Holy cow..main crank shaft pully loose on my 4.0 engine

The 4.0 inline 6 engine in my '96 Cherokee has 188 k miles on it and (I thought) the serpentine belt or something close by has been squeaking badly for a month now. Tried all kinds of idler pulley tension adjustments and the squeaking continued. I go to start it today and the serp belt jumps right off. Turn the engine off, open the hood to find the belts off. I rotate the main belt driven cooling fan and the blades now nick the main crank case pulley. Started moving the main crank pulley and sure enough it tilts up and down a bit with hand movement and since it's hitting the fan blade I guess it's loosened up enough where it's migrated forward, away from the engine some.

I have zero experience dealing with this pulley but since there's plenty of clearance hopefully I can do what it takes to get it fixed.

Anybody have an idea of what's gone wrong or what part I need to replace?

Ir sounds like your talking about the harmonic balancer just replaced mine.

As jeep_ride says, you are at least looking for a new harmonic balancer. They aren't expensive. Probably about $50. I expect the old one will just come right off. The new one should need an installation tool in order to get it installed. They are supposed to be an interference fit. If the new one just slips right on then you are also looking at a problem with the crankshaft. Note that a mallet is not the proper installation tool. That technique can put you in the market for a new crankshaft.

I would plan on at least replacing the seal for the balancer while you are there. I can't imagine that seal is in particularly good shape after having a sloppy balancer flop around in it.

The harmonic balancer (aka pulley) is a two part piece, with the outer and inner sections separated by rubber. The rubber tends to dry rot and allow the outer piece to walk forward or backward and wobble.

Use a proper install tool or get a longer bolt and an extra washer and nut. Run the bolt all the way in, and turn the nut and washer to push the new balancer on. Do not try to use the original bolt to pull it on. It'll only grab a few threads at first, and you the risk ripping those threads out of the end of the crank.

The longer bolt is how I did mine worked like a charm you will need a harmonic Balancer puller puller to remove the balancer I think that's what its called I was able to remove the front bumper to gain better access to the balancer.

Thanks for all the advice. Looks like there's plenty of videos so this should be fairly straight forward.


Only problem is none of the vids went so far as to replace the front main seal. What's the deal is that a tough job or something?

When I have replaced the front seal I have done it with the timing cover removed. That makes it fairly easy to drive the seal out from the back side.

I don't know if you will want to remove the timing cover though. That opens up its own can of worms. The biggest concern is getting the timing cover back on, centered around the crank. Jeep left plenty of wiggle room for the timing cover and you are supposed to use a centering tool for the installation of it. The tool is not cheap, if you can even find it. Alternatively you can loosely install the timing cover, then install the harmonic balancer in order to center the timing cover, then remove the harmonic balancer so you can deal with the timing cover bolts that the HB covers up, then install the HB for the final time. Or, if you have access to lathe with a boring bar you can open up the ID of an old HB (one that was still in decent condition--I don't know if yours is or not) and use that as an install tool.

Other potential issues in that can of worms are the timing chain dampener (rubber block which will have hardened up like a rock and will probably want to be replaced) and the question of whether or not you should replace the chain itself while you are in there.

The other way to go is to use a seal puller to try to extract the seal. Problem is going to be the snout of the crank right in the middle of the area you want to be prying. And then there is the matter of driving in the new seal, again with the crank right in the way, and no way to support the back side of the timing cover while you pound in the new seal.

I can see why folks would avoid the job.

I pull the timing cover off and just plan to replace the chain and the chain dampener. And I have made my own centering tool, so that part of the job is no longer an issue for me.

My seal wasn't leaking so I didn’t bother it for all the above reasons.

s, need to check crankshaft movement. There is a possibility of bearings being damaged. I did have that happen a few years back on my '98 XJ. I replaced the crankshaft and the main bearings.
I did just replace the harmonic balancer on my '00 XJ. Sort of got burned once. They are $50. I did take off the front cover and replace the timing chain. The timing chain from NAPA was a bit better, but not much. I did a Cloyes on the '98. It was tight getting on. Also, a double roller. I did make up a plastic tool to center the front cover. There is also a rubber damper in there. Its about $8. Mine was hard and cracked.
I did find other stuff amiss. Still, check in and out of the crankshaft. It should only be a few thousands. On the '98 it was at least 1/8th.

My 1998's harmonic balancer lasted about 200,000 miles. No seals or timing chains needed useless diagnostics or leakage indicate otherwise