primegreen

Thought I'd put this here as a little tip for anyone else who's been chasing this problem without finding the solution. I've had this for about 6 months and have read post after post about it. One of the things I didn't see mentioned but ended up being the cause for me was the ENGINE BRACKET bolts. NOT the motor mounts, but the bracket that motor mount connects to. One of my bolts on the passenger side bracket was broken off inside the block. Once I put new brown dog mounts in, there was more rigidity in the driveline and it exposed the flaw. Got under the jeep and looked around and sure enough one of the 3 bolts that holds the bracket in was shorn clean off. I got the brown dog super brackets (8 bolts hold it in instead of the stock 3) and problem solved.

Thought I'd post this tip. If just one person reads this and checks their bracket bolts and finds one or more broken, I'd have saved a 4.0!

cruiser54

To follow up:

From Jon Kelley aka 5-90 @ www.kelleyswip.com



This is a known issue.

1) Unless you're going to get silly with the skinny pedal, 2xSAE8 screws on one side won't be a huge problem. You'd be better off with three, but if you don't get silly you'll be okeh.

2) The Brown Dog engine mounts use two or three additional holes on each side, and spread the mount/clamping force over more of the block. This is invariably a good idea, and I'll probably be doing it as I refit my 88.

3) The primary reason that the screws snap is because, sometimes, the screw holes in the block aren't drilled & tapped deeply enough. This causes the screw to bottom out in the hole, so you end up torquing against the bottom of the hole instead of stretching the screw (as you're supposed to do. Not your fault - you aren't doing anything wrong.) The screw is not stretched properly, and the head is not butted up against the bracket, so there's some room to move there. Vibration then causes wear cycles on the screw, which generally leads to rupture.

The easy/cheap fix? When you replace the screws (3/8"-16x1.25", as I recall,) put two flat washers under the head before you screw it into the hole.

The check? Take a feeler gage (.003" to .005") and try to slide it under the head of the screw. You'll be able to get under the corners (look at the hex head, and you'll see that the surfaces curve toward each other slightly) if it's a standard hex head - if it's a flanged hex head, you should not be able to get under the head anywhere. If you can slip the gage under the head, you have a problem. If you can touch the shank of the screw, you have a big problem!

In no case should you reuse the screws after you take them out - they'll be stressed under the head, and you'll have a significant reduction in strength. Replace them outright, putting washers under the head as I mentioned before. The washers will make up for the slight lack of depth in the hole (two of them will be about 0.125" or so,) and allow the screw to be preloaded properly.

LadyKenai

interesting tip

is this a certain year only or for all 4.0's ?

cause there is a clunk in my 88 xj and cant seem to find it and only does it in the wintertime

cruiser54

I doubt that's your issue because once they come loose, they don't ever get better.

But, this issue began with the HO blocks. Never hurts to poke your noggin under there and look anyway.

When those break it's a big repair.

LadyKenai

i will certainly do that, ive already replaced the motor mounts i should of peeked a ltitle deeper, thanks seems a small effort to prevent a big repair indeed.

marc