Valve Lifter Push Rod Blown

[CHARLES DEBOER]

Does anyone know why a valve lifter push rod would come off rocker arm and jam next to the rocker arm after only seven hours and thirty minutes of run-up and taxi time?

[Steve]

Does anyone know why a valve lifter push rod would come off rocker arm and jam next to the rocker arm after only seven hours and thirty minutes of run-up and taxi time?

Jam nut on valve lash screw not snugged down...

If Milholland conversion see if the rocker arm stand is still in place and no flaws/cracks etc...

Bent pushrod, - an assembly error... Any bend is a no-go...

Pushrod initial length adjustment assembly failure...

Rocker arm to valve stem angle wrong...

Pushrod tube rubbing on pushrod...

Piece of junk traveling around in the case or oil galleries...

Broken lifter or cam lobe failure...

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Put it back together and see if the valve action is true - go on from there and run engine briefly with rocker cover off - look closely at the pushrod to rocker arm join for alignment..

[joecnc2006]

I had gotten my heads and rocker arm assembly from Casler, and i did notice that they are not pinned or locked from rotating, i would check to see if they may have rotated off the stem you may need to drill the 1/8" hole for a role pin or make an additional bolt on the end.

[Steve]

I had gotten my heads and rocker arm assembly from Casler, and i did notice that they are not pinned or locked from rotating, i would check to see if they may have rotated off the stem you may need to drill the 1/8" hole for a role pin or make an additional bolt on the end.

Casler does rocker shaft different - rocker arm positioning still applies...

[Dan_]

I had gotten my heads and rocker arm assembly from Casler, and i did notice that they are not pinned or locked from rotating, i would check to see if they may have rotated off the stem you may need to drill the 1/8" hole for a role pin or make an additional bolt on the end.

Casler does rocker shaft different - rocker arm positioning still applies...

The best I recall Casler leaves the rocker shaft somewhat longer so that it can be secured at the cut end, making the roll pin unnecessary, and is probably a more secure way of doing it but no doubt a little heavier.

[joecnc2006]

Does anyone know why a valve lifter push rod would come off rocker arm and jam next to the rocker arm after only seven hours and thirty minutes of run-up and taxi time?

Do you happen to have a picture what your rocker assembly looks like.

Here is mine so far. have to see if i can find pictures how to secure it.

[Dan_]

Ala Casler...

[stevejahr]

Normally if everything is adjusted right and aligned right... the valve spring keeps things all connected.  So make sure that valve is not sticking and allowing things to get disconnected.

[CHARLES DEBOER]

Does anyone know why a valve lifter push rod would come off rocker arm and jam next to the rocker arm after only seven hours and thirty minutes of run-up and taxi time?

Do you happen to have a picture what your rocker assembly looks like.
Yes, See attached photos.  Believe it or not the engine continued to run on one cylinder.

[Tom H]

Here is a possibility, if you are using the swivel foot rockers.  By that, I mean the ones that have the flat-sided ball that contacts the tip of the valve stem.

If the ball's flat side was not properly positioned on the valve stem tip when clearances were set, and then, when running, the ball's flat moved into correct position to contact the valve stem tip, clearance would become excessive, and the pushrod could possibly slip out of the socket in the rocker.

Something to consider?

[CHARLES DEBOER]

Here is a possibility, if you are using the swivel foot rockers.  By that, I mean the ones that have the flat-sided ball that contacts the tip of the valve stem.
If the ball's flat side was not properly positioned on the valve stem tip when clearances were set, and then, when running, the ball's flat moved into correct position to contact the valve stem tip, clearance would become excessive, and the pushrod could possibly slip out of the socket in the rocker.
Something to consider?

Scott said that he got some push rods that weren't heat treated, which caused a deformation of the push rod which created a larger gap between rocker arm and push rod so it slipped off rocker arm.  He said that there would be no damage to the valve or cam shaft.  Just replace it and re-gap and I should be good to go fly.

Should I be nervous?

[stevejahr]

Hmm.

I would wonder about the suppliers he is using... and if one pushrod was wrong I would wonder if other pushrods are wrong.

I would want to inspect the cam/lifter personally to verify.  It operated for some cycles with excess slop so the normal transition ramp on the cam profile was skipped.  So the takeup would have been more abrupt than was intended/designed.  And early cycles are the most critical when the can/lifter are seating.

I would also want to closely inspect and measure all the pushrods to make sure there are no others suffering this problem.  I might even go so far as to say 'pushrods are cheap' and replace them all.

Then I would be checking these things after every flight for a while until I got comfortable with them.

[CHARLES DEBOER]

Scott at Hummel Engines replaced all of the push rods.  Just had to pay $130 shipping one way.  Turn around was two weeks LA to Phenix total.
Now I am having trouble getting the carbs sync'd. 

 DOES ANYONE HAVE A GOOD METHOD FOR TUNING THE HUMMEL TWO CYLINDER 45 HP VW WITH TWIN MEKUNI VM28s??