aa7kn

I have the 4.0 in my XJ, 1991 model. the rear main seal was leaking so I had it replaced. stopped leaking for a week or so and started leaking again. took it to my mechanic and when he pulled it apart again, the journal where the seal rides against on the crank was marked up pretty bad with some sort of a pattern. he said this is not good and that is why the seal is being eaten up by the rough spots on the crank. he said the crank needs to be removed and sent to the machine shop to turn this area so it is totally smooth and round, then the seal will seat and no more leaks will happen. is this correct ? I guess I am asking for your opinions on this, as the spot on the crank where the seal goes/rides looks like it was made this way. can someone confirm that this seal journal should be smooth and shinny silver and not gold colored and have a marks pattern on it ? thank you very much.

md21722

Seals need to ride on a smooth clean surface or they will leak. If the crank has a groove in it from riding on an old seal then your mechanic is right. If you can feel it with your finger dragging over the area, then your crank needs to be machined.

'90Cherokee

The mechanic should have seen that the first time around and notified you that there was a problem with the crank. Sounds like he might be making excuses for doing a poor job or even covering up that he damaged the crank when replacing the seal.

aa7kn

yes |agree that he should have seen it the first time. thanks for the input guys, i already knew that the seals need a smooth clean surface to ride against but I just needed reassurance....thanks again and one more question....IF the seal journal is machined down to a smooth pretty surface, can you or do I need to install an over sized seal ? kind of like the bearings ? I never heard of an over size seal...thanks

dans98xj

from the design of the seal it should be fine. they usually have a lip on them that rides on the crank. there should be enough play in that to still seal. At the most the machine shop will only take off a couple thousandths to ensure a smooth surface.

DFlintstone

This whole business sounds funky to me. How long did you have it before the leak? "the crank was marked up pretty bad with some sort of a pattern" Huh? I haven't done a 4.0, but I read getting the top half of the seal out without marring the crank can be a challenge. If it is new to you maybe someone before marred/mucked it. If not, likely is was that shop...Btw, often the guy screwing up your car is not the guy you deal with up front. (he might not even know what happened)

Also be aware with the common oil filter adapter O ring leak, that oil blows back and mimics a leaking RM. I need to change my RM, probably because someone messed it up because of the O rings leaking. I fixed the rings, and now need to go at the RM.

'90Cherokee

Did you see this pattern or did he tell you about it. If you saw it can you describe it? I can't imagine any way for it to happen on it's own. Replacing the upper seal half can be difficult and he may have scratched the crank, but it wouldn't be a pattern all the way around unless he did something really strange. Removing mine took some pretty aggressive hammering with a punch, I can easily imagine someone with less care doing damage.

Did he put it back together, if so, is it still leaking? Verify that the valve cover gasket and oil filter aren't leaking, most leaks will run to the rear and look like a RMS seal leak. Even if there's some wear on the crank it might not be the cause of the leak. I did my RMS, it was original and completely toast. A few days later it's leaking again, but less than before. I discovered the valve cover had loosened.

The seal lip is pretty well compressed so I don't think machining a small amount off the crank would keep the seal from working.

cherokee37

I'm sorry I was talking more of the bump stop itself

aa7kn

well all is fixed now, turns out the guy at the jeep dealer some how put the seal in backwards, the top half went into the block ok but somehow he got the bottom half backwards...they changed it and let a different mechanic see it and fix it, all is ok now, the pattern and ribbing on the crank was caused buy the design of the seal and that it was in wrong, they took some smooth emery cloth and smoothed out the crank, installed the new seal and so far...no more leaking....just wanted to put some closure to this one.....thanks guys for all the in put.

'90Cherokee

I see no way that a seal installed backwards would put any marks on the crank. I also don't see taking some emery cloth to the crank being a proper repair for a person who damaged the crank. I would actually be more pissed about someone doing this, unless they removed the crank first. If you're satisfied that's fine, I'd be up their ***.

Rustic D.

not sure about the crank but i have had good success with handy shims on front seals. fix's that high mileage groove cut by the seal. my rear main on my 87 4.0 is leaking pretty good, so im going to be in your shoes soon. looks like a very thin pipe coupling which slides over the crank end or harmonic balancer, leaving you a nice smooth surface for a new seal. Bought thru napa.

'90Cherokee

Can't be done on the rear since there's no way to slide one on. My rear seal was so old it had turned to stone, pulled it off in little pieces, no grove luckily.

Rustic D.

Had not considered the flange on the back of the crank. no way to use a handy shim there. Gotta do my rear main seal asap, turned some high r's and its leaking bad!! First time to remove tranny and t-case in 20 years of service. Bet my seal will be petrafied also. Bought my 87 in 97, great x.j.

'90Cherokee

No reason to remove the trans., can't get it from there. It's a two piece seal and it's serviced by removing the oil pan, then the rear crank bearing cap.

Rustic D.

Thanx for the tip, had no idea it was done from the pan. Got lots to do, bunch of renix electrical restore and this rear main seal. Cruiser54 sent many links to fixing some age old electrical issues on this 87! Thanks 90cherokee for your help.