Lifters?

Do 4.0's have roller lifters?

No ...

Do you think my lifters or cam could be wornout with 170,000 miles. It runs fine but i am lind of looking for an excuse to get a bigger cam.

Sure, they could be, if the oil wasn't changed very regularly.

On the other hand, my '88 XJ is at 247,000+ miles and I don't think the cam and lifters are worn out. Worn, sure, but not worn out.

If you want a cam ... buy a cam. Just remember that dropping a new cam into a 170,000 mile engine is asking to blow up the engine. If you want to go with a more powerful cam, you really need to "freshen up" the engine at the same time you do the cam.

Eagle said:

Sure, they could be, if the oil wasn't changed very regularly.

On the other hand, my '88 XJ is at 247,000+ miles and I don't think the cam and lifters are worn out. Worn, sure, but not worn out.

If you want a cam ... buy a cam. Just remember that dropping a new cam into a 170,000 mile engine is asking to blow up the engine. If you want to go with a more powerful cam, you really need to "freshen up" the engine at the same time you do the cam.

Click to expand...

Yeah, i bought it with 135,000 miles on it, but i think the guy took really good care of it. Every time I change the oil it comes out pretty clean, so im guessing the oil was changed regularly. I figure since poeple are getting 200,000 miles+ out of these things easily, why not just put the cam in. I guess having a cam might acelerate bearing wear, sinse it makes more power, but could it wear them out that much faster?

It's not so much the bearings. The bearings will only see more pressure when you actually USE the extra power the cam can produce. Driving down the road at 60 MPH uses the same horsepower regardless of what cam you have in it.

IMHO the problem is that when you get on it, you'll be producing more cylnder pressure and putting more stress on 170,000 mile rings and valves. Also, your cam bearings are 170,000 miles old and are nicely worn in to mate with the existing camshaft. Now you want to throw in a new camshaft, but you probably aren't set up to pull the old cam bearings and press in new ones with the engine inthe vehicle.

You can do it and it'll run for awhile, but I would not expect that engine to be a 300,000 mile engine.

I see what your saying. If I do put a cam in, I'll put an oil pump and cam bearings in it too, and a timing chain while I'm at it.

Do 4.0's have any common high mileage related problems? (oil pump, timing chain, lifters)

91 4.0XJ said:

Do 4.0's have any common high mileage related problems? (oil pump, timing chain, lifters)

Click to expand...

Some folks have replaced the rod bearings (rods only, not mains) and found them worn down to the copper backing. If the oil is changed regularly this should not be a problem. If you have abnormally low oil pressure, that's where to start.

Timing chain? I replaced my timing chain a couple of years ago, at around 210,000 miles or so (don't remember exactly), not because I was having any problems but because I was over 200,000 miles and I remembered that AMC V8s used nylon teeth on the cam sprocket. When they got old, the teeth would break off, the engine would jump time, and things went rapidly downhill from there.

So changing the timing chain was a pre-emptive strike. Except ... when I got in there I found that the cam sprocket was NOT nylon, the teeth were steel. The chain was not a flat style, it was a single roller style (original -- I bought the XJ new in 1988), and there was NO perceptible slack. I already had the new chain and sprockets, so I went ahead with the replacement ... but I kept the old parts and I would not hesitate to put them into a beater that needed a timing chain.

In general, unless you mistreat them badly, these are 250k to 300k engines.

Thanks for the info. I beleive that my jeep was taken pretty good care of, so i think it might be capable of 250,000-300,000 miles. That would be something to brag about to other people who think only diesels can run that long.

speaking of 300,000+ miles on a engine I just ran into a 91 xj with 375,000+ on it and the origonal owner said it has never been rebuilt. He still drives it daily. by the way it is for sale since hes retiring