Block Side Motor Mounts

[Weasel]

Passenger side sheared off like as happened with many others. I have a new engine going in and considering making new mounts that would grab a couple extra bolt holes, question is if it's worth it? Do the stock mounts fail because of the bolt size or because they loosen up? I have some high strength 3/8 bolts I am going to be using and if it's an issue of them loosening they can go in with Red loctite. It's easier to build the mount with the engine out but still have to build them. I am not buying them, too much money for what they are.

 

[Jump This]

A lot of the Jeepspeed guys use the extra threaded holes in the block to build larger mounts. Although loose bolts will cause failure, just the abuse
we dish out will tear up a stock mount.
Talk to the Jeepspeed guys here, they will be able to point you in the right direction.

 

[JeepFreak21]

Were the bolts that sheered grade 5, grade 8, or what?
Billy

 

[Weasel]

Stock bolts, so whatever they are. If I pick up two extra 3/8 holes I can add almost 50% more shear strength then the stock setup. For the drivers side it would be too hard to get two as there are a couple along the top of the oil pan. Passenger side is a bit tighter and maybe harder to pick up the bolts.

 

[slcpunk74]

anybody have a link to pitch and length of those bolts just so if anyone would want to buy some to replace the stockers?

 

[Weasel]

3/8-16 1" long

 

[Boostwerks.com]

I've been curious about this...Is it typical for the bolts to fail in shear or do they rip out of the iron block? If the bolts simply fail in shear, some higher grade hardware and a "torque damper" should fix the problem. If it's the actual block that fails, the larger mount would be the best way to go.

 

[JeepFreak21]

Here's some good discussion on the topic for you...
http://www.naxja.org/forum/showthread.php?p=243728371&highlight=sheer#post243728371
Billy

 

[Weasel]

Hey thanks for the link, forgot about it. Think I'm just going to add some extra bracing on the stock mounts and pick up a few extra bolts.

 

[5-90]

They typically fail in shear because they bottom out in the holes (thus failing to achieve tensile preload.)

The usual fix if you catch it before it breaks is simple - one or two flat washers on the affected screw(s).

 

[Weasel]

They typically fail in shear because they bottom out in the holes (thus failing to achieve tensile preload.)

The usual fix if you catch it before it breaks is simple - one or two flat washers on the affected screw(s).

Not sure where this comes from. The stock bolts are a tad over 1" and do not bottom out, I've checked the depth of the holes, thickness of the brackets and everything is good. New bolts are exactly at 1" and are not close to bottoming. :dunno:

 

[5-90]

Hm. Just what I'd heard - and it does make sense (the mode of failure, that is.)

I've not had it happen to me yet, so I can't FA it and see for myself what's going on...

 

[Weasel]

I suspect it's due to loosening. Dealer said it's a common failure on Forest Service XJ's which tend to be older models, high miles and lots of vibrations.

I'll check the bolts when I pull the engine but so far it didn't look like a simple shear overload.

 

[WrenchMonkey]

Mine broke off six months ago:

http://www.naxja.org/forum/showthread.php?t=970843

The extra bolts are a good idea, but I wouldn't run the loctite.

That might keep em from breaking, but if it doesn't, you're going to have one hell of a time getting the broken stubs out of the block...

Two cents, a week late...

Robert

 

[Tom_T&Js_Offroad]

we make brackets for the xj. pm me for details