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Unread 08-15-2008, 11:11 PM   #1
BrunoS
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WARNING: All 4.0 owners check your motor mount/block Bolts!!!!

WARNING: All 4.0 owners check your motor mount/block Bolts!!!!

Grab a socket and check all the motor mount bolts that go into the engine block of your 4.0!!!! if any are loose, replace them now as odds are if ANY are loose then you have a stress crack in those that are NOT loose now! When the remaining bolts fail...you will be stuck with several sheared bolts in the engine block at best or cracked mounting bosses on the block.

Simply put....the right front (passenger) side motor mount/bolts that secure the lower mount mount to the engine block can vibrate loose a hair. This loads up the remaining two bolts, and they will start to stress crack. Then, on a normal highway drive without much load, go over a small bump and POP....The lower mount will then shear off the three grade #5 bolts that go into the engine block.

when this happens...the shifter will move 3 inches to the right, and you will hear the main cooling fan hitting the radiator shroud.....get off the gas, shut the motor down. you will save your radiator, a/c hard lines, and a bunch of other stuff.

To fix...my shop did everything but was only to get one bolt out. They replaced it with a new bolt, and heliarc welded the lower motor mount to the engine block bosses in two spots to prevent any movement or vibration from getting the plate loose ever again. If i ever pull the block, it can be machined off during the rebuild and the bolts removed.

i understand that a company is selling 'bomb proof motor mounts' for around $240 or so that utilize the 7 or 8 bolt studs available on that side of the motor. having seen what happened on mine...i hope i have saved everyone some trouble.

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Unread 08-16-2008, 12:49 PM   #2
jeepjack1995
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ive been there and it sucked.
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Unread 08-16-2008, 02:16 PM   #3
MudColoredXJ
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Yep, happened on my 95 a few years back pulling out of the driveway. I basically had to unbolt all drivetrane mounting bolts and drop the motor/tranny/x-fer case as one unit. This enabled me to get a drill bit square on the sheared off bolts by going through the wheel wells. Got two out and replaced. The third was a lost casue. I also had to put a helicoil in one of the holes. Quite possibly the worst experience yet with my jeep.
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Unread 08-16-2008, 02:44 PM   #4
mattathayde
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Quote:
Originally Posted by MudColoredXJ View Post
I also had to put a helicoil in one of the holes. Quite possibly the worst experience yet with my jeep.
i loath helicoils, i feel your pain

-matt
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Unread 08-16-2008, 07:52 PM   #5
BrunoS
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160 miles later...holding up well with the repair. Have now had several near full throttle freeway onramp blasts. The motor mount repair and all new bolts on both sides have really smoothed out engine vibration and accelerations feel "tighter" with less motor wobble. Jeimminny, wish I had known about this years ago!


Should be among the top things to check on any XJ besides a worn out cooling (primary) fan clutch!!!!
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Newly Painted! Emerald Green '96 XJ 4x4 4.0 HO 5-spd
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Drilled out Stock Airbox / Gauge Cluster Upgrade
Magnaflow Muffler / High-flo Cat / MSD Coil

Last edited by BrunoS; 08-18-2008 at 03:57 PM.. Reason: newer info.
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Unread 08-16-2008, 08:11 PM   #6
91HeAp
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Quote:
Originally Posted by BrunoS View Post
100 miles later...holding up well with the repair.


Should be among the top things to check on XJ's besides the fan clutch!!!!
Newbe XJ (and Jeep) owner. check the fan clutch? thanks for the advice above will be under the ol' girl tomorrow.
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Unread 08-16-2008, 09:42 PM   #7
kadetklapp
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Yes, grade 5 hardware for teh suck.
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Unread 08-17-2008, 11:03 AM   #8
BrunoS
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Correct bolts for engine mount bolts that go into the block are Grade 5. You could use Grade 8, but good luck drilling those out if they should ever fail.
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Newly Painted! Emerald Green '96 XJ 4x4 4.0 HO 5-spd
3" Lift + 31" Tires / D35 TracLok / NP231
Drilled out Stock Airbox / Gauge Cluster Upgrade
Magnaflow Muffler / High-flo Cat / MSD Coil
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Unread 08-17-2008, 01:31 PM   #9
Saudade
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Best set of easy outs I've ever used.



The easy out itself is straight and fluted.



Each size has a matching collar that slips over it and allow the collar to slide up against the broken bolt/stud. This applies all of the torque to twist out the broken piece without snapping the easyout.



Using these, a right angle drill attachment and a centering drill, I was able to get the 2 broken bolts out of the block when my snapped off.
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Unread 08-17-2008, 01:32 PM   #10
Si1ver03Rubicon
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^ We use those exact ones in the military.
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Unread 08-17-2008, 03:46 PM   #11
JeepRide
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What is the brand name of those ez outs and where did you get them?
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Unread 09-25-2008, 08:39 PM   #12
rod_serengeti
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In 252,410 miles, X2 motor mount bolts. The first set failed in 2003 at 142,000 or so miles. This set lasted until I hit a big rut on a forest road.

Now there's grade 8 bolts in there. I have to figure these will at least out last the original engine.
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Unread 09-25-2008, 09:14 PM   #13
TwistedcaB-
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could a vibrating at low speeds ( like parking lots ) till u get on the gas a little be motor mounts bein loose?
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Unread 09-25-2008, 09:36 PM   #14
jeep_rider
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Has mileage always above the 100k mark?
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Unread 09-25-2008, 09:44 PM   #15
TwistedcaB-
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if ur talkin to me i have 180k
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1991 XJ. 8" lift, 35" BFG KM2's. the new project
1990 XJ. 6.5 lift, 33" BFG ATKO's. SOLD : (
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