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Checking for sticky valves and the MMO cure

A

aerial

Active Member
I have been doing some maintenance and tune-up on my Lycoming O-320-E3D.

Since I have the valve covers off I was wondering what is the best way to check for sticky valves, and if it was a good idea to pour some Marvel Mystery Oil into each of the cylinders at TDC and work the prop back and forth as preventative maintenance?
 
Hi David....

.....When valves stick, it is usually the exhaust since it's exposed to flame as the gases exit. The stem is what needs the lube and there are a couple of different ways to do that. I had a P+W 1340 cu. in radial and we used to suck it into the blower while the engine was running and it often freed up a sticky valve while it coughed and burped during the Marvel oil intake. Some also add a pint to full fuel tanks occasionally to prevent a stuck valve but unless you feel the engine running on three cylinders, don't bother.

Regards,
 
See latest issue of Sport Aviation

There is an article on oil in this issue which mentions MMO and in the context of sticky valves in Lyc's.
 
Thanks for the advice. I have read the Lycoming advice as well as what John has to say at Sacremento Sky Ranch, yet I know dozens of pilots who use Marvel in their aircraft.

It would be nice if there was an easy way to "get the lead out", as well as keep the valve guides nice and slick.
 
Has it occured to anyone,that if MMO were such a magical potion, wouldn't one of the oil companies incorporated it into their fuel?? Such a fuel would command a premium price as it would cure all sorts of engine problems....

In MHO, MMO is akin to snake oil and shouldn't be used to cure any engine problems.

The only way to clean up a valve guide and stem is to remove the valve and VERY LIGHTLY ream the guide and polish the stem. This can be accomplished without removing the cylinder from the engine. It takes a little 1/4"rope, a couple of hooks made of safety wire, an adustable reamer and a Maglight.
I believe that Lycoming has a wobble test, don't know the details but I belive thay have a service bulletin on it. If your guides are worn, the valves will continue to be sticky as the wearing allows the combustion products to work their way into the guide causing the valves to stick.
I wold not fly behind an engine with sticking valves, A sticking valve will cause a loss of power and if it sticks at the wrong time a bent push rod and perhaps a cracked push rod tube and loss of engine oil and an unplanned landing.
 
I have patients who swear rubbing MMO on their arthritic joints cures arthritis. I no longer argue with them because they are certain they are right.
 
The only good use I've found for MMO is the preservation of cylinders from rust. Other than that, just follow the service bulletins. Either ream it or find someone to.
 
MMO

Some tine ago, I helped a friend with a Pietenpol Aircamper powered by a Corvair. He called to find out if I had any idea as to why the engine (that has set for more than a year after a major OH and covered with MMO) would barely turn.
Looked down the plug hole and no apperrent sign of corrosion. The only solutuon was to remove the jugs. Pat decided to take the entire engine apart. Nothing was found, except that all moving parts appeared to move as if it was full of sand. I asked what he coated it with, he said MMO and STP.
Reassembled without the magic brew, and it ran well.
His partner Sam, did the same to his Corvair, and had the same problem turning it. Like Pat, Sam dissambled the entire engine. The pistons barely moved on their wrist pins. (Pins on Corvairs are shrunk fit) He didn't want to pressed then off. Knowing from Pat's engine that there were no signs of corrosion, I suggested that he "cook" them in hot thin oil (10W) they loosened. Sam reassembled and also ran well.
A third incident was with a C175 with an O300. The prop turned as if the engine was full of sand. After much prodding it finally released. Told the owner to runn it and see what happens. It ran fine.
He used MMO in the gas and in the oil as well. We suggested that he stops using it and switch to multigrade oil. So far as we know, it's still running.
Personally , I use the stuff, but not in engines.
FWIW
TT
RV10
 
MMO is for the most part a solvent. I don't know how much STP he used but perhaps the mixture was such he washed away any lube from the moving surfaces with the solvent effect of the MMO.

MMO is like medication. In the right amount, in the right circumstances it could give a desired result. Too much, in the wrong place, used in the wrong way could create an undesirable consequence. If you don't know what you are doing, don't self medicate.
 
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