Stuck Valve

[jmbrwn]

Hey Guys- I've done some research and reading about this because my mechanic called last night and said during my annual he found a stuck exhaust valve on #1 cylinder. He performed the 'rope trick' and everything is put back together. I find it strange because I've experienced no engine roughness...actually my engine has run quite smoothly. I've noticed on initial run-up, my left mag would be a little rough...I attributed this to lead build up...after the flight , I'd do another mag check and it would check good. I've only owned the plane for about 6 months...engine has about 200 SMOH. I've used MMO and TCP religiously since ownership. Does anyone have any ideas on what would cause this? Am I operating the engine wrong somehow?

[GAHorn]

Stuck valves can occur during start-up (which is likely the condition your mechanic experienced, whether or not he was actually starting the engine.) Turbocharged engines (stay with me on this one... ) usually have as an operating recommendation ... instructions to allow the engine to idle below 1000 rpm for several minutes after landing in order to allow the oil pump to continue to scavenge (and supply) oil to the turbo-bearings. This is to prevent the bearings (hot from the recent flight) from "coking" the oil and siezing the bearings. When the engine is stopped the oil-flow stops...and any localized high-heat areas such as turbo bearings (and valve stems/guides) will cook the static oil. By allowing the engine to stabilize at low rpm, not only are the parts given time to pass their heat on to moving oil...but that hot oil is pumped on to join and pass off the heat with the rest of the oil in the sump.
I believe it's possible that similar action occurs with valve guides even in non-turbocharged engines.
Allowing the engine time to stabilize to a cool-down temperature before shut-down is a good idea. (The operating check list found in the Owner's Manual recommends a cool-down at 800 rpm for two to three minutes. The Continental Operator's Handbook also recommends an 800 rpm cool down "until cylinder temperature has been reduced appreciably...")

[jmbrwn]

Thanks for the reply, George. I'll try stabilizing my engine before shut-down...sounds reasonable. I read in an earlier search, someone recommended aggressive leaning...which I do...also while on descent and landing. I'll try this also. I usually, when I remember, go to full rich in descent and for landing double check full rich. It may have been that valve guide was a little tight even at overhaul and this would have happened no matter what? Hopefully I won't have any more stuck valves.

[GAHorn]

Well Jim, to tell the truth I've only experienced two stuck valves in TCM engines over 35+ years of flying, and those were someone else's airplanes. There are those present who have much more experience than I on this subject. But I believe there are two major causes of stuck valves.
Number one reason is coked oil in the valve guides causing insufficient clearance. The proper cool-down/shut-down of the engine should help in that.
Number two reason is lead and carbon buildup on the valve-stem. Aggressive leaning, TCP, MMO, are all indicated as corrective by most people. I have mixed feelings about MMO, but most people who use it swear by it. My mixed feelings are about it's lack-of-approval in aircraft...(no one in aviation manufacturing, no one at the FAA, and no one at MMO itself will approve it's use in aircraft)... and it's conflicted use as a fuel additive ....(if it's bad to have any jet-fuel/diesel in your gasoline---then how can a product that's basically just jet-fuel/kerosene with perfume and red dye be good? And if carbon can stick valves, doesn't burning light-oil in your fuel make more carbon?)... ...Versus: the pretty enthusiastic (even if anecdotal) endorsement by it's devoted users. Many years of MMO useage in various, historically-troublesome aircraft engines (like Jacobs radials) have produced a lot of owners who would no more take their airplanes flying without MMO than they would without motor oil in the sump. (A former mechanic at Delta Air Lines back in the 50's/60's personally told me the only reason Delta kept a better dispatch rate than chief-rival American was because Delta used MMO in it's aircraft.....until the Feds caught 'em at it, fined 'em, and made 'em stop putting it in the fuel,....and then Delta's stuck valve failures and flight cancellations became just as common as American's. The long-term fix was the switch to aircraft that could use 100% MMO for fuel....JETS!)
I"ve used it in cars, boats, lawn-mowers, generators, etc,., but never in my personal aircraft, and I've never had a stuck valve in any of them. (It's also a fantastic elephant-repellant. Elephants have never been seen in the Texas Hill Country.)

[Bruce Fenstermacher]

...(It's also a fantastic elephant-repellant. Elephants have never been seen in the Texas Hill Country.)

No Elephants in PA either. Guess it's all that MMo we're using.

