Bent push rod?

[Tidders]

We are based in the UK and have a 1959 Comanche 250 which is fitted with an EDM700 displaying exhaust gas/cylinder head temps for each cylinder. On a recent trip around Southern France and Spain we noticed that on cold start the display for #2 cylinder did not show up on the EDM. This appeared to clear itself after a couple of minutes and all power checks were good and when flying the cylinder showed temps in the normal range. It happened to 2-3 times on the trip but not when the engine was started when warm/hot.

Anyway we returned to the UK and have done a number of flights since then with no problems indicated.

Couple of weeks ago and shortly after departure and in the cruise the display for #2 disappeared from the EDM and the engine started running very rough with a lot of vibration. Returned to the airfield and the local maintenance outfit had a look and found a bent push rod on #2 cylinder (and also the the outer tube was bent). This was clearly the cause of the fault in flight and I guess the valve was sticking.

Has anyone experienced a similar fault and if so any advice out there on a possible cause would be much appreciated?

Note: For the last couple of years we have only carried out an oil change on the aircraft's Annual (fly about 70-100 hours per year) - previously we used to do it every 50 hours, could this be a contributory factor to the bent push rod?

Thanks in advance.

[Kristin Winter]

I think your oil change regime is problematic, though there is no way I can say for sure that it caused the problem. If you are not aware of this Lycoming Service Instruction, I recommend that you have your mechanic perform the check and ream the valves as necessary.

[Tidders]

Thank for you the info Kristin - will check with maintenance outfit.

[Clarence Beintema]

Your oil change interval is too long, oil changes are cheap when compared to other maintenance activities.
The symptoms you described are call "morning sickness" and started out only when the engine is cold, and eventually happens in flight. Reaming the valve guides per SB388 is the cure.

Clarence

[howard]

Have a close look, when this happened to me years back, it was. A bent pushrods and the tapped body was broken, that meant had to split case, therefore overhauled the engine. I had 300hour old brand new superior cyls that we had installed. My engine guy later (Bentima knows him) told me he always reams brand new cyl exhaust and intake guides as he often finds them too tight for his liking. I change my oil at less than 50 hours all the time. And sometimes closer to 30, and filter at the same time. We check the valve guides , and valve stems , and ream tight ones , if there are any,every 200 or so hours .... Have a close look at your Tippett or lifter body for breaks....