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  #1  
Old April 29th, 2005, 09:34
4Squirrels 4Squirrels is offline
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Chrysler's Loving Gift to Jeep 4.0L Owners

So, back in late January, I was heading up Rampart to the shooting range when I heard a pleasant little slam, and the engine died. I got out, checked, and it turns out the passenger side engine mounts bolts that tap into the block sheared off. Kinda shitty. One of the three took a portion of block with it. My buddy and I cradled the engine using a ratcheting strap, and drove it home with no passenger motor mount.



Well, after lots of repositioning of engine bay components, we got enough room to get a left-hand drill bit and angle drill in to get the bolts out. They came out with minimal effort. I had three grade 8 laying around, so I put two on the passenger side, pulled a factory one from the drivers side and put it on the passenger side, and replaced it with a grade 8 on the drivers side. Iím wishing I had gone out and replaced them all with grade 8ís.



Sunday, coming back from Chinamanís Gulch, I noticed a new light slapping sound on acceleration. I checked it out last night to find that the factory bolt on the passenger side had sheared offÖ again. So, Iím back to where I started. Now I have to pull a bunch of BS, position stuff just right, and then drill the sheared bolt out because Chrysler did not do enough materials testing to figure out that a stronger bolt might be necessary. I have never jumped my rig, and Iím as easy on the gas as I can be for 35ís and 4.56ís. I tell you, the engineer that decided to put anything other then grade 8 in for engine mounts should be taken to the pasture and shot.



Has anyone else has similar experience? If not, do yourself a favor, and replace them before they break. Hereís what I replaced them with 3/8 x 1.28 Ė 16 with a washer for a touch of extra spacing. I will be doing the whole thing again tonight. Fun fun.
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  #2  
Old April 29th, 2005, 12:06
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explorer explorer is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

Check to see if the bolts are bottoming in the hole. Your problem is not uncommon, and bolt length was an issue. They would bottom in the hole, but just barely snug up the mount bracket to the engine block. I've replaced lots of them w/ grade 5 hardware, just shorter, and never had problems after that. When the bolt bottoms in the hole, it fatigues because the mount can move slightly back and forth weakening it.
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Old April 29th, 2005, 12:33
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ChuckD ChuckD is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

[QUOTE=4Squirrels

Chrysler did not do enough materials testing to figure out that a stronger bolt might be necessary. I have never jumped my rig, and Iím as easy on the gas as I can be for 35ís and 4.56ís. I tell you, the engineer that decided to put anything other then grade 8 in for engine mounts should be taken to the pasture and shot. [/QUOTE]


Chysler also didn't intend for you to add 35's and 4.56 gears.
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  #4  
Old April 29th, 2005, 12:35
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490Chaser 490Chaser is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

That's chrysler though... great engineering, craptastic materials
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  #5  
Old April 29th, 2005, 13:14
SteveT SteveT is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

Yeah, happened to me a little over a year ago. Turns out the highest/hardest to get to bolt was broken and never replaced, so I had been running on 2. It was broken off about 1/2" inside the block. Tried running on 2...broke again while mudding. I broke 2 EZ outs and a left hand bit trying to fix it.
Finally found a guy who could get the tip of welding rod to touch the busted bolt shaft, and build up some material, the weld a nut on, and twist it out. $105 later, 6 grade 8's, and some M.O.R.E. mounts (just 'cause I was there), and I was good to go.

Steve
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  #6  
Old April 29th, 2005, 16:38
4Squirrels 4Squirrels is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

Quote:
Originally Posted by explorer
Check to see if the bolts are bottoming in the hole. Your problem is not uncommon, and bolt length was an issue. They would bottom in the hole, but just barely snug up the mount bracket to the engine block. I've replaced lots of them w/ grade 5 hardware, just shorter, and never had problems after that. When the bolt bottoms in the hole, it fatigues because the mount can move slightly back and forth weakening it.
Almost all machined holes in blocks are overtapped in depth. However, I add two washers to ensure I was not bottoming the bolt out since I'm replacing a 1.125" long bolt with a 1.250" bolt. Good suggestion. Thank you.

