Stuck- REALLY Stuck Valves - O-200

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Magman

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Magman
A bud has an O-200 with about 300 hrs and 6 years on new TCM cylinder assys.

It was running fine until he loaned it to someone.

The next attempt to fly revealed it had zero compression and 2 stuck Exhaust valves.

Even with cylinders removed they won’t budge.

Worst I’ve seen since the days of the “ Infamous X/C 2”.

It’s being majored now.

Thoughts on a cause?
 
Did the guy put mixed gas in it? Gas mixed with 2-stroke oil? Dumb, but you know how it is out there...the borrower might have figured that aircooled engines are all two-strokes and have to have mixed gas. Too many student pilots never touch a fuel nozzle or read a POH or anything else instructive to the care and feeding of an airplane.
 
Hopefully they didn’t put car gas with ethanol in. How many hours between last flight and stuck valves?
 
My understanding is that stuck exhaust valves are a common and infamous problem on the O-200 when operated with 100LL due to buildup of deposits. Could flying at a high altitude with mixture full rich do it on one flight?
 
Good points.

Not sure I understand “ how many hours”

He flew it about 2 hours and was up to 5000 feet and next time he went to

fly they were STUCK..

No flights in between.

It was filled with 100 LL that was available so no incentive to use other

fuel. He is planning on dumping fuel just in case something like Dan or Frfly

happened. A BIG concern is that the same fuel in tanks not be used

after O/H.


Issues I’ve seen often gave a warning via “Morning Sickness”.

Engine guy says recent HOT event.

Full power and LEAN would likely show detonation signs as well.
 
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Was flying a 150M at a flight school a few years ago. Started fine, taxied fine. Nice, smooth idle, no morning sickness. Got to the run-up area, reved up the engine, a few seconds later, before I even had a chance to cycle the mags, the engine starts missing and shaking badly. Nothing we tried worked. Taxi back to the hangar, hoping for fouled plugs, but the're clean. Come to find out two cylinders had stuck valves, with no warning signs whatsoever.
 
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Not a O-200 but a C-85 in the Ercoupe I used to own. Very similar situation. Flew one week, all fine. Went on a long cross country trip with no issues. A week later, no signs of issues until a few hundred feet off the ground. Couldn't make full rpm, climbed at 100 ft/m. Managed to land on the cross runway, taxi back, thought fouled plugs, or mag issues, but found out had a stuck valve, which ultimately caused more damage to the lifters and whatnot. So, we ended up pulling the engine for an overhaul. Three months later, the plane was back in the air with no issues until I sold it. These small engines on 100LL tend to do that, or so I was told by my mechanic back then.
 
An engine overhauler told me that Continental's minimum clearance for those valves was too tight, and they'd stick.
 
Thanks for the replies.

Owner is checking Flightaware for flight profile and track.

If mixture was leaned at at altitude followed by a landing the engine

would likely lose power. If a couple touch and goes with full power

and leaned could heat things up.

Dan; any idea of how long TCM has the tight clearance?

We believe the engine was running fine until shut down.

Then the valves seized to the guides.

Pushrods appear to be not bent which would support this thought.

Right now there is some hope cylinders will be able to be reworked.
 
Magman said:
We believe the engine was running fine until shut down.

Then the valves seized to the guides.
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I had that happen while learning to fly. It was in an O-300, the big brother to the O-200. Same cylinders. Couldn't fly the airplane home, so the instructor and I took a Cessna Cardinal. First and last time I flew one. It was one of the 1968 150-HP models, underpowered. But a really nice airplane. Only about six years old.
 
Magman said:
Dan; any idea of how long TCM has the tight clearance?
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I don't know. This is from a 2011 version of the overhaul manual:

1725806575822.png

So for the exhaust valves, .003 to .0045". I don't have an older manual for comparison
 
Since these cylinders were purchased from TCM it would seem they would

be in spec per that Chart. What does your contact recommend?

We may have input when jugs are being worked on.

I’ve also heard too loose allows carbon buildup and sticking.


Some folks on another forum said they had the issue when using

Camguard. It was used in this case.


I have about 50 hrs in Cardinals and share Dan’s opinion. My preference
.
would be a C-177A which would be 180hp, fixed pitch and no D-mag.

