Crank seal replace - 90 Cherokee

Yup, the leak from the valve cover that is pretending to be a rear crank seal leak....

These engines are tilted back and the valve covers tend to leak. This runs right down a grove in the back and drips off the bell housing bottom or oil pan.

To test, run the engine for a bit, then take a clean rag and wipe the head below the valve cover. If you come up with oil, then I recommend you change this gasket before worrying about the bottom.

If the bottom does need fixing, the pan comes off fairly easy, the starter might be in the way.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

jbcrow wrote:

Replacing that seal is an easy job, but it is probably not necessary. The WAY more common ailment that gives a symptom similar to that is the Valve Cover Gasket. The VCG typically breaks somewhere towards the rear of the motor, and the oil flows out and down the back of the block, into the bell housing, and down to the inspection plate that covers the flywheel or torque converter. It LOOKS for all the world like the rear main has taken a dump, but it is really the VCG.

One other note, this is the real oil seal and I plan on doing this with the engine in the vehicle. Am I overly optimistic about this not being too bad of a job?

thanks again, JB

It's at most a two banana job, opposable thumbs are not required. The only difficulty I ran into was getting the upper seal out. Kind of baked in. There was a steel core in the seal and I used a brass drift on that and

*carefully* tapped the seal out. While you have the pan off it's not a bad idea to take a peek at the bearings. Jeff '00 XJ, '91YJ

Biggest problems I had doing it that way were:

1. getting the pan off. The original gasket had fused into the block and pan - almost like a weld. That lead to 2.

1. cleaning off the old gasket. Only way I can puit it was "What a bitch"!

2. getting the top half of the seal out. Mine was grown in about like the pan gasket. Get a length of brass rod just less than 1/4 inch diameter to use as a driver so that you don't score the crank. I pounded a good half inch mushroom on the end of the one I used before that half seal finally broke loose. I had loosened all the main caps and let the tranny droop just enough to take the pressure off but it still took a BMFH and some serious pounding to get that thing out. That was the worst one I ever tried to do and I've done a few. The new one slipped in slick as snot. (Don't forget to lift the tranny back up and re-torque the mains ).

Simple job, but the devil's in the details. Getting the old pan gasket off is a royal pain but be sure it's all off and clean. I used the 3-piece pan gasket set and that's fun to keep in place but I under stand that there is a one piece gasket available that would simplify things a bit.

It is a relatively easy, but time consuming job in that the oil pan has to be removed. I had to take one motor mount loose and jack the block a little. You want to be very careful when putting the new one is so as not to damage it.

Every time someone mentions replacing the rear main seal here, you get several comments about the valve cover being your actual problem. Obviously they have never seen a rear seal leak, but it is as common as the valve cover in the 4.2 and the 4.0 after say, 80K miles, and very easy to distinguish the difference.

That said, as they say, its easy to check for a leaking valve cover gasket.

It is easy to do it with the motor in place. But, you should REALLY take a look at the Valve Cover Gasket first.

Most of us here that comment that the Valve Cover Gasket is the real problem replaced the rear main first, and still had an oil leak. Some of us thought the persistant leak was due to inadvertantly getting the oil pan gasket on wrong, and aftger fixing that, still had a leak. After parking on a hill and physically watching the oil flow out of the valve cover was the first clue that the main seal was not the problem. We are only sharing the experience in hoping that our brother in Jeeping can benefit from that experience.

In 30+ years of driving and over a dozen cars/trucks, I have never seen a rear main seal go bad. I understand that I live a particularly protected life, but the only time I actually considered the rear main seal, my trouble was the valve cover gasket. Maybe it's just me, but I detect a pattern here.

Once I thought it was my rear main seal because i had sucha big leak and the back of the head was clean. It ended up being a bad oil pan gasket at the back. I hit the pan earlier and deformed the gasket surface. While I was in changing the pan gasket, I figured what the heck do the main seal. The very hardest part of the rear main seal job is removing the factory paper gasket material from the block. It took me 6 hours of hard labor lol. KH

Hi CRWLR,

I am only sharing experience also.

A couple of years ago I had a severe oil leak and also posted here for help. And rightly so, it was recommended that I check the VCG. I tried to explain to the group that, what was coming from the top of the motor was not nearly the amount that was coming out of the bell housing. As I posted earlier, to me, it was easy to distinguish the difference. But I changed the VCG anyway because it was easier, but the drip... drip... drip, still persisted. After changing the RMS, the problem was solved. I now can actually change my oil rather than just feed it through.

Fairly common enough:

All I am saying is, check the VCG but don't rule out the RMS... it's easy to tell the difference:

JimG

If the engine is oily enough that you can't readily determine where the leak is, and since the rocker cover gasket is so easy to do, I'd start at the top and work down. The gasket isn't that expensive and it never hurts to renew it, even if it's not the source of the leak.

-- Old Crow '82 Shovelhead FLT 92" 'Pearl' '95 Jeep YJ Rio Grande ASE Certified Master Auto Tech + L1 TOMKAT, BS#133, SENS, MAMBM, DOF#51

I prefer the Ultra- black to the blue as it looks more professional and I think seals better. Also I use brake cleaner spray, because I have unlimited access to it. Color me cheap.

-- Old Crow '82 Shovelhead FLT 92" 'Pearl' '95 Jeep YJ Rio Grande ASE Certified Master Auto Tech + L1 TOMKAT, BS#133, SENS, MAMBM, DOF#51

I want to first thank everyone for all the help. I took your advice and checked out and replaced the VCG. Unfortunately there was no change. On to the rear crank seal. Only problem now is getting the oil pan out. It was a bear getting the pan separated but with some work it came apart. Took off 2 nuts for the motor mount, but the engine doesn't want to move without taking the body with it. Am I missing something? Do I need to remove the mounts on both sides? Will be back at it tommorow.

Thanks again, JB

I used a bottle jack between the axle and the block. On my 4.2 there is 3 bolts into the block and 2 on the mount. Make sure it's free.

And to the VCG guys... yes, sometimes it IS the RMS (or something other than the VCG).

-- JimG

80' CJ-7 258 CID 35" BFG MT on 15x10 Centerlines D44 Rear, Dana 30 Front. SOA 4.56 Gears, LockRight F&R Dana 300 w/4:1 & Currie twin sticks Warn X8000i w/ dual batteries

I was able to work mine out by removing the starter and raising the rear of the engine (unbolt the tranny mount and raise it with the transmission. It still took some twisting and wiggling. Funny thing is, it always seemed to slide back in with no problem - it was only stubborn coming out. I think the starter has to come loose in any event and I had the jack stands under the frame so that the front axle dropped quite a bit. I doubt it would have cleared the axle with weight on it if the stands were under the axle.