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M.O.R.E. Motor Mounts

Source: Jeep at Off-Road.com
M.O.R.E. Motor Mounts
By Steve Chang & Chris Geiger

The need to swap out the motor mounts in my 1990 Cherokee XJ 4.0L was not immediately obvious to me. With 135,000 miles on the odometer and a decent amount of moderate off-road use, strange noises from the Jeep are fairly common, but one sound had me particularly worried. A reasonably audible thunk-thunk-thunk noise, apparently from the front, was evident every morning when I started my Jeep, most times when I was making a hard left turn or pulling away in first gear, and occasionally even when parked with the engine at idle.

I suspected that this sound was coming from either some loose suspension parts or some part of the drivetrain thunking against the underside of the vehicle. I had recently changed out the clutch by myself, and it was quite possible that I had reinstalled the transmission/transfer case assembly improperly. However, when I had someone else start the Jeep while I listened and watched the drivetrain from underneath, the rest of the engine noises masked the elusive thump while it could still be heard clearly in the cabin, and there was no visible knocking of parts. My installation of the 3” Skyjacker lift was removed from the list of suspects when I re-tightened all of the suspension and steering components to no avail.

Finally, I watched the engine mounts while the engine was turned over, but there seemed to be nothing remarkable occurring with either one of them, so it came down to the process of replacing parts until the noise went away. The decision to start with the engine mounts was based solely on cost. Of course, I had to go find a beefy aftermarket replacement for it instead of buying the wimpy OEM parts.

I had heard that Mountain Off-Road Enterprises (M.O.R.E.) and Rusty’s Offroad made these parts for the XJ. I looked at their respective web sites, and formed the opinion that M.O.R.E., with an entire line of burly-looking BombProof™ engine mounts for various Jeeps, should have a better handle on the design of these products than Rusty’s, which advertised only the XJ mount. However, I should note that the two products are extremely similar in appearance and price.

Upon initial inspection of the installation of the factory mounts, it becomes immediately obvious that the oil filter mount has to be detached from the engine block for the passenger’s side engine mount pivot bolt to be removed. Also, access to the top screw of the driver’s side mount requires that the flexible air tube that spans the air box and the intake manifold be moved out of the way. Other than these two issues and the fact that the factory service manual lists no torque specifications for these parts, the job seemed fairly straightforward. These are the steps that I took:

1. Grease the new engine mount bushings. 2. Drain oil and remove oil filter. While unnecessary to the installation of the engine mounts, it seemed to me that unless this was done, the next step would be exceptionally messy

3. Remove oil filter mount by unscrewing a hex bolt immediately below and outboard to the oil filter sealing surface. This was messy enough even with the oil drained and the oil filter removed. Had I been more thoughtful, I would have put a funnel and a drain plan directly underneath the parts to capture the predictable ensuing oil spill. Upon inspection of the three o-ring seals on this part, I noticed that they were extremely flat and brittle, obviously in dire need of replacement.

I was able to find the two smaller o-rings shown in the picture at a local parts store easily, but no store in town had the largest one in stock. I was forced to leave this o-ring in the assembly. There are no leaks yet, but I will replace it at the next oil change.

4. Remove the two nuts that fasten the passenger side engine mount to the frame. One is accessible from the top and the other from underneath the engine. A set of extensions that, when connected together, total about two feet is extremely helpful in removing the bottom nut. I have a set of wobble extensions that allow the socket axis to be somewhat misaligned with the driver axis of rotation, without taking up all of the space of a universal joint.

5. Raise the engine off of the frame by jacking on the oil pan with a floor jack cushioned with a block of wood. The passenger side engine mount should just barely be loose from the frame.

6. Remove the engine mount pivot bolt and nut holding the engine mount to its fork and replace the old engine mount with the new mount. The rubber part of the old mount, as indicated in the picture, was torn about halfway through, obviously at the end of its useful life.

7. Assemble the new engine mount to the fork with the engine mount pivot bolt. Getting the fork and mount holes to line up required me to lift the engine a little more and yank it around a bit while pushing on the bolt until it slid through.

8. Spin the motor mount-to-frame attachment nuts onto their respective studs a few threads down. Leaving these nuts loose, while still capturing the engine mount in this way will ease the alignment of the whole engine assembly with the new mounts to the frame.

9. Lower the engine back down so that the jack is no longer supporting any of its weight. 10. Loosen the hose clamp that holds the flexible intake air tube to the air box, and move the air tube to open up a direct access line to the engine mount-to-frame bolt.

11. Remove the nut and bolt that fasten the driver side engine mount to the frame. As with the passenger side mount, one is accessible from the top and the other from underneath the engine. The wobble extensions are very helpful here, since the position of the intake manifold makes it very difficult to get straight at the bolt head.

12. Raise the engine off of the frame by jacking on the oil pan with a floor jack cushioned with a block of wood. The driver side engine mount should just barely be loose from the frame.

13. Remove the engine mount pivot bolt and nut holding the engine mount to its fork. The engine mount should now be free.

14. Remove the old engine mount. As the picture clearly illustrates, the steel sleeve has completely torn away from the bulk of the rubber isolator. This mount is obviously way past the end of its useful life.

15. Position the new engine mount in the stock location. If it doesn’t seat all the way down to the frame, modifications to the fork and/or the new engine mount will be necessary. This problem is noted as a possible issue in the installation instructions, though I was hoping that this would not be the case for my vehicle and the installation would go smoothly. How often does that happen?!

16. Remove the fork by unscrewing the three bolts that attach it to the engine block. Here, the short wobble extension was basically essential since the frame pad for the engine mount severely restricted access to the most forward bolt head. As is evident in the picture, the interference between the delrin bushing and the fork results in a very significant hole misalignment. I felt uncomfortable about removing this much material from the fork, but the amount of delrin that had to be trimmed would not allow the bushing to fully seat on entire circumference of the steel tubing.

I compromised by trimming enough delrin to leave just enough of a lip on the bushing to fully seat on the steel tubing, and grinding the fork enough to make it fit. The picture shows how little grinding is actually necessary when done this way.

17. After reattaching the fork to the engine block, you’re basically home free. Position the new engine mount in the stock location, reinstall the engine mount pivot bolt, spin the engine mount-to-frame attachment bolts on a few threads, and lower the engine onto the engine mounts.

18. With everything sitting happy, tighten the engine mount-to-frame bolts.

19. Reinstall the air tube. 20. Reinstall the oil filter mount and oil filter. Remember to fill the engine back up with oil. 21. Since the engine will sit higher with these stiffer mounts, it’s a good idea to lower the hood slowly to make sure nothing is going to hit.


 
 
 
 
 
 
 
 
Starting up the Jeep was a whole new experience. All the engine starting sounds that I heard while underneath the engine were now clearly audible inside the cabin, though the problem thunk-thunk-thunk was finally gone!.

At idle, the vibration and noise are much more prominent, but I was given plenty of warning in advance by the guy who took my order at M.O.R.E. that this would be the case, so there were no surprises in this department. While driving around town or on the freeway, there is a somewhat noticeable increase in noise, though I tuned it out, along with the rest of the noises that my decade-old vehicle makes, within a couple dozen miles.

Also, when hard on the accelerator, the 4.0L sounds like a cross between a racecar and a bus. I’m guessing that the mount would probably afford a higher degree of vibration and sound isolation without compromising strength if it used a preloaded polyurethane bushing instead of the hard delrin part. Overall, I’m very happy with the product, given that I’ll probably never have to replace my motor mounts again.

 

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