Motor mount bolts broke in block..
#1
Thread Starter
Junior Member
Joined: Jul 2015
Posts: 40
Likes: 0
From: British Columbia, Canada
Year: 1995
Model: Cherokee
Engine: 4.0L l6 HO
Motor mount bolts broke in block..
Only a few hours ago was I out on a mountain exploring when I suddenly heard horrible noises from my front end. To spare you the time reading my silly story, it wast my engine sagging down causing my fan to try and rip apart the shroud. Now I am stuck with three bolts in my engine block. At least the view was good. I don't have any experience with this kind of thing but I know I will be able to fix it with some help, such as methods and tips from some other unfortunate person who has had the same luck.
Here are some pictures
It seems to me that two of the holes are dirty and and rusty possibly implying that only one bolt was holding everything together when it broke. Suggestions on tools and such would be appreciated.
Here are some pictures
It seems to me that two of the holes are dirty and and rusty possibly implying that only one bolt was holding everything together when it broke. Suggestions on tools and such would be appreciated.
#2
Senior Member
Joined: Mar 2014
Posts: 952
Likes: 55
From: Eastern Long Island, NY
Year: 1996
Model: Cherokee
Engine: I6 Cyl / 4L
https://www.cherokeeforum.com/f2/bro...removal-32757/
https://www.cherokeeforum.com/f2/hel...red-off-85910/
There are more threads that cover this if you want to keep searching
Good luck.
https://www.cherokeeforum.com/f2/hel...red-off-85910/
There are more threads that cover this if you want to keep searching
Good luck.
#3
Thread Starter
Junior Member
Joined: Jul 2015
Posts: 40
Likes: 0
From: British Columbia, Canada
Year: 1995
Model: Cherokee
Engine: 4.0L l6 HO
https://www.cherokeeforum.com/f2/bro...removal-32757/
https://www.cherokeeforum.com/f2/hel...red-off-85910/
There are more threads that cover this if you want to keep searching
Good luck.
https://www.cherokeeforum.com/f2/hel...red-off-85910/
There are more threads that cover this if you want to keep searching
Good luck.
#4
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,566
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Here's why:
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.
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