Not too common. IMHO Cessna made the right choice in dropping the

Cardinal and keeping Skyhawk.
 
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Magman said:
What does your contact recommend?
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He reamed the guides to a larger clearance than the minimum.

The aluminum head and bronze guide will both expand at twice the rate per degree that the steel valve stem does. That means that the clearances should get larger when hot, though that valve stem is going to be somewhat hotter than the guide, so the clearances will get at least somewhat larger. Exhaust deposits get into the clearance, and if things are hot enough, they bake on that stem and guide, and when the engine cools down, they're in there and now they jam everything tight.

Too much clearance invites more buildup. Too little makes it easy for a little buildup to jam things. I don't know where the sweet spot might be.

100LL has four time the lead that the engine was designed for. It's a problem. Maybe Camguard is a problem, too.
 
That does make sense.

And as the clearance increases less heat is conducted from the Stem.

I doubt if it can be determined what the clearance WAS in this case.

Why 2 at the same time? Who knows?

When 100 LL initially replaced 80/87 it was the Intake Valves that were the

problem.

Mo-Gas = alleviate?
 
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Dan Thomas said:
I don't know. This is from a 2011 version of the overhaul manual:

View attachment 133252

So for the exhaust valves, .003 to .0045". I don't have an older manual for comparison
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Replying to my earlier post; I was going through boxes of my books and came across the same manual, but from 1973. It has the same stem/guide tolerances as shown above. Note that the O-200's valves are tighter than the C75/85/90's; I suppose one could use the numbers for the older engines as long as you're within the .008" service limit. I would shoot for the max O-200 limit of .0045".
 
What has puzzled me is that some aircraft seem more afflicted than

others even though they have the same cylinders and operating conditions.

At one time my belief was this was due to carburetion operating

techniques. Now I’m not so sure. My guess is less valve issues with

mo-gas than 100LL. IIRC there were few problems with 80/87.

Some of these engines may have been nursed on 73 octane juice.
 
Magman said:
What has puzzled me is that some aircraft seem more afflicted than

others even though they have the same cylinders and operating conditions.

At one time my belief was this was due to carburetion operating

techniques. Now I’m not so sure. My guess is less valve issues with

mo-gas than 100LL. IIRC there were few problems with 80/87.

Some of these engines may have been nursed on 73 octane juice.
Click to expand...

I can tell you of two cases where small Continentals were run exclusively on mogas for hundreds of hours and stuck one or more valves on startup after an hour or two of running 100LL followed by an overnight stay while traveling. In those cases my suspicion has been that the extended use of mogas caused the valve to guide clearance to open up enough that when lead was reintroduced it filled the gap. Those valves were all stuck bad enough that I had to remove the cylinders and beat or press them out.

Baffling/cooling also seems to influence the probability of problems. I'm not convinced that mixture/carburetion is a main source of trouble because if it was, a couple of people I know would have chronic valve and cylinder problems with the way they run their engines. While not nonexistent, their problems seem to be minimal.
 
mondtster said:
I can tell you of two cases where small Continentals were run exclusively on mogas for hundreds of hours and stuck one or more valves on startup after an hour or two of running 100LL followed by an overnight stay while traveling. In those cases my suspicion has been that the extended use of mogas caused the valve to guide clearance to open up enough that when lead was reintroduced it filled the gap. Those valves were all stuck bad enough that I had to remove the cylinders and beat or press them out.

Baffling/cooling also seems to influence the probability of problems. I'm not convinced that mixture/carburetion is a main source of trouble because if it was, a couple of people I know would have chronic valve and cylinder problems with the way they run their engines. While not nonexistent, their problems seem to be minimal.
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I've had this happen on my O300 at least twice now. I run mogas pretty exclusively and have had 2 very stuck exhaust valves in the last 5 years while burning 100LL on x-country flights. I do run lean, as lean as I can with no engine monitor (now bought awaiting install).
There's a guy over on the old Cessna 172 forum (now Pilot's Place forum) that is blaming Camguard. First I've heard of that.
I'm looking forward to seeing what the engine monitor says.
I'm contemplating valve guide reaming at 200 hour intervals.
 
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