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bjb3013

Well Known Member
I have a Lyc IO360-A1A, cylinders 25 Hrs since OH.
Thursday AM I took off for SNF. About 30 seconds into the flight I noticed a slight surging. It smoothed out so I circled the airport and found that #4 egt was really low. Surging continued getting worse. I landed and swapped plugs . Now running on the ground with 3 cylinders and shooting fire out of the exhaust . Pulled the plugs and looked in the holes with a flash light. Now I really get the **** scared out of me. I see a 1/2 circle imprint of the intake valve on the piston top ???

Pulled cylinder today. Seems the intake valve seat came totally out of the head and is wedged under the valve. What causes this? The piston is bashed up, but the only thing I see wrong with the cylinder is the seat and the bent valve. Can't see any cracks. How should the cylinders be checked during OH to prevent this ? Is it possible to fix this? Now I am wondering about the other 3.

BB
 
Not put in right

The only way that wuld happen is if there was not enough of an interference fit between the seat and the head.

They should be heat shrunk in there....I.e seats are physically bigger than the hole, the head heated, seat chilled and the two are mated.

I've never heard of this happening, then again I have not been around airplane mototrs that long.

Well I would say Lyc owes you a set of 4 cylinders and then you need to ask what the likely hood of the rod bearings being trashed as well?

They maybe fine but you need to get Lyc's take on this to start.

What a bummer!

Frank
 
Weird but interesting

If there was no metal its just a jug and piston change. That is pretty cool. Not sure if there is anything to do with the rod big end? I'd call them for sure.

Try changing one rotor on a mazda or cylinder on a subaru while its still mounted on the plane. It also got you back on the ground. Aces. Sorry for you troubles. Never heard of this problem or what would cause the seat to become dislodge. Its pressed in to beat the band.

It just goes to show a Lyc can take a beating and keep on ticking.

Where they used OH cylinders or new? Who did the cylinder overhaul or what brand of new was it?

Glad you, your plane and most of your engine is OK :D
 
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Yea I was thinkin the same thing. What does ECI have to do with it? This kind of problem comes from high CHT. Usually, Sometimes.
 
Overhauled...

Rivethead said:
Yea I was thinkin the same thing. What does ECI have to do with it? This kind of problem comes from high CHT. Usually, Sometimes.
Click to expand...

Yes... and if they were poorly overhauled, it could have been the previous lifetime's high CHTs... :(

If it was a Lycoming factory overhaul (their terminology) - then it had new cylinders put on it.

Who did the OH?

gil in Tucson
 
<<Seems the intake valve seat came totally out of the head and is wedged under the valve. What causes this?>>

In general, incorrect interference fit. The minimum is around 0.0065", max around 0.010", meaning the OD of the valve seat ring should be 0.0065" to 0.010" larger than the machined hole in the head casting.

<<The piston is bashed up, but the only thing I see wrong with the cylinder is the seat and the bent valve.>>

I'm a conservative, but a bashed piston would push me to a full teardown for a magnaflux check of rod, pin, crank and crank gear.

<<Can't see any cracks. How should the cylinders be checked during OH to prevent this ?>>

You would need to remove the valve seats; no other way to check an installed interference fit.

Since yours has uninstalled itself, you have the opportunity for a little forensic measuring. These are 25hr cylinders? My long-distance guess is that your cylinder had a seat replacement during overhaul. Seats come .010", .020", and .030" oversize. The overhauler removes the old seat, does a clean-up cut in the head recess with the proper oversize cutter, and installs a new matching oversize seat. If, for example, somebody with a hangover cuts the recess with a .020 cutter and installs a .010 seat, it would probably stick enough to get through the subsequent seal face cut and assembly.

Soooo, measure your seat bore ID and the seat OD. If they don't match the dimensions in the Lyc manual, I'd be having a chat with the factory.
 
I agree

There is no way this is any kind of acceptable...I would leaning towards the complete engine strip as well...Remember the seat got squished between the piston and head...This (large) metal crunching load got transferred all the way to the crankshaft.

This need to be paid for by whoever provided those cylinders.

Frank
 
Tear it right down and magniflux crank and rods. Any time you wail a piston metal to metal better to be safe. Weird, someone didn't use their mic that day, couldn't of had correct interference fit.

