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Pushrod failure - unknown cause


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I recently had two pushrods fail on the same flight.  No one is sure exactly why.  I throw it out to the group to see if anyone has had a similar experience.  I was flying my 65E to annual in central TX.  The flight was to be about 1+15.  I was at 7500’ leaned 50 ROP and the engine was smooth as a sewing machine.  I’ve had the airplane a year and the engine has roughly 170 hours on it.  40 to 45 of those hours are mine with no issues and good mag checks on every flight.  About 50 minutes into the flight I get a violent vibration like I just lost a cylinder.  All temps and pressures are good.  No visible fluids on the windscreen.  I glance at ForeFlight and there is not a single spot of magenta in my glide ring if the engine dies.  I start troubleshooting.  I’m still on the same fuel tank but I switch anyway.  I work mixture, rpm, etc to see if any of that helps.  Admittedly, I did not cycle through the mags.  I reached for the key and then just stopped.  A rough running engine seemed like a better alternative to a non-running engine with no airport within glide range.  For about 30 seconds I thought seriously about trying to make my destination since I’m a short distance and I know there is maintenance.  Then I had a vision of all the guys I served with shaking their heads at my wake saying, man he knew better than that!  The closest airport was about an 8 minute flight off my right wing.  I turned to it with about a 400 fpm decent and a worsening vibration.  I never heard the backfiring but it was heard from the ground, I’m told.  The noise cancelling headsets block that out pretty well too apparently.  I called one of the three airplanes doing pattern work and asked if there was maintenance at the field.  He said there was and he made a phone call for me to alert a mechanic to meet me.  I made it to the field still about 3000’ AGL (intentionally) and then spiraled down to land.  The engine quit taxing to the ramp and we had to push it into the hangar.  It would not restart.  In summary, compression was fine, plugs looked OK.  Left mag failed.  
 

I’ll deviate at this point to say that 80% of my time is in turbine engines but I thought the whole point of dual mags was that if one failed the other kept the engine running.  That most assuredly was not what I would describe happened to me.  A logbook check revealed the mag would have been changed at annual anyway.  It was past 500 hours.  After the overhauled mag goes on, the engine won’t start.  Now the doghouse gets removed where it is found the #4 intake pushrod and tube is shaped like a banana.  Thankfully, it didn’t punch a hole in the tube and blow all the oil out.  Off comes the jug to Inspect for further damage.  The piston and valves are fine.  No corrosion and the cam and lifters are fine.  But they do find the exhaust pushrod is broken and the exhaust rocker arm pocket (where the rod end goes in) is wallowed out. All that is fixed but the question remains...Why?
I’ve involved 4 different mechanics and no one has has a good idea of what failed first and in what sequence.  One theory was I don’t lean aggressively enough on the ground and a valve stuck.  The problem is I do lean until the engine stumbles while on the ground and we checked all the valves and valve guides. All are clean and not bent.  Another theory is that the mag failed first and it threw the timing off so badly that combustion alone drove the intake valve back up against the pushrod bending it.  A yet a third theory is the exhaust valve just broke and put the whole valve train in a bind bending the intake side.  The bottom line is it is supposedly fixed, I have a new mag, and the airplane made it the last few miles into annual.

 

I’ll get my popcorn now and standby.  Seriously, if anyone has heard of anything like this and can advise on other possibilities, please let me know.  All I know is I’m 3K lighter and still not confident that the root cause has been addressed.  I’m flying her to Montana in September and she is not an impressive performer on 3 cylinders over flat ground...I’d rather not repeat over the mountains.  Thanks for any thoughts.  I have pictures if anyone is curious 

 

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I have had this happen, It is not a pushrod failure it is stuck valve. The question is why did the valve stick?

After completely reading your post (sorry), it sounds like you had an oil failure. The valves are oiled by oil from the lifter being pumped through the push rod, through the rocker arm and then splashed out the rocker arm shaft. For some reason, the oil wasn't flowing. That caused the rocker socket to wear and get galled and the lack of oil caused the valve to seize.

It was probably caused by some debris plugging the oil path somewhere.

Sorry this happened.

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I don’t see a misfire/detonation event causing pushrod bending... Unless it was prolonged and led to overheating of the valves. Do you have any more data (engine monitor)?
 

On a side note, I witnessed a magneto failure that caused a complete loss of engine power. Some of the internal timing gear teeth broke, the timing severely jumped, causing the affected mag to fire the plugs at a position that was so far advanced that it ignited the mixture while the exhaust valves were still open. It backfired and shook horribly, produced almost no power but continued to run. My faith in the dual magneto concept was shaken that day...

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It is unlikely that engine monitor data would show anything.