[Jeff Palmer]

I had a friend who, for some reason, had several stuck valve problems. He did a precautionary landing, some place I don't remember, and the mechanic told him to use a product called Mix-I-Go. He never had a stuck valve since. I have been using it in my cars and it definately keeps the plugs, carburetor, valves and pistons clean. I have been using it in my airplane. My mechanic doesn't want me to clean my plugs when I take them out for my owner assisted annual. He always forgets and scolds me for cleaning my plugs before he sees them. But, I didn't clean them. I use Mix-I-Go. They also make something called MXO-AV for aircraft. But it's more expensive and doesn't work, for me, as well as Mix-I-Go. My valves and pistons are always are very clean. It's about $80.00 a gallon but that will treat 1200 gallons of fuel. Check it out... http://www.bfcd.net/mixigo.html

[N1478D]

I USE to have stuck valves, 4 or 5 times, same cylinder, same exhaust valve over a multi year period. First time on the ground after the first annual, the rest of the time up in the air, which I understand is not the average, been told they usually happen on the ground. At the first event was told to use MMO which I did. Stopped after a while and had the next occurence, started MMO again and still had more occurences. Never did anything to the valve, guide, etc but here's what I'm guessing stopped the stuck valves. After a few hundred hours it was time for the 500 hour Bendix mag deal. At the same time the mags were rebuilt, new plugs and harness's were installed. HOTTER SPARK!!! Have not used MMO for a few hundred hours, flown all over the place, Oshkosh, Petit Jean, etc. Burn both avgas and mogas. NO STUCK VALVES on an egine with over 1100 hours on it and the cylinders. Could be a coincedence and maybe I'll have a stuck valve this week. But, it looks like the new harnesses, plugs, and rebuilt mags did away with the stuck valve problem. MMO has not been in the equation for a long time now and although it gave me comfort to put it in when the old timers told me it would help, I don't have any way of knowing if it had any influence or not. The plugs were 400 to 500 hours old, the harnesses looked as if they were from the 50's, and the mags had a few problems the mag shop found. Each engine is different to some degree I'm sure, but in my case I think the problem was spark.

[dacker]

I use MMO on my door hinges, haven't had one stick yet!

[GAHorn]

Joe, just a guess...but I'd guess that your slightly tight valve guide (which may or may not have been properly reamed) has worn sufficiently that there's now sufficient clearance to avoid stuck valves in that position. I doubt mags/plugs had anything to do with it. (But your theory is better than the snake-oil ones I sometimes hear.)

[N1478D]

Well, that's certainly possible. One thing that seemed to be consistant was that the valve would stick on real humid days. Also, the frequency of the valve sticking was increasing up to the time the annual was done with the new harnesses, mag work, plugs, etc. After stating that the valve had not stuck for quiet some time I just knew it would bring me bad luck and the valve was going to stick the next time I flew her. And, this morning it was so humid the concrete was as wet as if it had rained, the clouds were at 1400 feet on my trip over Love Field and guess what - NO STUCK VALVE! George, if it was a too tight guide then maybe it has worn enough now, but that would not explain the increase in frequency. Another theory would be that something was lodging in the guide causing the valve to stick, but now with the hotter spark, that something is not there.

[johneeb]

Joe,

Hows this for a theory? Now that you have improved the ignition system on your engine perhaps the timing of the spark event is at the proper time and most of the combustion cycle is occuring while the Exhaust valve is closed as opposed to occuring slightly late and therefore lasting into the period when the Exhaust valve is open causing the Exhaust valve to run hotter and expand more and stick.

I have noticed this happening with the advent of no 80 octane fuel available, the exhaust gas temps have gone up and the efficiency of our O-300's have gone down slightly as the volume of fuel and air each intake charge has stayed the same but with 100LL a little more of it is going out the Exhaust pipe still burning due to the slower burning nature of higher octane (anti-noc) fuel.

Johneb

[N1478D]

That could very well be it Johneb!

Something with that cylinder (the one that has always had the stuck valve) has not been as it should be like the other 5 cylinders. So, some variable has been using that deficiency and promoting it to have problems. One of the variables is the fuel. Over about a 700 hour period, it did not seem to make a difference whether it was avgas or mogas. I have mentioned that it always happened when it was humid. The other thing is, although I fly low out of preference most of the time, I was either under a low ceiling, or I was desending thru an opening in the clouds when the valve would stick the great majority of incidents. Not sure what low altitude could possibly have as an element of the equation.

[blueldr]

What the hell id the big deal about a stuck valve? Out here in LaLa land , any time we get a stuck valve we install two new magnetos, new harnesses, AND a full set of new FINE WIRE spark plugs! Works every time and saves a couple of hours of labor!

[N1478D]

That's GREAT that there in la la land when you have 30 year old harnesses, 500 hours on your plugs, and it's time for the 500 hour AD on your mags, the reason you do all of that is because you had a stuck valve. Guess that's what makes it la la land.

On the other hand, it seems interesting that possiblities exist that it is not always the obvious that is causing the problem. But, some people don't like others to discuss those possibilities I guess.

[Metal Master]

Lycoming has a service bulletin on this issue for their engines. I have seen many stuck valves in Lycoming engines. And almost every case the cause was predictable. The pilot was flying along in cruise conditions and for whatever reason had to make a quick descent. (such as letting down through the overcast through a hole in the clouds) closed the throttle to make the descent. Then when he increased throttle the engine ran rough because of a stuck valve. My thoughts on this are that when you close the throttle manifold vacuum goes up which as the intake valve opens and can not get as much air from the intake path draws heavy oil and residue into the intake valve guide interface. The cylinder is cooling rapidly because of the descent and solidifies the oil & residue into the valve guide area. Result stuck valve.

Jim