AMC v8s

What is up with the oiling issues in AMC v8s? I have a 81 cj with a 304 stock from the factory, This summer I had to replace the timing cover so while I was into it I replaced the oil pump, fuel pump, water pump and all the hoses, changed the oil and filter, didn’t any problems and guess what I drove about 250 miles and the motor locks up, on warning, no strange sounds, did not get hot, nothing, just will not turn over.

Did you prime the oil pump?

Sorry to say it - car ran from '81 to '09, then you work on it, then it locks up…and you think it’s an issue with the engine?

Those engines never had much of a reputation except for premature death, but in your case, the above post says it all…Stick a 258 AMC 6 in it and it will run forever…And drive better too…

Well, lets put it this way, yes I did prime the oil pump, fired the motor, it ran great with good oil presure, I drive the jeep for 250 miles both on and off road, with no problems what so ever, and it locks up. I have owned this jeep for 10 years and replaced just about every thing on it except the motor it’s self. I’m not going to proclaim that I’m the greatest mechanic in the world, but I’ve built race cars both Chevys and Fords, big and small blocks, sometimes things go wrong, and you break something, but not with out some kind of warning(even if it’s only a few seconds before it breaks) but not this time, not with this motor, nothing. If I did something wrong, (which I could have, although I don’t think I did) why did it have good oil presure and ran fine for 250 miles!

Sorry, more detail sure helps. Did it have good oil pressure even at the point of locking up? Do you have a gage on it?

A reminder that a couple years ago, my DIL’s car locked up, the starter would not budge it. Turned out to be a locked a/c compressor clutch. They disconnected the belt, which is possible on that car, and drove it across the US. The first mechanic said it needed a motor, the mechanic recommended on this URL under mechanic files, found the real problem. Do not assume motor problems; troubleshoot it.

When you say it locked up what did you mean. Do you mean it won’t turn over with the starter? Or do you mean it won’t turn over by hand with the plugs and starter removed. It is a Jeep, did you inhale a large dose of water and hydraulic lock it ? Did you remove the oil pan to see if the inside of the engine is junk ?

I have a gage on it and it showed 20 psi, while driving, no I was not looking at the gage the moment the motor quit, just driving down a dirt road at about 5 miles an hour, but I always look at the gages every few moments while driving, sure wish I was looking at it when the motor stopped. I have removed the stater and placed a breaker bar with socket on the crank bolt and can’t turn the motor.I have not inhaled any water, I will try the idea of disconnecting the belts.

"I have a gage on it and it showed 20 psi, while driving, "…

You should have at least 10 psi for every 1000 rpm…Sounds like you have a tired old Jeep with a tired old motor. Time to move on…

Since you are used to tearing into engines, it appears it is time to disassemble the engine and find out why it is locked up. You probably will be able to ascertain what went wrong by what siezed and the state of the contacting surfaces.

When you do find failed component, please post back to share your knowledge.

I’m with Researcher on this one. Since you can’t turn the crank with a socket and breaker bar, I’m betting you’re suffering from a seized crank/main bearing.

My guess is that you posted more for moral support than technical support. You have it.

Let us know what you find when you open it up. There’s a free muffin in it for whoever guesses right.

Before you start tearing the engine to pieces, pull the distributor and look for any obvious drive gear damage. The 304 front cover is made offshore by Crown and they’re known to be of ‘dubious’ tolerances resulting in dizzy drive gear destruction - apparently the problem lies in the oil pump drive alignment to the dizzy causing the cam / dizzy gears to self destruct after a few miles.

Sounds similar to your problem and could be the cause of the lock-up.

Crown supply these timing covers to jeep distributors, they seem to be the only remaining manufacturer for this part but it does need checking before installation.

I pulled the distributor and the gear looks fine, I could turn the oil pump shaft with the end of a screw driver. I then loosened the belts on the air conditioner compressor and could spin the clutch pulley. Short of tearing down the bottom of the motor I don’t know what else to do. Years ago my daughter had a wagoner that her grandfather gave her with a 360 amc motor in it. One day she was driving it and it just stopped running , (I had not worked on it at all, so can’t blame me this time) we pulled it home and the same thing I could not turn over the motor, pulled the starter, beaker bar with socket on the end of the crank no way could I turn it,I talked to several people and they brought up the point about how these motors lock up due to oiling passages being blocked and/or the oil pump going out I figured that the oil had not been changed regularly or the pump just went out. This is why I always changed the oil in mined and changed the pump while I was into it. I now, do not trust these motors they seem to be pron the this problems. I know that back in the day when amc was into racing they made good power and I guess they knew hoe to keep them together, but I have never had a chevy or ford lock up-with no warning, in fact never had any motor lock-up. I will pull this motor and in it’s place will go a TBI 350 chevy problem solved. So, back to my original question what’s up with the oiling system of amc motors?

I looked in a service manual for a 1975 AMC which had the 304 V8. That indicated that the oil circuitry is fairly straight forward. The oil is fed to a main galley that feeds each main bearing and the cam bearings. Oil is fed to the lifter galleys and from there up the push rods to the valve rockers ala GM V8s.

The only anomalies I noticed is that the oil pickup is in the back of the pan and crosses to the front cover. If the gasket in the front cover had a break it is possible that the oil pump could become air locked. Also the oil filter on this model is on the end of the oil pump cover. If doesn’t appear to have a weakness being there. The oil pressure sender is in the side of the block close to the oil pump so if there was a blockage further down stream it would not register it. Also it appears that the lower main shaft bearings are grooved probably because the main crank journals are not cross drilled. This groove reduces the load bearing capacity of the lower bearing possibly leading to a spun bearing.

Again, tear down this engine when you get it out. Eyeball the problem and get back to us to satisfy our curiosity. TNX

Your 28 year old engine gave up the ghost after you replaced some of its components? All I can say it it must have been one of the remaining original components. Buy yourself a new or rebuilt crate engine and get this old girl going again.

Rberry,if you tear into that engine I’d enjoy knowing what you find.