Exhaust Valve Came From Together

Fearless Tower

Fearless Tower

Touchdown! Greaser!
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Fearless Tower
Lost an exhaust valve on the Twin Beech. Well, didn’t exactly lose it. The whole valve broke off the stem and wedged itself sideways in the exhaust port.

Photo is kind of crappy, but it wedged itself in such a way that the stem was able to go up and down next to the valve. What you see in the photo is the face of the valve next to the valve stem.

Curious why it failed the way it did though. The valve face doesn’t look burned or cracked like other failed valves I’ve read about. Any thoughts?

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Assuming no defect in the stem there was some sort of alignment problem that fatigued the stem.
 
heat is usually the stressor....I bet it was leaking and wasn't cooling....and that accelerated the fatigue mechanism.
 
Checkout_my_Six said:
heat is usually the stressor....I bet it was leaking and wasn't cooling....and that accelerated the fatigue mechanism.
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If that was the case though (valve was leaking) wouldn’t we have seen low compression on that cylinder at annual ~15 hours ago?
 
Stuff like this kinda makes we wish I had a pair of 9 cylinder JPIs...
 
Fearless Tower said:
No. Less than 500 SMOH. Single probe Alcor EGT gauge.

I can attest to the bulletproofness of P&Ws.....when it happened, the engine kept on trucking just fine, albeit a bit rough.
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was that a brand new valve?....or did it nicked (get a grove cut in it) when it was resurfaced?
 
Some valves have heads that are welded to the stems. I don't know if the R985 has them or not but could the head have simply came off? As alluded to previously, if the valves were reused at overhaul you may have no idea how many hours are on them.

Also, there could have been something else that happened first, causing the head to break off. Did a valve spring break or did the keepers come out? I'm not familiar enough with the R985 to know, but if the valve stuck would the piston hit it?

Working in an engine test lab, we see these failures from time to time. It's not an uncommon occurrence.
 
mondtster said:
I'm not familiar enough with the R985 to know, but if the valve stuck would the piston hit it?
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In this case the valve broke off and banged around inside the cylinder for a bit before it became lodged in the port.

The piston is all beat to hell. We’ll be replacing the whole jug.
 
Fearless Tower said:
In this case the valve broke off and banged around inside the cylinder for a bit before it became lodged in the port.

The piston is all beat to hell. We’ll be replacing the whole jug.
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That’s not what I meant. If the valve stuck open and the piston came up, would it hit? Some engines have clearance, many do not. If the valve stuck first and the piston hit it, the head may have broke off and proceeded to bounce around. It’s not uncommon to find them wedged in the port they came out of. You’ll also sometimes find a perfectly round hole pierced in the piston from the valve stem.

Many times the failures are catastrophic enough that a root cause can never be found, only speculated about.
 
What is the story, did you have to cage it? How far from the airport, not on takeoff or you'd be telling us about that!
 
Let'sgoflying! said:
What is the story, did you have to cage it? How far from the airport, not on takeoff or you'd be telling us about that!
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If happened in cruise. When it happened, the engine stumbled/burped just as if I had run the tank dry. That was my first instinct - to reach down and shift tanks, but then I remembered that tank was full and I’d only been running off it for 15 min.

After the initial burp, it just ran rough. Not horribly rough, but noticeable and the cowl was vibrating slightly. My wife (who usually freaks out about unusual sounds) didn’t even say anything.

I thought briefly about diverting (I was IFR) but everything else was normal. Power seemed matched between engines. Mags were both good. Props synced. No changes in oil temp or pressure. No really noticeable change in speed.

Having never experienced a failed valve, I started thinking that maybe an intake tube had come loose (happened before). So for better or worse, I made the decision to keep going home and watched it like a hawk to see if anything changed or got worse. It did not.

Even after we landed, I thought it was an intake pipe (left MP wouldn’t go below 25” at idle and on shutdown, we did indeed find a loose intake pipe. We didn’t find the valve issue until after we test ran the engine with the intake tightened.

In hindsight, had I known it was a valve, I probably would have diverted. Wouldn’t have caged it, but would have wanted to shut it down sooner.
 
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Fearless Tower said:
If happened in cruise. When it happened, the engine stumbled/burped just as if I had run the tank dry. That was my first instinct - to reach down and shift tanks, but then I remembered that tank was full and I’d only been running off it for 15 min.

After the initial burp, it just ran rough. Not horribly rough, but noticeable and the cowl was vibrating slightly. My wife (who usually freaks out about unusual sounds) didn’t even say anything.

I thought briefly about diverting (I was IFR) but everything else was normal. Power seemed matched between engines. Mags were both good. Props synced. No changes in oil temp or pressure. No really noticeable change in speed.

Having never experienced a failed valve, I started thinking that maybe an intake tube had come loose (happened before). So for better or worse, I made the decision to keep going home and watched it like a hawk to see if anything changed or got worse. It did not.

Even after we landed, I thought it was an intake pipe (left MP wouldn’t go below 25” at idle and on shutdown, we did indeed find a loose intake pipe. We didn’t find the valve issue until after we test ran the engine with the intake tightened.

In hindsight, had I known it was a valve, I probably would have diverted. Wouldn’t have caged it, but would have wanted to **** it down sooner.
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Good example of Dynamic compression.
 
Checkout_my_Six said:
where did you get that?o_O
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Think about it, it was still running. with the valve head stuck in the port, it was still making compression. It simply didn't have time to leak.
 
dell30rb said:
It is very reassuring to know that all of your CHT's and EGT's are in a good place when flying a piston engine aircraft.
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Yeah. I had a JPI in my Baron. It was helpful, but sometimes it’s too much info and you can start chasing temp variations that lead no where.

I kind of liked the old world simplicity that the Beech has....until now.

I have a 9 cylinder JPI in the T6 which has been very helpful.
 
Sorry about your valve/engine misfortune. Hope matters work out in short order..

I must say I worked on the DHC-2 for a while loved the R-985. Short story.

One of the line folks fueled A Beaver with Jet-A. Plane had about a 1/2 of tank 100LL mixed with 1/2 tank Jet-A. Flight was from Ketchikan, AK to Prince of Whales Island. Half way there CHT's started to run in the red. Pilot set it down in the channel, took 8 hours to get a boat out and tow him in. Flushed fuel system, drained the tank, did a test run up, no problems.
 
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