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The 4.0L Jeep’s Weak Link

Posted in How To on March 1, 2001
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Photographers: John Cappa
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Drive your Jeep onto level ground, block the tires, put the parking brake on, and put the tranny in Neutral. Grab your floor jack and a block of wood and roll it under your oil pan. Put the block of wood between your oil pan and the jack and raise the jack and wood apparatus just enough to take the engine’s weight off of the motor mounts. (It’s a good idea to have a block of wood about the same size as the bottom of your oil pan to displace the weight evenly.) Drive your Jeep onto level ground, block the tires, put the parking brake on, and put the tranny in Neutral. Grab your floor jack and a block of wood and roll it under your oil pan. Put the block of wood between your oil pan and the jack and raise the jack and wood apparatus just enough to take the engine’s weight off of the motor mounts. (It’s a good idea to have a block of wood about the same size as the bottom of your oil pan to displace the weight evenly.)
Remember to only do one motor mount at a time, starting with the driver side. We found that removing the airbox made the swap a lot easier. You may want someone else to raise or lower the engine until the cross-bolt is loose and can slide out easily. When removing the cross-bolts, pay attention to which way they are facing, since you’ll want to reinstall them the same way as the factory did. Remove the retaining bolt on top and then the nut from the underside of the old motor mount. Hold on to the nuts and bolts because you will need them to reinstall the new unit. Remember to only do one motor mount at a time, starting with the driver side. We found that removing the airbox made the swap a lot easier. You may want someone else to raise or lower the engine until the cross-bolt is loose and can slide out easily. When removing the cross-bolts, pay attention to which way they are facing, since you’ll want to reinstall them the same way as the factory did. Remove the retaining bolt on top and then the nut from the underside of the old motor mount. Hold on to the nuts and bolts because you will need them to reinstall the new unit.
You may want to check the cross-bolt clearance before installation in your Jeep. Tight tolerances and bolt variation could be troublesome when trying to realign the motor on the new mounts. You may want to check the cross-bolt clearance before installation in your Jeep. Tight tolerances and bolt variation could be troublesome when trying to realign the motor on the new mounts.
Air tools can keep you from tossing chairs like Bobby Knight after a lousy game. A breaker bar can also work wonders on these stubborn cross-bolts. Air tools can keep you from tossing chairs like Bobby Knight after a lousy game. A breaker bar can also work wonders on these stubborn cross-bolts.
Once you pull out the old motor mount, compare it to the M.O.R.E. piece and you’ll know why you need the new ones. Now bolt up the new mount, but leave the nuts and bolts finger-tight until you are done with the other side. Again, having another person work the jack up or down to align the bolt holes can save you lots of time and frustration. Note the nifty little cracks on the low-mileage OEM piece we took out (arrow). Once you pull out the old motor mount, compare it to the M.O.R.E. piece and you’ll know why you need the new ones. Now bolt up the new mount, but leave the nuts and bolts finger-tight until you are done with the other side. Again, having another person work the jack up or down to align the bolt holes can save you lots of time and frustration. Note the nifty little cracks on the low-mileage OEM piece we took out (arrow).
The installation is the same for the passenger side (although there is a lot more stuff in your way) unless you have an older Cherokee. If you do have an older-model XJ, you may need to change your oil at the same time as swapping motor mounts. This is because the older-style XJ oil filter housings will need to be removed from the block to access the motor mount retaining bolts. Don’t worry, the oil filter housing is sealed with rubber washers, so just clean everything up before you put it back together—no new gaskets required. The installation is the same for the passenger side (although there is a lot more stuff in your way) unless you have an older Cherokee. If you do have an older-model XJ, you may need to change your oil at the same time as swapping motor mounts. This is because the older-style XJ oil filter housings will need to be removed from the block to access the motor mount retaining bolts. Don’t worry, the oil filter housing is sealed with rubber washers, so just clean everything up before you put it back together—no new gaskets required.
Once you get both the new mounts in place, torque everything to factory specs. After removing the jack and wooden block, reinstall the airbox. Once you get both the new mounts in place, torque everything to factory specs. After removing the jack and wooden block, reinstall the airbox.
These M.O.R.E. motor mounts are much more resistant to flex and—most importantly—damn near impossible to break on the trail. Cherokee owners should expect a little extra vibration after installing these motor mounts, but not nearly as much as the polyurethane units. Besides a little extra vibration is par for the course if you need the extra insurance of bombproof motor mounts. These M.O.R.E. motor mounts are much more resistant to flex and—most importantly—damn near impossible to break on the trail. Cherokee owners should expect a little extra vibration after installing these motor mounts, but not nearly as much as the polyurethane units. Besides a little extra vibration is par for the course if you need the extra insurance of bombproof motor mounts.

The 4.0L Jeep engines have a bit of a weak link in their easily worn-out factory motor mounts. If you drive your 4.0L like a grandma on sedatives you probably won’t experience this problem. But if you suddenly get inspired by the last rerun of The Dukes of Hazzard and try to jump over a patrol car, or blast down a dry riverbed filled with rocks the size of Flash the dog, you probably will experience at least one broken motor mount.

All kidding aside, with hard street starts, trailer towing, and almost any type of off-roading, the OEM motor mounts will start to disintegrate. As with any component on your Jeep, the motor mounts are susceptible to damage from the elements, especially when you think about the amount of motor oil, road grime, ATF, and so on, that has probably come in contact with your motor mounts over the years. Factor in that barely balanced yet torquey straight-six, and you will quickly see small cracks developing in the factory rubber bushings. These cracks mean the cross-bolt holding up your motor can shift around more. Next thing you know, the sheetmetal-like motor mount has given way, and your 4.0L is leaning to its side like George Jones after a rough night.

For a few years now, bombproof motor mounts made with polyurethane bushings for the 4.0L have been available as aftermarket parts. While these units have proven to be more than adequate for Wranglers, Cherokee owners have not had this option. The polyurethane mounts will fit Cherokees quite easily, but the vibrations that result from this swap-in to a unibody frame are unbearable. Since chipped teeth and the factory mounts are both unacceptable to the folks at M.O.R.E., they decided to find a solution for these nasty vibrations and came up with some rubber-bushing bombproof motor mounts just for Cherokees.

These trick mounts bring down the vibrations to barely noticeable levels, so watch and learn while Mo Weitzel from Off Road General Store installs a set of these babies in a ’97 Cherokee.

Sources

Off Road General Store
Laguna Hills, CA 92653
www.offroadgs.com

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