Joined: Apr 26, 2017 Posts: 50 Location: Butler pa
Posted: Tue May 24, 2022 7:18 am Post subject: Push rod Issues. M38a1
Started my rebuilt engine. After 5 minutes, running started to tap. #1 cylinder push rod failed, and the top of it mushroomed. Now rocker is not making contact with it. (Pic)The #1 cylinder is on its intake stroke, going down almost at its furthest downward point and still not making contact with the pushrod.
Again I am not a mechanic and have a guy helping with this. It takes me awhile to figure things out with books and help from here. That being said.
There is a lot of play in the pushrod. I think I read it right that there is a solid lifter, pushrod, rocker, valve, and camshaft. What drives the pushrod is the camshaft; the push rod sits on top of it, correct?
Also, is this just fix of replacing the Pushrod and adjusting the valve? Or is there more to it. Any help would be helpful.
My mechenic is looking at the books and can't get the answer..
You can open the link above the photo to find other great information in Wes' albums.
Now in all honesty, I've never worked on an F134 and I've only ever stood in front of one briefly. What I'm about to say is just what I can ascertain from the diagrams I am linking in this post.
The lifters are what ride up and down along the lobes of the cam. Their job is to:
lift the exhaust valves directly, as the exhaust valves are located in the engine block with their stems facing downwards towards the lifters,
and
lift the intake valve pushrods, as the intake valves are located in the engine's head with their stems facing upwards.
The intake valve pushrods then contact the rocker arms, which are what you took a picture of under your valve cover. From that picture, it looks like your pushrod is pretty good and rounded off, and I'm going to throw some darts at the wall for guesses in no particular order:
valve adjusted with too tight of a gap. Metal expands with heat, and as the engine warmed up, if the pushrod was set too tightly, the pushrod had no room to expand and wore itself down against the rocker arm.
lifter is stuck and is not travelling up and down with its respective lobe on the cam. This is what Mike_B is referring to when he said that you could have "wiped the lobe on the cam". If the lifter won't move, the cam shaft was definitely moving while the engine was running, and its possible that the bottom of the lifter destroyed that lobe on the cam, or at the very least the lifter got itself destroyed by that cam lobe.
rocker arm shaft bushing is worn, allowing the rocker arm to tilt and contact the pushrod at an angle, possibly mushrooming the end. This is the picture below from Wes' album.
You're going to need to explore some more before coming up with a definite answer as to what went wrong, but I can say two things for you as if this were my own engine:
1) You should not try to replace that one pushrod and run the engine, as the pushrod was probably not the problem, it is merely a symptom of a larger issue
2) You should be prepared for the possibility that you will have to disassemble the engine and at the very least expect to flush out any metal particulate that came off the top of that pushrod, again with no definite knowledge of that caused the damage.
Sorry if this isn't what you want to hear, and again take my advice with a grain of salt as I've never worked on your engine. I'm simply commenting from a place of general engine knowledge and hoping to steer you towards a possible cause of your damaged pushrod.
~Jake _________________ Jake, Central CT
51 M38 s/n 35627
Joined: Dec 10, 2017 Posts: 349 Location: Southern Maryland
Posted: Tue May 24, 2022 4:39 pm Post subject:
There are many ways to "wipe a cam lobe" (take the top off of the egg shaped cam lobe) making it not able to push the lifter high enough to open the valve and subsequently letting the pushrod cup fall out of the rocker ball causing it to do what your engine did. I'm not saying your cam is wiped, but if it were me I'd pull the side cover and turn the engine by hand and confirm that that lifter is still going up and down to the same height as all of the others.
The other cause could be improper rocker arm/valve adjustment, it does look like there is a lot of thread sticking out above the jam nut.
Is this a FRESH rebuild with new cam and lifters? If not, did you take the lifters out and make sure they went back in the same hole?
If you have a new cam, did you do a break-in run to work harden the cam and lifters?
Mike B _________________ Mike B
1953 M38A1 Brush Truck
1952 M38
1951 M100 Trailer
Joined: Apr 26, 2017 Posts: 50 Location: Butler pa
Posted: Tue May 24, 2022 10:27 pm Post subject: Engine
The garage that rebuilt it, rebuilt it entirely. I do know that they put it together wrong for the fact it was out of time and the oil pump timing was off and a few screws were loose. I will print these replies off so that when I go out we can talk about what to do. I did order a new pushrod but with the three-day waiting for it to come in, we can look at the other suggestions to the issue.. Again thanks. I know I ask alot of simple things on here, but trying to find my way. A Old dog trying to learn about the hobby.
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