M151a2 engine question.

elkhtr · Sep 13, 2014

poppop said:
elkhtr, I just repaired an engine in an A2 for SS member grits with the same problem, only it was one valve. Check the valve adjustment screw in the affected rocker arms. They are supposed to be hard to turn and have no lock nuts. In Andy's engine that screw was real loose and backed out until the push rod jumped out of the rocker. It did not jump clear but bound up on the edge of the rocker which I think caused the valve to hit the piston. This broke the head off the lifter. It had run so long like this the broken stem had cut a quarter inch groove in the cam. I pulled the engine, stripped the front and held the lifters up and removed the cam and replaced the broken lifter and installed another cam. Also replaced the defective rocker. It runs like a champ now. Unless you have a bent valve from hitting a piston I think your engine is very repairable. I got Andy's parts from an engine I had bought for parts. I don't have another cam but I do have the lifters and rockers if you need them.

Hi poppop,
I think I will pull the engine and do some looking.
The rockers looked good, but I might need to take you up on the lifters.
This being my first solid lifter vehicle, is it a no-no to use lifters that werent broke in on this cam, assuming the cam wasnt destroyed?

poppop · Sep 13, 2014

Elkhtr, I don't think it would be a problem at all. I only replaced the broken lifter in Andy's engine instead of changing them all even though I changed the camshaft with a used shaft. If there is any problems I think they will wear in to each other. You may have to adjust the valves again after it runs a while. You will have to drop the oil pan and remove the oil pump to get the cam out. Be sure you don't turn the engine or oil pump shaft once pulled and you won't have to time the engine again. But before you pull the oil pump line up the timing marks on the timing gears so if the cam has to come out you can put the replacement in correctly. The one with the bent pushrod hopefully bent the rod instead of a valve. Both damaged ones should be exhaust valves as they are the only ones that can hit a piston as they close as the piston is at the top of the cylinder.

poppop · Sep 13, 2014

I just did a quick ebay search for M151 camshaft and found two, one used in North Carolina for $65.00 and an NOS one in Ga for $100. The guy in North Carolina states he is selling all his 151 parts including surplus engines.

elkhtr · Sep 13, 2014

poppop said:
I just did a quick ebay search for M151 camshaft and found two, one used in North Carolina for $65.00 and an NOS one in Ga for $100. The guy in North Carolina states he is selling all his 151 parts including surplus engines.

I saw those but the rust on the bearing journals scared me a bit on that new one.
When I was younger I used to do quite a bit of high performance gas engine stuff.
A lot of the cam rules from that are stuck in my head.
Keep lifters matched to the lobe they ran on, etc, etc.
Just need to get over that I guess.

Jeepsinker · Sep 13, 2014

Yeah none of that stuff applies to the military equipment world. If your lifters were torn up that bad the cam is almost certainly shot as well.

elkhtr · Sep 14, 2014

Jeepsinker said:
Yeah none of that stuff applies to the military equipment world. If your lifters were torn up that bad the cam is almost certainly shot as well.

In the process of pulling the engine now.
the cam lobe with the broken lifter doesn't look bad shining a light down the lifter bore.
We will know more once the engine is out.

elkhtr · Sep 14, 2014

Engine pics

Got the engine out, cam looks ok, cylinders still have crosshatch showing, no sludge build up.
Found the two broken lifter heads in the oil pan.
Pretty obvious that the center two cylinders haven't been firing in a while.
I am thinking of just replacing the damaged parts and seeing what happens.
The pictures of the cam are the lobes that the broken lifters were riding on.
Didn't see any other damage that stuck out.
What do you guys think?

Jeepsinker · Sep 14, 2014

Replace the bad parts and run it.

poppop · Sep 15, 2014

Yep, replace the broken parts and run it. Let me know what all you need. Double check the valve adjustment screws. The manual gives a torque spec that it should take to turn it. Any less and replace. I still think thats what caused the damage.

elkhtr · Sep 16, 2014

poppop said:
Yep, replace the broken parts and run it. Let me know what all you need. Double check the valve adjustment screws. The manual gives a torque spec that it should take to turn it. Any less and replace. I still think thats what caused the damage.

I am in the process of gathering parts as we speak.
Poppop, I definitly appreciate your offer of help with the parts but so far I am finding what I need without troubling anybody.
Somebody posted that they thought the exhaust valves stuck from sitting, I think that diagnosis was probably correct.
If nothing else I will get good at pulling this engine, got all winter to figure it out.

Lindsaym151 · Sep 17, 2014

Easiest engine to pull .Did mine 7 times in 2 days! Fastest time was 45 minutes going in!

Jeepsinker · Sep 17, 2014

7 times in two days? What happened? You know you aren't supposed to use coke can pieces for rod bearings....

Whiterabbit · Sep 17, 2014

Little tidbit I found out.
Make sure you chase the threads for the head bolts. The guys that mess with these engines say the head bolt threaded holes near the back of the block are sometimes short on threading. Something about the holes weren't threaded deep enough and the head bolts bottom out on some engines. I chased/cut mine with a bottoming tap prior to tossing the head back on.
I also taped the top of the block up and took a pressure washer to the water passages to remove any rust/sludge in the cooling system.

elkhtr · Sep 17, 2014

Whiterabbit said:
Little tidbit I found out.
Make sure you chase the threads for the head bolts. The guys that mess with these engines say the head bolt threaded holes near the back of the block are sometimes short on threading. Something about the holes weren't threaded deep enough and the head bolts bottom out on some engines. I chased/cut mine with a bottoming tap prior to tossing the head back on.
I also taped the top of the block up and took a pressure washer to the water passages to remove any rust/sludge in the cooling system.

Thanks for the tip.
None of the bolts I removed showed any signs of a short threaded hole, but easy enough to check now.
I like the pressure washer idea, when I rolled the block over on the engine stand I did get a little slurry out of the passages.
Kind of surprised the pressure washer didn't blow the tape off the top of the block though.

Whiterabbit · Sep 18, 2014

I just taped up the cylinders and oil passages. That crap came flying outt'a all those water passages! I pulled my head thinking I had a blown head gasket/over heating. Nope. Bad timing. LOL!

elkhtr · Nov 22, 2014

Success!

Sent the cylinder head to the shop to be freshened up.
Replaced the broken lifters and bent pushrods.
A good cleaning, and there you have it, purrs like a kitten.
While the engine was out I did full fluids and lube.
Replaced the rear differential with a NOS unit and put on new tires.
Flushed and adjusted the brakes, one line was plugged.
It is a whole new rig now.
Drives straight and quiet (for a mutt).
Now back to the deadlined m923.

Flyingvan911 · Jan 11, 2015

I'm searching for the stock cylinder bore for the Mutt engine. My cylinders are about 3.910 inches at the bottom of the piston stroke. The top of the cylinder is 3.90. I am doing some engine work and trying to see what's what with this particular one. The TM's I've looked at don't have the table that is supposed to have the info. Searching the site here didn't turn up any threads with the measurement.

poppop · Jan 12, 2015

My book says 3.875.

Flyingvan911 · Jan 12, 2015

Thank you very much!

M151a2 engine question.

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