So, my oil pressure would be fine when cold then would drop to 0 on idle when warm. I did all the usual, changed the sensor... twice... and added a mechanical gauge. Both read 0 at operating temp at idle.

There was a split second rattle on cold start that worried me, but it was not consistent. Sometimes it would rattle others it wouldn't. It pushed me more towards a tear down.

I also pulled the oil pan, and saw what 230,000km with probably only 10 oil changes looked like.. there was 1/2" of sludge, carbon and general corruption in the bottom and coating the entire pan. I pulled the valve cover, and it was the same. It looked like black carbon crystals growing all over everything.

Out the motor came, and the teardown began.

I found that the cam its self was warn so bad that the bearing surfaces looked like dark gray granite. Some of the lobes have minor wear but the cam has gotta go anyways because of the bearing surfaces. The bearings themselvs looked the same.

The main bearings show wear, as do the rod bearings. The crank mains and lobes all show the same wear, so it needs a polishing. And new bearings all around.

The cylinders all look fine with no scratches, the pistons are the same. No cracks and the wrist pins are all tight in their bores. Piston #6 had a ring broken in 3 places .. so all new rings too. Of course a honing and good washing is in order too.

The block, and crank is going to the machine shop for a dip and to have cam bearings installed. I'm going to have them check the mains for alignment and concentricity / ovality.

So.. when it all gets back I will measure ID's and OD's, calculate and order what I need... This is fun... I hope... REALLY hope... That this fixes my problem and brings some youthfulness to my XJ

Does anyone have suggestions for cam upgrades?

Thanks for reading.

 

Yeah, it's saveable. Personally, I'd start with a .010" grind on all the crank and rod bearings and a .010" overbore on the cylinders. Stick with a stock cam for longevity. Just my opinion.

 

I am with Dave on this. Basically take it all down fresh and true and a new stock cam. It is probably going to feel like a powerhouse compared to how it ran before. And the best thing about a freshened up engine is you can do everything right from the very beginning

 

I'm taking it into my shop for a run threw the cleaner a few times. And I have spoken to the local machine shop. It's about $500 for a cleaning, cam bearings re&re, and crank grind. I'll need a new cam unless they can take it down too. Can I get under sized cam bearings? Is it even worth it?

 

No, you can't grind the cam bearings undersized anymore than you can grind the lobe profile, especially on the 4.0 because if you reduce the overall valve geometry, there's no adjustment in the rockers to take up the slack. Many years ago, there were companies that would take a stock cam and regrind the profile to make it a "3/4 race" cam, whatever that meant. By regrinding the base circle, you can effectively increase the lift, but most of them were junk. They also require adjustable rockers. Remember also those lobes have to fit thru the bearings to install it, so you can't regrind the bearings smaller than the lobes. On most engines the bearings get a little smaller the farther you go back from the front to make it easier to install the cam so each one is a different diameter. If you buy a cam bearing set, they are numbered so you get them right when you install them. I've installed cam bearings myself.

The camshaft is the breathing heart of an engine. It's profile is what makes an engine perform the way it's designed to. The opening ramp, closing ramp, lift, and duration control what kind of power and torque you get out of it. The jeep 4.0L engine is designed as a low rpm, high torque engine. Just what we need for slogging thru the mud!

BTW, it cost me $300 to get my head reconditioned. A new Clearwater head cost me $455 complete with new valves, springs and seals. They have gone up in price since I bought mine.