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Snapped Engine Mount Bolts

Old 10-01-2015, 03:26 AM
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Default Snapped Engine Mount Bolts

So I was driving home today, about 2 minutes from home and heard what sounded like a large rock hit under the drivers seat (RHD) so got home and started.

The Jeep:
'95 Cherokee Limited, RHD - Australian, 4WD (Full Time Option), D30HP, D35 LSD 3.55

So I checked for any visible damage to the gearbox or sump as thats where I thought the sound was coming from but nothing, so I started it and the pressures were fine.

So I got my wife to start it when she got home while i was under it to see if I could hear the area the noise was coming from but nothing, so I grabbed a glass of wine (yeah I know, not the typical drink for a jeep owner but each to their own) and stood back and looked, then I noticed this





So I tried to join the hose but it was too short so I stood back, had a drink and then thought "well the engine has moved", so I checked the mounts on that side and it was fine.

Then I checked the drivers side (or passenger side for those who drive on the wrong side of the road - right side) and well this is what I found









Hmm looks like I will be having fun this week end.
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Old 10-01-2015, 05:58 AM
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Angle drill bits and easy out. The factory bolts bottom out b4 getting tight use shorter bolts when reataching..
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Old 10-01-2015, 08:22 AM
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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.
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Old 10-01-2015, 09:22 AM
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Default Thanks Cruiser

Just went out and checked mine and they are ready to be replaced ASAP. I can actually see a little "Shiny" behind one of them.


Your experience is greatly appreciated!
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Old 10-01-2015, 09:29 AM
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Wow that's nuts! Sorry to see that man.

Aren't there normally 3 bolts holding the motor mount bracket to the block? Or did earlier engines only have 2?
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Old 10-01-2015, 02:28 PM
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Originally Posted by freegdr View Post
Angle drill bits and easy out. The factory bolts bottom out b4 getting tight use shorter bolts when reataching..
Thats basically the plan I don't think there will be the space for an angle drill so I'm going to undo the other mount and lower the engine so there is clearance to get at the bolts

Originally Posted by cruiser54 View Post
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.
I brought the vehicle about 3 months ago and to be honest didn't even think about checking the engine mount bolts, i checked the mounts from the top but that was it.

It appears the outside 2 bolts have been snapped for a while and then the middle 1 failed which is to be expected.

Unless you were doing the bolts up with a rattle gun you would feel the issue cause a bottoming out bolt feels different to a tight bolt but hey, I knew there'd be something to need doing on a 20 year old jeep.

Thanks for the bolt spec info, I was going to ask for that
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Old 10-01-2015, 02:43 PM
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Originally Posted by Bugout4x4 View Post
Just went out and checked mine and they are ready to be replaced ASAP. I can actually see a little "Shiny" behind one of them.


Your experience is greatly appreciated!
Woohoo!!! Glad you found it now.
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Old 10-01-2015, 02:51 PM
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Originally Posted by Bugout4x4 View Post
Just went out and checked mine and they are ready to be replaced ASAP. I can actually see a little "Shiny" behind one of them.

Your experience is greatly appreciated!
I'll take a few snaps as I go, and post. Hopefully it'll help

Originally Posted by t.mcginley.jr View Post
Wow that's nuts! Sorry to see that man.

Aren't there normally 3 bolts holding the motor mount bracket to the block? Or did earlier engines only have 2?
There are 3, its just that 2 have been snapped for a while buy the colour of them, they are not clean so they have been exposed to the elements for a while.
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Old 10-01-2015, 03:00 PM
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Originally Posted by Freakn View Post
Thats basically the plan I don't think there will be the space for an angle drill so I'm going to undo the other mount and lower the engine so there is clearance to get at the bolts



I brought the vehicle about 3 months ago and to be honest didn't even think about checking the engine mount bolts, i checked the mounts from the top but that was it.

It appears the outside 2 bolts have been snapped for a while and then the middle 1 failed which is to be expected.

Unless you were doing the bolts up with a rattle gun you would feel the issue cause a bottoming out bolt feels different to a tight bolt but hey, I knew there'd be something to need doing on a 20 year old jeep.

Thanks for the bolt spec info, I was going to ask for that
Small angle drill will work.I had to shorten the drill bit. We removed the dist so motor would drop further could only get two out but better than pulling motor. Got any harbour freight close 2 ya heres what we used. http://www.harborfreight.com/38-in-V...ill-60610.html

Last edited by freegdr; 10-01-2015 at 03:05 PM.
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Old 10-01-2015, 07:11 PM
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Default Same happened to me...NOT easy to fix in the field.

Went through this a year or so ago. Cruiser54's info is essential to pay attention to EVERYONE!!!. Fix yours now, before you get stuck somewhere and have to just pull the plates and vin tag, set it on fire, and hike out! This is not an easy field fix.
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Old 10-02-2015, 02:10 AM
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Well I've picked up supplies for tomorrow

Jack Stands
Battery Operated Rattle Gun
Rigid Screw Extractors
New Bolts
Tap set
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Old 10-02-2015, 02:12 AM
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Originally Posted by Freakn View Post
Well I've picked up supplies for tomorrow

Jack Stands
Battery Operated Rattle Gun
Rigid Screw Extractors
New Bolts
Tap set
Good luck...
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Old 10-02-2015, 02:56 AM
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I would of gone the angle drill option but the only ones i could find were $200 plus

Power tools in Australia are way over priced

Thanks
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Old 10-02-2015, 03:18 AM
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Originally Posted by Freakn View Post
I would of gone the angle drill option but the only ones i could find were $200 plus

Power tools in Australia are way over priced

Thanks
Understood didnt catch the Australia untill now.
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Old 10-02-2015, 03:32 AM
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Funny part is I've seen harbour freight enough on this site so knew who they were and I wish I had one close
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