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Engine question PLEASE HELP!!

M

mattriddle

NAXJA Forum User
Location
Milton, ky..Madison, In
I have a 94, 4.0L and It runs flawless. No enging noise whatsoever, but when you rev it up, the crank actually moves out about 3/8", and when it idles back down it causes it to go back in. It makes the belt squeal bad. I've pulled and replaced the engine, but i need the engine for another Jeep. The motor is supposed to be a crate motor with under 5k on it.
Should it be an easy fix? Machining needed? Has anyone ever seen this before?
 
the crank is moving in and out of the engine? aside from being unlikely i think its physically impossible.

what IS possible is the harmonic balancer is seperating, and moving back and forth on the rubber dampning ring. can you actually see this back and forth movement? if so, double check to verify that the whole thing is moving, or if its just the outer ring of the balancer and the center hub is staying in the same position.
 
...anybody got pics of a 4.0 from the bottom with oil pan removed?

I haven't seen one from that angle, but maybe it's possible. It doesn't make sense though... craziness!

Seems like it wouldn't though, I'd throw a new damper on it and see if it helps.
 
mattriddle said:
I watch the crank, including the bolt come in and out. I can also manulaa do it by hand. It's not the balancer. I promise!!
Click to expand...
is the bolt itself loose? this really makes no sense to me. ship it to my place so i can get a better look at it :D
 
Crankshaft end play is 0.038 to 0.165 mm or 0.0015 to 0.0065 inch.

Even with complete failure of the thrust bearing I don't see 3/8" as possible. It would have self-destructed before that much wear could happen.

Pull the damper and inspect it.
 
ChevelleSSLS6 said:
...anybody got pics of a 4.0 from the bottom with oil pan removed?
Click to expand...

Yep, here's a shot of mine from a couple months ago. I don't see any way the crank can move that much.......
Jeff

rmsandpangasket.jpg
 
jneary said:
sounds like you have a bad thrust bearing
Click to expand...

Isin't the thrust bearing part of the rear bearing? And don't it have about 1/8" on either side of it? That is only 1/4" assuming it is lost completely which I think is highly unlikely.

The rear main bearing have a lip on both sides that fit snuggly over the bearing webb in the block. The other half of the bearing fit snugly over the main bearing cap. What I am trying to say is,...the rear main bearing hav a sort of 'U' shape that not only allows the crank to rotate in it but it also cradles tge crank from moving backward and forward. Unless both half of the bearing have these pieces missing it is unlikely the crank will move that much.

Sorry, sometimes it is difficult to get what is in my head on paper.
 
That is definitely messed up. The thrust is controlled by the by the width of the middle main bearing. Either that thrust bearing didn't get put in, and just a bearing like the others have or something else weird. Most of the main bearings are straight when looked at as a cross-section front to rear on the motor. The main with the thrust faces is "U" shaped. You got to pull the pan and take a look.
 
Some motors like the air-cooled Beetles were controlled at the rear and you would even add or take away shims in between the flywheel and the crank to bring end-play into spec. On most American style motors, it is controlled by a fixed size bearing on one of the central journals. If it's no good, you need a new crank. When we machined the thrust faces undersize in the block itself where the bearing went, sometimes (if you were running out of blocks), a weld repair to build stock back up was allowed and then remachined. The other surfaces and cylinder bores locations are all controlled back to the thrust face surface. But the crank rides on a u-shaped bearing that fits over the thrust faces in the block, and not the block itself.
 
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