Hunter_

Hello, Im looking to replace the Very tired cam shaft in my 98 zj with the 4.0L, the problem I have is, I don't have a engine hoist, or any way to take the engine out. Is there any posable way to remove the almost 3 foot long cam shaft without taking the block off its mounts, also with it being flat tappet, would I have to pull the head and do lifters too?

dave1123

Yes, you have to pull the lifters out and the oil pump drive gear as well. Then pull the radiator and grill, jack the engine up, after pulling the motor mounts out, high enough for the camshaft to clear the front frame and bumper. You may need to disconnect the header pipe in order not to break it.

Bugout4x4

My curiosity would be if the cam is very tired, are the bearings also? If so it is a much bigger job.

Hunter_

Yeah, I'm a little worried about that myself. I figure if thats the case than rent a hoist and stand, and rebuild the thing.

dave1123

What makes you think the cam is shot? Because it rattles? That's normal for a 4.0. They are hydraulic lifters but there's no lash adjustment designed into the motor so once the rockers and pushrods wear a little, it makes noise. The only way to tell if the cam lobes are worn is to measure the lift or pull a lifter out and look at the lobe and the bottom of the lifter. My WJ has 225K miles on it and it rattles, but it runs strong. I know it could use a new chain and gears and maybe I'll get to that, but pull the cam? No way. It has 40 lbs of oil pressure idling hot and 55 on cold startup. It still has 85 psi compression minimum on all cylinders.

Hunter_

The 4.0's are notorious for having weak cams made from pore materials. Im certain that its not a rod knock, if it was push rods and rockers wouldn't it stabilize and stop rattling under higher engine speeds?

dave1123

I've never heard of soft cams in a 4.0. Yes, at highway speeds with high oil flow, it will quiet. You may have a cracked piston skirt. THAT is a known problem. You'd have to pull the pan and look for pieces to know for sure.

To know if it's the cam, you'd have to pull the head and lifters, inspect the lobes for rounding or gauling and see if the bottom of the lifters are cupped.

When we replaced my head, I looked at all the cam lobes and they were so nice I put a new set of lifters in it. It was quiet for a week, then started rattling again. I never measured the pushrod lengths or the rockers except to make sure the pushrod cups weren't cracked or the valve ends weren't worn with steps in them.

Bugout4x4

Unfortunately it is hard to tell until you get it all apart. But it will be much lighter to lift out. lol

Dave is right though... These things do have lifter rattle issues. And I am finding that for some reason they like to bend pushrods also. Have you pulled the cover and checked the pushrods yet?

Here's another thing I found about the rockers on these when I just rebuilt mine a few weeks ago. The rocker bridges somehow twist on their own under normal operation causing the rockers to become misaligned changing the geometry creating and more slack. I had to take a large pair of channel lock pliers and twist them all back into alignment to the valve stems with the pedestal bolts just snug then re-torque them. The pushrods were pushing them sideways instead of vertical. This cured my "Still rattling" issue on my new motor. It's quiet as a mouse now!

I'd try spinning the pushrods in a no pressure position to make sure they are straight, and take a look to see if the rockers are centered on the valve stems first.

Hunter_

I've not yet taken the head apart, I don't doubt that that they have rattle problems. this isn't my first 4.0, and I am aware of a lot of the quarks associated with it. This is what I've noticed, the engine is running rich witch throws an occasional code for the down wind O2 sensor, rattling in the block and during oil changes there is no fragmenting, and i've had the pan off, haven't spun a barring and the rods have no play in them. the rattling that the two of you are describing is vary common and more likely than not is harmless, it can be caused by a lack of oil, bent push rods and arms, and a warn camshaft. if my cam isn't knocking than what is, also if my cam was warn wouldn't that make it run lean?

dave1123

It sounds to me like a total teardown is about the only way to know for sure what's rattling. If it's knocking before oil pressure comes up after an oil change, that tells me it's bearings.

Bugout4x4

Man... While you had the pan off would have been the time to visually inspect the cam lobes and lifter bottoms to be sure. And check for piston skirt slack. But if you think the cam is knocking then you can bet it will also need bearings.

The rich condition could be several things aside from mechanical issues. Know what I suspect could be your knock? It very well could be your thrust bearing.

97grand4.0

After chasing a cold start rattle for some time I am concluding that with 200k I may well have a piston rattle. That being said it is only maybe slightly worse after 50k miles. I saw one post where a guy was able to demonstrate piston slap by poking a wood rod through the spark plug hole and rocking the piston at tdc. With the head off it is quite easy to check for any rocking at tdc. Also you can pull the pan, the easier method, and see from the bottom end if there is any rocking. There are a few good vids out there describing how to change just one piston and cure a piston that is actually broken skirt. If they are all worn, it becomes a question of 'now that I went this far...." and ...mains, rods, cam and bearings....and of course high mileage heads can have worn valves and guides....