What else should I do while I have it opened up? 4.0 Jeep engine content.

1996 ZJ, 4.0/AT/4×4, 270k miles, original and unmolested. Runs way better than any Chrysler product has a right to at this age and mileage.

The engine oil leaks have gone from nuisance condition to needs service ASAP status. The main culprit is the oil pan gasket. The valve cover gasket and oil filter adapter housing are also leaking. I can tell if the rear main is leaking or not, if it is, it's not a big leak.

So it seems that dropping the pan to do the gasket with the engine in place isn't that hard, some recommend doing the rear main seal whether it's leaking or not, and at this milage, I've got to think that changing out the oil pump is the wise choice. The pump does seems to have acceptable pressure now, 40psi on cold oil, 20/30 psi on hot oil, according to the gauge on the dash.

I don't want to touch the harmonic balancer, and the front seal doesn't look like it leaks, but if I loosen the bearing caps to gain access to the rear seal, is it likely that the front will be damaged in the process?

What else should I do, or at least inspect, while I'm in the pan? I'll also be pulling the VC, any known trouble areas up there?

Skip the cork valve cover gasket, stick with the Fel Pro rubber/steel gasket, and don't forget the washers/seals for the bolts too.

I know you don't want to pull the harmonic dampener, but at that mileage a timing chain might not be a bad, while your at it, idea.

Other wise, source a 4.2l crank and rods, Edlebrock makes a Performer series head. Comp or Hesco will hook you up with the cam, springs, push rods, and roller rockers.

We should first be asking, what are your goals for the motor?

If you just want to keep driving the thing:
if the rear main isn't leaking don't change it. not familiar with jeep rear mains, but I feel like every time I do a rear main I do it twice to get it right. Not fun. Maybe that's just me.

Fix what is leaking, keep driving.

In reply to Robbie:

Its our family DD right now. I will replace it as a DD in the near future, but we will be keeping it as a camping/dog/dirt bike hauler. It's cost per mile and usefulness have been to good to dump it.

So no modifications are being considered, but I'd like to make any repairs right and once.

Do the rear main seal while the oil pan is off. If the oil pump pickup screen is clean, I wouldn't bother with the oil pump. Avoid any cork gaskets, stick with the Felpro R series rubber gaskets.

What Lee said, stroker build time .

And it doesn't run like a Chrysler product because it isn't, it's an AMC (sort of.) As an aside, I find it somewhat hilarious the combined efforts of Chrysler and AMC, with a bit of Renault and Puegeot thrown in for good measure, were able to yield a product as renowned for its reliability as the XJ is.

Front main is a cakewalk compared to the rear, if you're already in that deep.
Give the pan and pickup screen a good cleaning, and a new timing chain. Wouldn't touch much else on the bottom end. Same with anything in the head.

At that mileage anything more than gaskets will be opening up big wear locations. If oil pressure is good, leave the pump alone. If oil pressure is bad a new pump usually won't fix the problem anyway, those pumps never fail. Don't touch the bearings if you aren't willing to pull the whole engine.

Maybe send the injectors out for cleaning. But on those AMC sixes, it's generally the ancillaries and frame that go before the engine.

In reply to hhaase:

Don't I need to loosen all the main bearing caps, and remove the rearmost cap to do the rear main? Or are you talking about the rod end bearings?

Rear main seal I was under the impression you were planning to do. Personally I wouldn't touch it unless its real bad for exactly that reason, gotta pull bearing caps. Front main iirc is on the timing cover and just pops off.

Your that f into the car, water pump for sure on top of other suggestions.

Probably new freeze plugs, but for the most notorious leaking one you'll have to pull the engine as IIRC it's at the back of the engine.

I think pretty much all old american iron rear mains have a slow drip, some of them probably dripped when new. I'd leave it be and just do what you mentioned along with a timing chain and associated seals/gaskets, it's almost certainly stretched to an unacceptable degree and will run better with a fresh one.

wearymicrobe wrote: Your that f into the car, water pump for sure on top of other suggestions.

Water pump isn't bad at all to get at. Leave well enough alone unless it needs to be replaced.

Ok, so I just read a couple of write ups on Jeep forums about rear main seal replacement. None mentioned loosening all the other bearing caps, does this sound right?

BTW, the WP is only about a year old, and it looks like it's possible to pull the timing chain cover with the WP in place, which would be nice because I'd rather not drain the coolant if I don't need to.

Only the rear main cap has to be removed to do the rear main seal, do it while the pan is off or you'll still have a leak.

Do it all- parts are cheap and you are already in there! I did both front and rear main seals, oil pump, timing chain/gears, and the harmonic balancer. I started like you, looking to seal the leaks. Had to do the pan gasket twice, everything else was straight forward. Did I mention XJ parts are really cheap?

Rear main is a cake walk. It's a two-piece seal. Drop the pan, drop the rear bearing cap, push the upper-half out.
The lip on the seal is the pressure side, on the other side of the seal there will be a notch that runs the circumfrance of the seal.
1 - Put a LITTLE bit of RTV in that groove.
2 - Work the upper seal into the block easy, slow and easy, keeping the sealing surface against the crank journal to prevent the block from cutting the seal.
3 - Get the seal flush with the block, more or less. The seal will be just a little proud of the block on either side of the crank.
4 - Put the lower half of the seal in the cap.
5 - Torquify the cap.
6 - Put a little RTV in the seams in the block (two on the front cover, two at the rear).
7 - Use RTV sparingly as glue to keep the pan gasket in place.

*Note, you might have to unbolt the front shocks to let the axle drop an extra 2" to get the pan out. Sometimes I had to do that, sometimes I didn't.

I think that's it. I've done hundreds of these, they really are simple. My fastest time was 45 minutes (in the shop). In my driveway I can knock one out in 2 hours.
I'll second the fact that the oil pump is typically fine for 350K miles.