Pushrod failure - unknown cause

[Guest]

It possible that a failed hydraulic valve lifter caused the rocker arm clearance to increase to the point that the pushrod started hammering on the rocker arm leading to failure of the pushrod and rocker arm.   Failure of the pushrod with the end falling off then the broken end jamming the intake valve and bending the pushrod makes complete sense.

In many cases sticking valves can lead to pushrod bending and failure on start up, in steady flight is more rare, although not impossible.  I had it once on my E model on power reduction for descent and landing.

Following up on Rich’s suggestion of running the engine with the rocker cover off, you could leave it on but remove the oil return line and put a hose in its place.  Run the hose into an old oil container to capture the oil.

I remember a story of a Grumman Tiger that kept having exhaust valve failures.  The own found a large difference in oil flow to one side of his Lycoming factory reman by capturing oil from the return tubes to prove to Lycoming that there was a flaw in the engine oil system.

Clarence

[RDuplechin]

Thanks Clarence.  I’m going to mention this technique to the guy doing my annual and ask him to make sure all cylinders seem to be receiving a similar quantity of oil over a given period of time.

 

I was wondering why someone hasn’t fabricated a diagnostic valve cover with a window or large sight glass to visually verify oil is moving to the top of the cylinder.  It seems like for short periods of time it would be feasible.

[Guest]

17 minutes ago, RDuplechin said:

Thanks Clarence.  I’m going to mention this technique to the guy doing my annual and ask him to make sure all cylinders seem to be receiving a similar quantity of oil over a given period of time.

 

I was wondering why someone hasn’t fabricated a diagnostic valve cover with a window or large sight glass to visually verify oil is moving to the top of the cylinder.  It seems like for short periods of time it would be feasible.

That’s a neat idea! A plastic window or 3D printed from clear material if that’s even possible.

Clarence

[RDuplechin]

That’s how I’ll make my fortune!   LOL

[Prior owner]

38 minutes ago, RDuplechin said:

I was wondering why someone hasn’t fabricated a diagnostic valve cover with a window or large sight glass to visually verify oil is moving to the top of the cylinder.  It seems like for short periods of time it would be feasible.

I think the reason is because nobody really wants to stand that close behind A running prop to watch the rocker arms moving...

[carusoam]

We have a baby food jar test for fuel injectors...

We could easily develop a similar baby food jar test for oil return/delivery lines...

 

From a single experience... with my O360...  one stuck valve... stuck open... leaves a half-moon shaped indentation in the top of the cylinder... trashing a few things in the valve train...

A decent dental camera will make nice pics of it...
 

My simple experience resulted in tossing the cylinder, retaining the piston with its tattoo....

Fuzzy PP Memories of times long ago...

Best regards,

-a-

[RLCarter]

 

 

[RDuplechin]

For those still following along...the consensus seems to be that the exhaust pushrod tip failed first.  This could be because the valve stuck.  When this happened the chamber could not be emptied and was highly pressurized.  The intake valve is designed to open into an empty cylinder not push against a high pressure.  When the intake tried to open the weakest link failed and the intake pushrod bent.  The failed mag may or may not have played into the failure sequence.  
 

The next step is to check each cylinder to ensure good oil flow by hooking up a tube where the oil return line goes in and running the engine to see if all are flowing similarly.   I may also use Avblend moving forward.  May be snake oil or it may help.  I don’t think it will hurt anything.  Any other thoughts on how the operator can avoid sticking valves?

[carusoam]

Use a good oil...

Fly often...

Change oil often...

Keep CHTs under control... always...

Check you engine monitor data routinely...

Pray to the proper god of aviation‘s rotating hardware...  Not the other one...

Raise a stack of cash... for a replacement engine...

 

Know the sooner you have the stack of cash raised, the less likely you are to ever need it... 

The most important thing, is the fly often part...
 

Best regards,

-a-

[PTK]

On 6/29/2020 at 12:13 PM, RDuplechin said:

Any other thoughts on how the operator can avoid sticking valves?

The single most important thing is keep CHT’s cool, <400° F. I suppose avblend doesn’t hurt anything but high CHT with overly rich mixtures definitely does.
In my mind the question is not if avblend hurts anything, It’s 99% mineral oil... and at a cost of 43$ per quart, some real expensive mineral oil! That’s more than 8 times what my Aeroshell 15W50 costs! Mineral oil is what our engine oil is made of. So of course it doesn't harm. But that’s not enough for me. The real questions are: does it help? and if it does how can you verify? I’m not at all convinced that it does anything useful. The fact they were sued for deceptive advertising and had to settle a 1 mil $ lawsuit doesn’t help either.

[ArtVandelay]

Any other thoughts on how the operator can avoid sticking valves?

MMO. Add 1/2 qt on the pre oil change flight.

[skykrawler]

The engine could have been assembled with incorrect dry tappet clearance.  Correct push rod length must be selected if components change (cam, lifter, tappet, rocker).

I know of a recent O-320 that had a very similar thing happen within 50 hrs of field overhaul at an 'engine shop.'  It also bend the tube and leaked out a lot of oil.

[cliffy]

We have two supposedly independent systems that failed on the same flight- ignition and valve train

To have two independent system failures at exactly the same time seems in-congruent

Were the failures independent or concomitant with each other?

Can a mag failure cause a valve train failure?   Hmmm   Or vice versa?

Left mag failed  What/who determined that the left mag failed? 

What was the mag failure diagnosis? What failed in the mag? Was the mag bench checked after the incident to verify it failed?  Was it visually inspected to find internal failure?  Or was it just a guess that it failed? 

Independent of everything else one mag failure won't kill the engine. That is why we have two mags (dual mags included unless a drive failure is involved)

Valve rocker pocket wear ? Dry valve clearance on assembly? Lack of oil? 

I'm going on the idea that to have two independent system failures at the same exact time is virtually impossible unless a common thread can be established which I din't see right now. 

I'm not sure of the mag failure with what is written in the first posting (unless I've missed something). 

I'm more apt to believe that it was a valve train failure rather than a dual system failure. I'd like to see the mag inspection and test after the failure report.