Quote:
Originally Posted by ChuckD
Chysler also didn't intend for you to add 35's and 4.56 gears.
Good point. I wish they had. It'd make our lives sooo much better.
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  #7  
Old April 29th, 2005, 20:25
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

Might want to take a look at the tranny mount while you are in the process of you doing your motor mounts. The tranny mounts aren't the best in the world.
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  #8  
Old April 29th, 2005, 20:46
Whitetail Whitetail is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

Arent Grade 5's better for an application where theres constant movement on the bolt?
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  #9  
Old April 30th, 2005, 04:43
Sarge Sarge is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

Not an expert here but grade 5 bolts are better if there is shear potential and grade 8 where the force is linear with the bolt. In most cases grade 8 will do the job in motor mounts tho.

Sarge
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  #10  
Old April 30th, 2005, 06:25
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BigDawgz BigDawgz is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

I'd suggest grade 5's as well...for the simple fact that they will actually give a little bit more "stretch" than the grade 8's. In some instances this "stretch" helps in preventing bolt shear.

I also agree with what was said by Sarge. It's really just a matter of personal preference...and either grade of bolt...will DEFINITELY be better than the stock ones.

HAHA...Sarge....we have the same # of posts....on this one...lol.

Aron
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  #11  
Old April 30th, 2005, 07:30
Bender Bender is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

Grade 8 bolts are stronger than grade 5 bolts in shear and axial tension.

When the grade 5 bolt has reached its yield stress and started stretching the grade 8 will still be in its working range.
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  #12  
Old April 30th, 2005, 08:09
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rockwerks rockwerks is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

I had it happe on my 95 a few months back about 90 miles from home, was a long slow trip back to flagstaff, For everyone who has had it happen what year is your rig?

my 88, 89 's never had problem but the 95 has
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  #13  
Old April 30th, 2005, 09:54
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

I'm with Bender regarding the difference between bolt grades. The grade 8 is a higher strength steel, period. It doesn't matter if its loaded in shear or tension. Yes, the 5 will have more give, because it is softer. But it will have stretched and broken long before the 8 gives up.

Xjnation, all the Jeeps I did this repair on seemed to fall in the mid 90's years. I don't recall specifically what years. I started wrenching on Jeeps at the end of 95, and saw several early on. After about a year, didn't see many. But when they would occasionally come in w/ broken mount bolts, they were teh mid 90's vintage. Like I said, I bbelieve the problem was the bolts being too long. Either they werent tapping the holes deep enough for the existing bolt they were using, or they started using a slightly longer bolt. I guess I didn't check to see which changed. I just drilled them out and replaced them, making sure the new bolts were the correct length. I just used grade 5 bolts out of our bulk bins. Never saw one come back again after proper bolts were used.
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  #14  
Old April 30th, 2005, 11:02
4Squirrels 4Squirrels is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

Thank you explorer. I replaced the broken little guy with a grade 8. Hopefully, this will be the last, because spending a couple hours getting enough room for an angle drill is tedious.

I also talked to a friend who was his hands in one of the Jeep Speed jeeps. He says they used to do this all the time. He said the problem was not the shear, but the normal force. The unibody rails are diaphragming under load (fully flexed). The rails move, and change the distance between the mounts. This either pulls or pushes the mount into the block. His solution, which has fixed the problem entirely, was put an additional truss under the engine that connects the frame rails at the motor mounts. Hasn't broken any grade 8's since that truss. So, guess what I'm doing next week.
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  #15  
Old April 30th, 2005, 11:25
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RichP RichP is offline
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Re: Chrysler's Loving Gift to Jeep 4.0L Owners

Get a pic and specs on the truss. Does it replace the motor mounts or attach somewhere else... if done like I'm thinking in my head you could also incorporate an oil pan skid on there too...
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