cavalier
NAXJA Forum User
- Location
- Detroit, MI
Are most XJs passenger side?
-
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What side Engine Mount Bracket Bolts Did You Break?
- Thread starter cavalier
- Start date
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
No. Read this:
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.
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.
- Location
- Hammertown, USA
I don't know how much weight I put behind that article. I have a hard time believing its a consistent quality problem spanning 19 years and 5 factories, not managing to tap bolt holes correctly.
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
It didn't span all those years.
As far as I know, there weren't 5 engine factories that made the 4.0.
And, I saw this personally as a Service Manager at a Jeep dealership in the first HOs.
As far as I know, there weren't 5 engine factories that made the 4.0.
And, I saw this personally as a Service Manager at a Jeep dealership in the first HOs.
- Location
- Hammertown, USA
The problem did span 87 to 06.
The 4.0 was used in 5 different vehicles.
The Cherokee alone had 4 separate block castings for the 4.0.
Maybe the engine wasn't made in 5 factories, maybe it was. My statement holds equally if not more valid with these stats than the very general stating above.
The 4.0 was used in 5 different vehicles.
The Cherokee alone had 4 separate block castings for the 4.0.
Maybe the engine wasn't made in 5 factories, maybe it was. My statement holds equally if not more valid with these stats than the very general stating above.
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
I'm lost here. We never had this problem at the dealership until the HOs first came out. I know it continued through 1992. I left the dealership then.
- Location
- Hammertown, USA
You may not have had this problem in the potentially 5 years you worked on fairly new 4.0's, but its been a problem many people have had in the 13 years since.
"I didnt see it, so it doesnt exist."
One of stinkyfab's biggest customers is jeep dealerships buying his plates as a repair for stock TJ's with broken off motor mount boss's.
"I didnt see it, so it doesnt exist."
One of stinkyfab's biggest customers is jeep dealerships buying his plates as a repair for stock TJ's with broken off motor mount boss's.
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
So it continued after the early HOs?
- Location
- Hammertown, USA
Yes. There were several block revisions but none of them really seemed to help the problem.
I've never seen another engine with such a common block failure, and I have no idea what causes it.
I've never seen another engine with such a common block failure, and I have no idea what causes it.
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
- Location
- Hammertown, USA
i don't buy that as the problem
8Mud
NAXJA Forum User
- Location
- Central Germany
Some kind of screwup going on, they actually offered two different bolt lengths for the same application in the Renix years. One offering was 1.12" and the other was 1.00".
Then in the Chrysler years the same bolts were made out of a different material, I know for a fact the Renix bolts are a lot harder then the Chrysler bolts. I drilled out a couple on my 96, they weren't all that hard to drill.
So in a nutshell two different problems with basically the same results, broken bolts.
It's also possible Chrysler they put those bolts in there with a predesigned shear factor, to break before the cast iron on the block broke and/or the bolts pulled the threads out. I went to Chrysler truck school and we had some hours on the predesigned weak points, the parts designed to fail first to act as a kind of fuse to save more expensive parts, like U-Joints before axles or axle splines.
All in all a poor design, at least one more bolt would have likely been advisable. I imagine the bean counters and the engineers had some discussions about this.
old_man
NAXJA Forum User
- Location
- Loveland, Colorado
In case someone doubts this, I have personally seen this on several engines, including mine. The first thing I do when I pull a mount is to grind down the end of the bolt just a bit. The washer idea is good also.