Used to see this once in a while on Corvair 140 engines when seriously overheated from a tossed fan belt. CHTs would go over 500F and then bad noises would start happening. Always intake seats which run colder and don't expand as much. Improved staking around seats fixed this.

BTW- liquid cooled engines don't drop seats since the seat is always way hotter than the head casting. This assumes that a complete idiot didn't install them of course.
 
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Actually I have seen this several times on automotive engines in the last 25 years I've been working on them. count yourself lucky it happened in the pattern.
 
bjb3013 said:
Pulled cylinder today. Seems the intake valve seat came totally out of the head and is wedged under the valve. What causes this? The piston is bashed up, but the only thing I see wrong with the cylinder is the seat and the bent valve. Can't see any cracks. How should the cylinders be checked during OH to prevent this ? Is it possible to fix this? Now I am wondering about the other 3.
BB
Click to expand...

It sure speaks volumes for tossing out cylinders and replacing them with new ones at a major. I understand Lycoming won't re-use the cylinders so the overhaul obviously wasn't done by them.

Bob Barrow
 
Captain Avgas said:
It sure speaks volumes for tossing out cylinders and replacing them with new ones at a major. I understand Lycoming won't re-use the cylinders so the overhaul obviously wasn't done by them.

Bob Barrow
Click to expand...

The term "overhaul" is very subjective in the Lycoming world.

With my last 0360 the overhaul guys said I could use the original cylinders as they were in service limits, but we opted for new Milleniums. The old cylinders were in turn sold to a different overhaul shop and for sure ended up in some other engine being "overhaul".

Unless the overhaul is to new limits, the engine will have many used parts meeting service limits, these parts could have thousands of hours. It is buyer beware for sure.
 
The term "overhaul" is very subjective in the Lycoming world.

...the engine will have many used parts meeting service limits, these parts could have thousands of hours. It is buyer beware for sure.

Not sure what your point is here, but if your point is that you converted guys will never be troubled by deciding whether to re-use parts with thousands of aircraft hours on them, you are probably correct.....there are no such high hour parts to think about.

In the automotive world the term overhaul is just as subjective, and in general, folks need to clarify what they are buying.

I am frankly amazed at how tough the engine was here...have seen a number of dropped seats/valves in other engines and it ususally ended up with a seizure.
 
Jconard said:
The term "overhaul" is very subjective in the Lycoming world.

...the engine will have many used parts meeting service limits, these parts could have thousands of hours. It is buyer beware for sure.

Not sure what your point is here, but if your point is that you converted guys will never be troubled by deciding whether to re-use parts with thousands of aircraft hours on them, you are probably correct.....there are no such high hour parts to think about.
Click to expand...

Wasn't trying to make a point re conversions...just stating a fact re overhauls. The difference between a field overhaul and a factory overhaul is substantial - some guys new to this world don't really understand what that means. Zero time since major means nothing without a lot of paper explaining what was done. It remains buyer beware for sure.

(By the way, I am no convert, whatever THAT means....simply trying something different and finding it rather interesting. Two previous airplanes were Lycoming and worked out just fine. It's a great engine, warts and all. :)
 
I've never seen a dropped valve which didn't cause major engine damage but seen some dropped seats which have caused minor damage to the head and piston maybe. Very different failures.
 
You definitely want to magnaflux any parts which received stress from the event. Many years ago, the fiat X1/9 I had suffered when the teeth on the timing belt sheared and the piston and valve were inappropriately introduced to each other. The valve bent and the piston beat on it for a short time. I tore down the engine, had the head overhauled, purchase a new piston and an overhaul kit. After everything was reassembled, I ran the engine and all seemed well until about 3 days later when there was a loud bang and I quickly stopped the engine. Raising the lid, I looked at the engine and was quickly shocked when I noticed I could see the crank from the outside :eek: . The rod which was reused broke in half and swung around, knocking a baseball sized hole in the casing.

Don't assume that because all looks well that the part is still usable. I was 19 at the time, but still should have known better. Fortunately, in this case I could open the door and step outside!!
 
