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