Has this ever happened to you?

Dr. Bert · Nov 6, 2008

The H I am working on suddenly started missing after a very loud "backfire". Checked the plugs--#4 was wet. Put in a new plug--same miss. Ran a compression test--#4 had no compression--all others 120#. Pulled the valve cover and found that one push rod had "jumped" out of the tappet. The push rod was very slightly bent, but I don't think it was enough to slip out of the tappet. All I can think of is that that lifter was set up way too loose when last adjusted (not by me). All the others were set at 15/1000. What do you think caused this? Thanks.

farmhand · Nov 6, 2008

Bert not anything out the ordinary I have had many do the same thing. I would try to find a straight push rod to replace with. I had one come off before and push through the tappet cover.

Paul in MN · Nov 6, 2008

It is possible that the adjustment screw on the rocker arm has loosened.

Or the rocker arm was not getting proper oil and the bushing on the rocker arm has badly worn.

Or the valve spring has broken so that the tappet was being slapped hard by the cam lobe. If spring is broken, the valve does not follow the cam so there may be too much slop in the push rod and it jumps out of place.

This same thing happened to my 401 Ford 9000 diesel...valve lash adjustment screw had backed off, the push rod was badly bent. It sure sounded bad, and it was very sudden. We towed it home to the shop.

Good luck,

Paul in MN

Dr. Bert · Nov 6, 2008

Thanks to Paul in MN and Farmhand. I do have extra push rods so will replace the "bad one" with one of those. Spring, rocker arm, and tappet all appeared to be normal and tight. That is why I am mystified.

Duner Wi · Nov 6, 2008

Check compression on bad push rod cyl. when you put it together. I am wondering if you could have a sticky valve due to carbon build up on stem.

Andy Martin · Nov 6, 2008

I had one come off on an H. I straightened it, adjusted the tappet, and it has stayed on for fifteen years or so. I think mine just bent and jumped out, but it straightened ok.

Dr. Bert · Nov 6, 2008

DunerWI-- I did check the compression after the repairs and it was up with the others--120#. Thanks for the tip.

rustyfarmall · Nov 6, 2008

It is possible that particular valve is a bit sticky in the guide and at one point did not return to fully closed, which creates quite a bit of "slop" in the valve train. I had the same thing happen about 9 years ago while getting an H running again after it had sat for several years. I pulled the bent pushrod out, layed it down on a hard, flat surface and hammered it until it was straight again. That H gets regular use in the summer months and has never given me a lick of trouble.

Has this ever happened to you?

Dr. Bert

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farmhand

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Paul in MN

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Dr. Bert

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Duner Wi

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Andy Martin

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Dr. Bert

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rustyfarmall

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