I had the head break off of an exhaust valve in a C-145 (6-cyl) in my 170 about 2 years ago. I was cruising at 7500 ft, heard a bang, then engine roughness like a valve had stuck. Full throttle still got me 2000 RPM. I was able to land safely on an unattended airport about 12 miles from the original incident. Multiple holes in the piston, but it stayed together. The valve head was jammed sideways in the seat. The next day we drained and flushed the case, installed a spare cylinder and flew the airplane home. (I now have a different engine on the airplane.)

This was my "spare" engine and I had been running it about 175 hours. I knew it was high time but it had been running well up until the incident. The engine had been "overhauled" back in the '60's but closer perusal of the logbooks revealed that the overhaul consisted only of new bearings and pistons. Per the logbook, the top end of the engine, other than the pistons, had over 3300 hours on it.

I guess the moral of the story is that unless you buy an engine brand new, take a VERY close look at the logs and get a good idea of what you've got.

Miles
 
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In addition to the magnaflux and such, I'd be concerned about the same thing happening on another valve seat. You definitely have to figure out why that thing popped loose.
 
rv6ejguy said:
I've never seen a dropped valve which didn't cause major engine damage but seen some dropped seats which have caused minor damage to the head and piston maybe. Very different failures.
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OK, well here is my dropped valve story that didn't cause major engine damage. Now I know it is not airplane engine related but none the less it is an incident that I think is relevant. I was 19 like Trib and as much as I thought I knew everything there was that needed knowing, I was like all other teenagers, very ignorant about what I was about to do.

I owned a candy apple red 1965 Mustang 2+2 fastback with 289 and 4 speed tranny. A real hot rod and dangerous in the hands of a 19 yo full of testosterone. Driving home late one night I was about 30 miles from home cruising down a deserted two lane highway at about midnight. I was booking it out on that deserted highway about 70 mph when all of a sudden the whole car started lurching and the engine started running very very rough. I had one of those after market under dash triple gauges that had water temp, oil pressure, and amps. I looked at the oil pressure gauge just in time to see it go from its normal 40 psi to 0.

I quickly pulled the car over to the side of the road and came to a stop. The engine never did die and as I backed the rpm's down to idle the oil pressure came back up to about 25-30. The engine was still running although it was definitely not running normally. The car was running but I could tell it was missing quite badly. Since I was out in the middle of nowhere and 30 miles from home late at night I decided to chance driving on. So I took off again headed for home. The engine continued to run but very roughly. As an ignorant 19 yo I ran that thing 60-65 mph the entire 30 miles home. I parked in the driveway, walked in the house and went to bed.

A day or two later when I was able to work on the car I pulled the valve covers off to examine what was going on. It was then I discovered that the valve spring keeper on one of the exhaust valves had broken. This allowed that valve to drop down onto the piston. So hear is the part that amazes me still to this day. I should have never been able to start that car up when I pulled it over to the side of the road. That valve should have been destroyed and in the process destroyed a whole bunch of other things necessary for that engine to run. But it didn't.

The valve had dropped down onto the dome of the piston. The piston then shot it back up into the head where somehow miraculously the valve stem bent just enough to then catch on the spring, the lip of the guide or something. At any rate it had caught just far enough up to hold it up off of that piston as it churned away at 2000 rpm or so for another 30 minutes. The only damage other than the valve itself and the keeper was a crescent shaped gouge in the top of the piston where that valve hit when it dropped.

I took the head in to a machine shop. I had the guide honed, put in a new valve, spring, rocker arm and keeper. I bolted the head back on the engine and drove it another 5 years without one problem related to the valve dropping incident what so ever.

So I can attest first hand to the fact that you can drop a valve and not have it cause major damage. Now I might add that I would not want to ever experience that again. Especially in an airplane that I cannot just pull over to the side of the road with. That incident scared the begezzus out of me just driving down the road. If it were to happen to me in the air . . . :eek: ~~~ well lets just say I would not wish that upon anyone.

Live Long and Prosper!
 
That is a pretty good story!

The term dropped valve usually refers to the valve head separating from the stem and floating around in the chamber until it turns sideways and goes through the piston.

Seen lots of bent valves, broken keepers/ springs etc. on auto engines where the engine has runs for weeks afterwards.
 
BB,
Ok, tell us the rest of the story. Exactly what sort of cylinder was it? Brand new, or overhauled? Where did you get it? Have you measured the seat OD and head recess yet?
 
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