that were not designed for originally. It’s all a little voodoo and you can be the lucky person that never has a problem, and you can be the lucky one that always does. Pop the valves out, clean out the gunk, and start the clock again.
 

Pops

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Been using MMO in the fuel since the early 1970's and never had a valve stick. When 100 LL came out I started using about 50/50 with auto fuel. Owned 3 different 0-300 C-172's and a C-150, flying several thousand hours.
 

Orange4sky

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Go on Youtube and listen to Mike Busch on valve failures and leaning basics. His channel is Savvy Aviation, full of EAA seminars which are a gold mine of infomation on maintenance. Among other things he advises to lean aggressively everywhere except during runup, takeoff or steep climb. 100LL is terrible for promoting build up on the valve stems especially if you don't lean on the ground.

 

Victor Bravo

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For whatever it is worth, I stuck a valve on a Taylorcraft during a cross-country ferry flight, and spent a couple of days in a hot Texas town until the local IA did the "rope trick" and got me going again.

The only reason I was not us ing Marvel oil on that ferry flight is that the guy who I bought it from said "no, we never use that stuff around here..." and I thought I would not make any changes to the airplane until I got it back home.

I've never stuck a valve on any airplane that I was using Marvel oil in the fuel. So for whatever my opinion is worth I'm a staunch proponent of Marvel oil in the fuel.
 

PTAirco

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Are you burning mogas or 100LL? Usually 100LL will lube the stems pretty good, provided they're nice & clean to begin with, but you have to run the engine at 1200 rpm and pull the mixture back very very very slowly to shut the engine down. This will momentarily superheat the inside of the cylinder, melting any balls of lead and blowing them out the exhaust, so they don't end up in your spark plugs.
After a tankful of 100LL, the stems & seats should be well coated with lead, and you can go back to mogas with MMO added to keep the top end lubed. There are so many variations of mogas, and none of them are formulated for these old engines...and don't even think about getting me started on the great ethanol scam.
I don't put MMO in the oil because most oils have enough stuff in them already.

Most people who have expressed an opinion (informed or otherwise) on the matter think that 100LL is part of the cause; too much lead. I can't say I had much experience with this problem other than in an old Land Rover, so I am waiting to be elnlightened.
 

PTAirco

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Lean of peak guys say you have to run lean of peak.
If I'mnot in the green on all the gauges (well warmed up)my values hang up and I have a rough running engine.
I have a carb, so I lean the only way I can, but I do lean it a lot. All the time, especially on the ground.
 

PTAirco

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Go on Youtube and listen to Mike Busch on valve failures and leaning basics. His channel is Savvy Aviation, full of EAA seminars which are a gold mine of infomation on maintenance. Among other things he advises to lean aggressively everywhere except during runup, takeoff or steep climb. 100LL is terrible for promoting build up on the valve stems especially if you don't lean on the ground.

Yep, saw that. I like this guy.
 

PTAirco

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We did the rope trick and fixed the two stuck valves and I flew it this morning and all is fine. I'll do the remaining four as soon as possible. Used a Flex-Hone to clean out both guides. Even cleaned up, the valve seems tighter in its guide than I'm used to seeing on cars on motorcycles. Virtually zero rocking of the stem. There was a lot of junk in there.
I am going to use MMO for a while and see what happens. I heard of people using two-stroke oil too ( something like 100:1) - any opinions on that?
 

TFF

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100LL is a cover all fuel. It really is for high compression engines. Detonation for low compression is covered easy. The high compression chamber burn gets the lead hot and it goes out the pipe better. Low compression it can stick around. It gets past the rings and gets in the oil. MMO is essentially paint thinner in automatic trans fluid with stuff that smells to throw you off. It’s not about lubrication of the stems, it’s about contamination of the oil. MMO is keeping crud from sticking. When all the oil out there was mineral, it was much more popular. Modern ashless oil is way better but sometimes help is needed.
 

Dana

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MMO also, according to the MSDS, has some TCP. Whether it's enough to do any good is another matter.
 
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