Ok I'm a newb to the jeep scene. I see a lot of people talking of changing their motor mounts. Is this a common problem on an Xj or is their a benefit to changing them?

 

X2 been wondering the same thing

 

Motor mounts go bad over time and can have many adverse effects on other parts of the jeep. Cracked manifold is one of the possible side effects of bad engine mounts. It is definitely something that needs to be monitored to ensure everything runs like it should.

Something like this is not holding the engine like its supposed to...

 

^This, the engine mounts are a poor design and are prone to failure (all rubber engine mounts fail eventually, but the Jeep 4.0L ones fail earlier than most), and cheap aftermarket replacements are even worse (the first replacement engine mount I put on my XJ was a cheap "Anchor" brand one that lasted less than a year). Luckily the engine mounts are easy to replace, it only takes about 1/2 hr. per side (throw a jack with a 2X4 scrap to spread out the weight under the oil pan to support the engine, than it is just 3 bolts each, removing the air-box, etc. makes it easier though).


If you really want good/long lasting mounts and don't mind a little extra vibration you can go with Brown-Dogs or other similar "heavy-duty" aftermarket mounts (a metal mount with a round rubber/poly bushing, rather then the OE "rubber blocks") which while a little expensive (about $100/pair) will likely never need to be replaced again.
http://browndogindustries.com/CU2572...ts-Rubber.aspx
http://browndogindustries.com/C2572-...unts-Poly.aspx

 

Thanks for the info guys

 

Forget the brown dogs and get the o.e.m mounts or whatever brand advance/autozone etc. The brown dogs have a ton of extra vibration. Horrible with the ac on.

 

The 4.0 is big and kinda heavy which is hell on motor mounts and you throw in vibrations mounts won't last that long,And even driving habits can wear them out faster if you drive it hard.

 

I got bad motor mounts, so does my parts jeep and so did my xj. so yes a common issue change them as soon as ya can.

 

http://www.ironman4x4fab.com/Products/MM.html


Anybody use these guys?

 

I replaced mine with Brown Dog!!! Then I read the instructions and followed the process of adjusting them and NO more vibrations at all. Most everyone over tightens the big bolt --- but if you back it off you can adjust the vibration out!!!!

 

I'm running Brown Dog rubber mounts and have zero vibes. Took about 500-600miles for them to break in good.. At first yes there was a slight and I mean slight vibe, but now its great.. The through bolt is not torque specific most ppl over tighten them and get mad vibes. I'm glad I went BD motor mounts.
Here is a vid from my dash cam stuck to windshield with cheap mount(picks up every little pump or vibe).. You can read the lic on the car.. You can see if there was a bad vibe the vid would show it.. Looks smooth on vid and feels good and solid.

 

If left to long this can happen to the block, not good the bolt for the motor is what broke the block. But can be repaired use the Brown Dog motor mount setup that uses 6 holes for mounting instead of 3.

 

That's a long red-light...lol

 

no issues here. torqued properly, and broken in. I can cruise around town, the highway, the mountain with AC on full bore, no vibes.

 

Just to be clear for the uninitiated, what he's referring to here with that horrifying pic is a known flaw in the way the engine mounting brackets were installed in some years. The holes in the block for the mounting brackets (that connect the engine to the engine mounts) were too shallow, so that when they installed the bolts to hold them in place, they were torqued down against the bottom of the hole instead of against the mounting bracket. That left the mounting bracket slightly loose, and over time the vibrations can cause damage and failure. Worn motor mounts can contribute to the problem. Usually it's just the bolt that breaks, causing the engine to tilt so that the mechanical fan digs into the radiator. Not all years had the issue.

In addition to their motor mounts, Brown Dog also sells a set of replacement engine brackets that are thicker, so that the bolts torque against the bracket instead of the bottom of the hole. The original brackets only used four holes on one side and three on the other. The BD replacements use additional holes in the block that were tapped at the factory but never used, seven on one side and eight on the other. If you install these brackets with their motor mounts, your engine is definitely going to stay where you put it no matter what kind of abuse you put to your Jeep.

Here's a pic of their "Super Kit" with the brackets and motor mounts:



Regarding the motor mounts themselves, BD offers a polyurethane version and a hard rubber version. The poly version is harder and would naturally transmit more vibration, but the rubber version isn't exactly soft. One good thing about this design is that although it's made to last a very long time, if you ever needed to replace them you would only need to replace the insert bushings. And even if the bushing is worn out, you can bang those suckers all around and never lose the mount completely because the main mounting bolt is trapped in the steel tube.

I have the full BD kit with rubber bushings that I installed with my stroker. At first it vibrated like a massage chair, but it has calmed down considerably after breaking in. I really don't understand the whining about the vibrations. It's a frickin' Jeep, not a Range Rover.