As documented in an earlier article, I replaced my broken stock engine mounts with a set of Mountain Off-Road Enterprises (M.O.R.E.) BombProof mounts only ten months ago in February of 2000, so I was surprised to find that M.O.R.E. had just recently introduced a new design that specifically addresses the low-RPM noise issue that many Cherokee users of this product have noted. Even though I was perfectly happy with their older JM25840 mounts, the people at M.O.R.E. were gracious enough to send me a set of these new JM600 mounts to review. The installation procedure is basically unchanged from the first review excepting for the hassle of grinding the engine support fork to fit, so I will concentrate on the differences between the two models. Most of the pictures below have larger versions with detailed annotations, accessible by clicking on them.

   To the right is a picture of the JM600Z mounts fresh out of the box. The prefix 'Z' designates that they have been zinc plated for corrosion resistance. They also offer painted and unpainted versions. Upon inspecting the damping material, it is immediately obvious that it is much softer than that used on the JM25840, which uses a very stiff polyurethane that I initially mistook for Delrin, a plastic material.
   Despite the necessity to remove the oil filter mount to access the passenger side mount, there is a fairly generous amount of room to work around it. The driver side mount is a completely different story, however. Not only is it difficult to photograph, there being no particularly good angle that illustrates the mounting scheme clearly, it very cumbersome to actually work on. The picture on the left is the driver side, hidden under the intake manifold and air tube. The photo on the left shows a well-muddied passenger mount.

   I removed the old JM25840 pair per the previously documented procedure, and cleaned them thoroughly to see if they showed any sign of deterioration over the last ten months. In this time period, I had repeatedly landed the Jeep hard enough to punch ?" holes all the way through the sheet metal in the wheel wheels with the anti-sway bar linkages, but there were no apparent signs of this abuse anywhere in the mounts, inside or out. All of the mold lines in polyurethane bushings looked as good as the day they showed up on my doorstep. This is a good indication of how incompliant they are, and thus their ability to transmit vibration.
   In the side-by-side comparison photo to the right, it is clear that the large mass of soft material will provide a much higher degree of damping than the hard delrin. However, it looks as if the people at M.O.R.E. did not compromise the toughness of this product in any way, as the damping material is completely enclosed in a thick steel cage, ensuring that it will not fail in the same way as the stock mounts, which are more or less unconstrained blocks of rubber.
   One step in the original instructions that looks like it might be easy to skip is really not. Before, the driver side engine support fork had to be removed so that it could be ground to clear the flanges of the polyurethane bushings. However, it is still much easier to remove the fork along with the motor mount, swap out the mount, loosely attach the assembly with a few threads on each screw, and then tighten them all down after the engine settles into the proper position. With the fork hard-mounted, it is extremely difficult to align the motor so that the mount lines up with its respective holes.
   The diagram that the left photo is linked to shows the interference points that had to be mitigated on the fork. The material that had to be removed from the fork is highlighted in the right link. Obviously, this is procedure is something that is better avoided, and it is clear from the picture of the new installation that no such modification is necessary to fit stock vehicles.

   So the mount seems plenty tough, and plenty easy to install especially in contrast to the older design, but the big question is whether or not it does a better job filtering out engine vibration. That they have decided to completely enclose the rubber suggests that this will not be as plush as the stock mount, and it is not. However, it is very significantly smoother than the JM25840 mounts, which I only really had problems with at idle. What has completely disappeared is the rattling humdrum from every loose screw and clip in my well-beaten Jeep being excited while the engine was idling, and the bus-like feeling on the freeway that I had mentioned before. Given the abuse that this thing is made to endure, it is unrealistic to believe that it could be as soft as the stock mount, and remarkable that they are as smooth as they are. I am much happier with these installed.

You can contact M.O.R.E at:
P.O. Box 843
Rifle, Colorado 81650
(970) 625-0500
www.mountainoffroad.com