Crankshaft moves in and out

J

Jaymoor911

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Joined
Sep 21, 2020
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4
Location
Texas
I am getting ready to pull my 4.0 out for the third time out of my 1999 tj. The first time it came out it had a rod knock so I had it rebuilt by a buddy who has done many 4.0 motors. Not a year later my tranny went out and we pulled it but come to find out we were able to move my crankshaft a 1/4 inch in/out ward. We pulled the motor back out and had it fixed via new crank (turned & polished) and new bearings. Well it’s been a good 5 months and I believe we’re having the same issue. Any ideas as to why this is doing that?
 
The thrust bearing is what controls forward/ aft movement of the crank. If you have 1/4" of linear movement that sounds like the thrust bearing has to be nearly wiped out. You can see what's going on by popping the oil pan and get a rough idea with a feeler gauge.
 
Crankshaft end play spec is .0015-.0065. Number 2 main bearing is your thrust. Remove the oil pan and number two main bearing. Inspect the bearings and thrust surface of your crankshaft.
 
I didn't check your profile but do you have an automatic? Did you possibly replace the motor with one from a manual? Is your torque converter hub pushing against the pilot bearing that was likely still in the crankshaft? This would certainly eat the thrust bearing, but would also probably give you auto trans pump problems.
Just a thought.....

Oooops, sorry, I see you rebuilt your original motor. This is probably not applicable in that case unless he installed a used crank from a manual trans....
 
TjSteve0305 said:
So your crank was turned and polished, not replaced, correct?

Did you seat the thrust bearings upon assembly and measure crank end play?
Click to expand...
No We bought another crank and then had it turned and polished.

I’m not 100% sure, we had it sent out to get re done
 
hardtailpan said:
I didn't check your profile but do you have an automatic? Did you possibly replace the motor with one from a manual? Is your torque converter hub pushing against the pilot bearing that was likely still in the crankshaft? This would certainly eat the thrust bearing, but would also probably give you auto trans pump problems.
Just a thought.....

Oooops, sorry, I see you rebuilt your original motor. This is probably not applicable in that case unless he installed a used crank from a manual trans....
Click to expand...
It has original motor and when it threw a bearing we had it rebuilt, shortly after the transmission (3 speed auto) was rebuilt. Upon inspection the crank moved 1/4” so we pulled the motor back out and got the bottom end rebuilt. Therefor it had a brand new tranny and a virtually new motor put in at the exact same time. Now the crank has play in it once again.
 
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It’s the 3 speed auto I don’t know the part number of my tranny. I’m not sure, we sent the motor out didn’t even pull the oil pan
 
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