It is possible that the rocker seized instead of the valve, but its shaft floats in the head and in the rocker and it would have to seize in both places. The thrust washer may have seized, but all that would have been obvious.

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1) Good job of getting on the ground safely...

2) Mags get OH’d at 500hrs by choice of many people, not a requirement...

3) there are certain Mag failures where turning off the bad mag is much better than leaving it mis-operating.

4) Coked oil in the valve guides can block oil paths... look for baked black carbon left in the valve guides... (exhaust valves can get really hot)

PP thoughts only, haven’t seen the banana-ized push rod covers before...

Great pics and description.   Inviting @M20Doc to the discussion...

Best regards,

-a-

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MKTurbo, I was not present when the damage was found.  I can’t speak to how it was installed.  The mechanic did not mention any hardware being reversed on teardown and I would assume he would when I asked him why did this happen?  He had no answer.  

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Carusoam,

#3 Agreed...and I almost checked the mags.  I didn’t because I wasn’t over any terrain I wished to land on.  The closest airport was several miles beyond my glide range.  I could find the good mag or it could quit entirely.  I wasn’t confident that if it quit I could get a restart.  I’ve gone back and forth 2nd guessing trying the mags but I probably would do it the same way again.  Partial power is better than dead silence when there is nothing below me.  
 

#4. We thought that might be the issue but can find no evidence of that. Valves and guides were super clean...no evidence of coking.  If they stuck in flight they had cleaned themselves upon landing.  No distortion, no burrs or nicks, no bent or tweaked valve shaft.  I did not tell the guy how much time was on the engine but I asked him to borescope everything while the jug was off.  He called me and asked if it was right out of overhaul it was so clean.  
 

Comments about lack of oil have me intrigued.  The airplane came with XC20/50 and Camguard.  (It lived in Wisconsin before me, not flown much in winter, and the previous owner thought Camguard a good idea.).  Don’t want to start a Camguard debate...I know there are passionate opinions pro and con.  I just mention it to illustrate what was in the engine at failure and ask would Marvel MO be a good idea if it is suspected that  a lack of oil to the rockers was the culprit?  I’ve heard it said some people swear by MMO in Lycomings.  I’ve used it in old cars for many years but never in an airplane.

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6 minutes ago, RDuplechin said:

RLC.  I can’t disagree.  Did the mag set off the whole chain or was it simultaneous failures then?

Back to the chicken & egg.... not knowing how the mag failed it’s hard to say. Finding out what failed can be found by most A&P’s, diagnosing why it failed needs to start as things are being removed. I am not an A&P but I have seen tons of broken parts over the years, looking at what has been posted, the worn rocker allowed for the pushrod to move around and eventually break, the broken tip jammed the other valve bending that pushrod. As for the mag, 2 separate failures are possible but the violent shaking probably took out the mag. By the way, looks like your bird rolled out a short time after mine 

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I have seen the tabs on the rocker cover brake. Then the rocker pin drops out and causes a chain of events. 
The metal tab work hardens then cracks at the weld. 
Rocker covers should be inspected periodically. As there is nothing that calls for the inspection until overhaul. 
-Matt

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I have had 3 magneto failures. I failed to switch to the good mag each time even though it states to do so in the POH. I was to preoccupied with the rough running engine. 2 of the 3 times EGT’s and CHT’s went wild with backfiring during these 2 times Luckily I was still in the pattern of the airport. If I continued flying I could of easily lost a cylinder and had more serious issues to deal with. The 1 time that the EGT’s and CHT’s didn’t go wild on the mag failure I was on a 3 hour cross country the engine was smooth and didn’t even know the mag was out. The only thing I noticed was that EGT’s we’re slightly higher than normal but when I was landing I was getting some stumbling I’m sure because of an overly rich mixture. It was diagnosed on the ground the the mag had completely failed. The difference on this failure was it was the 1 mag was completely out, similar to if you turned it off in flight. I recommend people isolate and turn off the bad magneto regardless. 

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Could the backfiring or miss timed ignition have caused the push rods to bend? Mag failure could significantly change the timing on an individual cylinder. If ignition happened at the correct point it could put a lot of pressure on the valve bending the push rod? Just thinking out loud.

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Lots of good comments here. One thing doesn’t add up to me. If the push rod fell out of the socket certainly the valve would hit the piston right?  At least it’s this way in most automotive engines I’ve worked with. It causes the valve to over travel. Maybe in this engine that isn’t a risk. Makes me think the valve stuck, bent the push rod, then the rest is progressive damage.

Valves can stick if things get too hot.  This can be from too much heat added or not enough leaving.  Lack of oil is a strong possibility.

Without having parts in hand to look at it’s tough to say  

 

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