Motor Mount bracket bolts sheared off in block

Well I got a chance to look at the broken motor mount that we encountered over the Holiday weekend at URE...

Not a broken motor mount at all, but all 3 bolts are sheared off in the block on the passenger side..

Anyone ever encountered this PIA?

It is not uncommon. As it turns out the holes in the block are a bit too shallow and the bolts bottom out, allowing the bracket to flex, leading to failure.

You should be able to drill and use an easyout to remove the bolts from the block. Several companies make replacement brackets that use additional bolt holes. These work but are pricey. Personally I would remove the bolts then replace them with ones that are a hair shorter and make sure they snug up without bottoming out.

What about some washers on the bolts once I get the broken threads out?

SavedDad said:

What about some washers on the bolts once I get the broken threads out?

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I've seen that work. Either way, use some Locktite. Being a machinist, I prefer to grind down the bolts to where they do not bottom.

I have seen people run bolts in the holes that were too long and break the casting.

I did my 96 not long ago. It was a pain. I didn't try to cut any corners and opened up the area as far as possible, removed the battery, battery tray and A/C line hold downs. Unbolted the motor mount from the frame (bottom), easier to remove the whole mount than the cross bolt IMO. I used a block of wood on the pan rim (bolt tops) and used a jack to jack the passengers side as high as practical.

I got lucky, two of the bolt stubs were fairly loose in the threads after applying penetrating oil. The third I let soak overnight. All three stubs came out without much issue.

I Had a close quarter angle drill. My son showed up with some short Cobalt drill bits. Cobalt drill bits make drilling hardened bolts a lot easier.

A couple of tips, you may be able to rent an angle drill. Makita right angle drill (DA3010F) is the narrowest available (we found). Makita was the only one we found that was narrow enough to fit. Be careful with Easy Outs, don't try too much pressure, even the good ones can snap off and make the job a whole lot harder.

A million dollar trick for rusted in bolts or brake lines. Heat, then quench with spray oil, repeat half a dozen times. Expand and contract to help break the bond and at the same time help the oil penetrate as far down the threads as possible. It doesn't take all that much heat, a propane torch or even a heat gun will do it.

I have a set of left handed drill bits for just this reason. Most times as you drill the remaining bolt will thread itself out at some point.

I too have a 96. No motor mount problems yet, but with my luck....

Is it just the passenger side that tends to break bolts?

Runnin'OnEmpty said:

I too have a 96. No motor mount problems yet, but with my luck....

Is it just the passenger side that tends to break bolts?

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Something you can do is a close visual inspection. A small mirror and a good flashlight, some contortions over and under and you can eventually see all the bolts. It's likely one or two may snap before they all go (eventually)

Mine looked like the bottom bolt snapped first, one or both of the top bolts were cracked or weakened. My son bounced the XJ off a rock, didn't do any damage except that was the nudge it took for the other two bolts to snap off. I got lucky, no fan, radiator or other damage. I didn't have a fan shroud, I can imagine with the shroud on it could have made a heck of a racket and done more damage.

My drivers side bolts were good. The last time I did the exhaust manifold I checked the drivers side bolts, all were good. No stretching to cracks that I could detect.

I installed some early Renix motor mount bolts (used) I had in the shop. Slightly different design and a tad shorter than the 96 bolts.

Runnin'OnEmpty said:

I too have a 96. No motor mount problems yet, but with my luck....

Is it just the passenger side that tends to break bolts?

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If I were you, I would remove the bolts one by one and at least add washers.
Both sides.

Happened on my '88. Rt side all sheared off and engine dropped. I bought a small rt angle drill attachment to drill them out. I already had some excellent Blue Point straight flute easy outs. Got them all out.

Make sure you get the right bolts including their hardness. Change out the other side while you're at it.

Does this happen thru all the years or did jeep finally figure it out?

Heavyopp said:

Does this happen thru all the years or did jeep finally figure it out?

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Never happened on my 87 or 88 (I beat the snot out of my 88 ), happened on my (wifes) 96. Noticed the Renix bolts were a little different and a tad shorter on my Renix. I measured them with a dial gauge. Best guess is the mounts are a little under engineered on all models. And when they changed the bolts on the HO's it wasn't an improvement and they were a little too long.

I've never compared the early bolts and late bolts, new unused, for length. I've wondered if the length issue could be stretching? Or more likely some engineer made a mistake. The early bolts seem to hold up better. but the whole motor mount fastening at the top is still a little weak IMO.

I've had numerous bolts out of the block at the top of the motor mounts on the Renix, never noticed any issues, reused them all.