99-01 Bad motor mount boss' on block?

I just read a few recent 4x4 mags, and there are references to the 99-01 Cherokee 4.0 have bad blocks? Aparently the motor mount boss' are weak and can rip from the block rendering the block ruined. I've never heard of this, any of you??

Angus

Angus said:

I just read a few recent 4x4 mags, and there are references to the 99-01 Cherokee 4.0 have bad blocks? Aparently the motor mount boss' are weak and can rip from the block rendering the block ruined. I've never heard of this, any of you??

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Never heard of this. If it is true, I'd also expect it to affect TJs since they used the same castings. Do they have any references to back this up?

I'm sure you are referring to the contributions tothe latest rags.

It's not a problem specific to late model 4.0's, or XJ's.

If your Jeep sees any air-time, the bosses can break. Otherwise, it's not a problem.

It is common on some. My 95 has broken them 3 times in the 11 years ive owned it and I do not see any air time. It does not ruin the block, it just breaks the studs off at the block. Its a real PIA to get them out, but its doable. It now has grade 8 bolts and lock washers instead of studs and has been holding quite well. These will be my next purchase.http://www.mountainoffroad.com/more.htm

jeepme said:

It is common on some. My 95 has broken them 3 times in the 11 years ive owned it and I do not see any air time. It does not ruin the block, it just breaks the studs off at the block. Its a real PIA to get them out, but its doable. It now has grade 8 bolts and lock washers instead of studs and has been holding quite well. These will be my next purchase.http://www.mountainoffroad.com/more.htm

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It will break the bosses when you step up to good bolts. Better to stay with grade 8's.......a nice fuse.

Apparently, there are also some issues where the bolts might "bottom out" in the holes. Over time, or with a severe shock or two, this can result in the bolts snapping off nearly flush with the block surface, making them a HUGE pain to get out!

Solution? Add a couple washers, make sure the bolt head bottoms on the washers (rather than the shank bottoming in the hole,) and torque. Should be fine.

Given that a "fuze" is being recommended, I'd consider using SAE Grade 5 or CRES bolts, rather than SAE Grade 8. Both are not heat-treated to as hard a temper, and are therefore not as strong. However, they are plenty strong for motor mount brackets - and you can save the SAE Grade 8 for replacing the through bolt (although I'd probably use a modified AN/NAS bolt, so I could get a full-size shank through the mount. Threads loaded in shear generally aren't good...)

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