HappyTrails

Actually, only half of that is correct. I did shear off the right side motor mount bracket bolts at the engine block. But not getting air at Pismo. I was in a parking lot of a fruit stand and merely started the engine. BAM. The whole thing fell over on the right side, jamming the motor mount and bracket where it was a total PITA to get out. Reading up on this later, some busted off the distributor. Others put the fan through the radiator. Some had the drive line come up through the floor. I guess I was lucky to only have a broken fan shroud.

The bracket is held on with three bolts. Only two would came out with extractors. Third one was abandoned and we modified the bracket with an extension tab to take up the next block hole back. The one with the wire clamp. Rear drive line had to be disconnected and the radiator fan and both motor mounts removed for the engine to lower enough to get these engine block bolt holes below the frame for doing the repair. Be sure to use proper ramps, lifts and jacks so you don't drop that 4.0L battleship anchor on yourself when doing this job.

Plenty written up on this issue. Check it out if interested. Factory defect in bolts seating at end of holes before fully seating against the bracket. Vibration fatigue from a very slightly loose bracket eventually causes the bolts to fail. One was gone a long time ago. But I never new it until I saw the grease filled hole with the broken bolt it in.

Check your bolts! Can't see 'em from on top. Get it up on ramps and work between the frame and bracket to replace them one at a time with 1.25 inch 3/8 course thread grade 8. Use two washers and you should be good.

Can you imagine having this problem on the back side of Bumstuck Mountain somewhere? I just glad it was near where I could get help and get it repaired!

Firestorm500

Hmmmm. I was at Pismo back in November, and I didn't shear off any motor mount bolts.

I didn't stop at any fruit stands, though.

cruiser54

With which Jeep?

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.



Maybe you should do some noggin pokin, eh?

Firestorm500

Cruiser54: "With which Jeep?"

I had my '92 Laredo there.

cruiser54

Can't nail down the year range with this motor mount bracket issue. Seems like 95 to 96 is pretty common.

muffinman

Mine is a 1995. Mine DID shear off on the back of Bumstuck Mountain! Check those bolts boys.

cruiser54

You fall into the year range.....

Firestorm500

Well when I replaced the engine in the '92 about 14,000 miles ago, I also replaced the motor mounts. The rubber was looking dry rotted, at least on the surface.

Much easier to change them while the engine's out. No mention was made of fluky bolts.

HappyTrails

The bolts in question are the three that hold the bracket to the block. Not the two that hold the mount to the chassis. Be sure to replace them. They do not normally have to come out just to replace the motor mounts and can easily be overlooked. Not a hard task, but a little tight on the passenger side. But hopefully when you got your new engine these bracket bolts were replaced when the mount brackets were installed.

HappyTrails

Mine is an "early" 96 with the hand painted letters below the spark plugs. From what I understand, these came out of the engine factory before the major retooling in 96. The issue could be clue how badly the tooling "dun got wore out" by that time. So inaccurately drilled holes would be no surprise.

BTW, on the midnight fix we were only able to extract the front broken bolt. The other two were impossible in the dirt in the dark. I drove another 80 miles with the engine hanging on that one front bolt!!! YIKES!!!

The next day I fabbed a strut that ran from the bottom of the rear outer AC compressor bolt hole to the frame flange below and behind the alternator. Ran bolts through both ends of the strut. Made it home the day following. 178 miles. No problems. Took it right to the shop here. $550 and 3 days later I have it all back right. New mounts included.

Firestorm500

Happy Trails: I would imagine the installer put the original bolts back in. I hope '92's were stronger than later years.