WARNING: All 4.0 owners check your motor mount/block Bolts!!!! - Page 6 - JeepForum.com
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Unread 05-05-2009, 07:58 PM   #76
escapeartist
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Another method for drilling out broken bolts, go to a tool supply house and buy a left hand drill. Sometimes when you start drilling with one of these they catch and back the broken stud out or as the bolt warms up they come out. If it doesn't work you are no worse off and have a hole drilled the right size. The drills are usually about 10 bucks each and a higher quality cobalt HSS tool steel than the average black drills.

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Unread 05-06-2009, 09:47 PM   #77
94HOCHEROKEE
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I heard a really good idea of taking a welding rod and welding it to the bolt, then after letting it cool down twist the bolt out. I heard it from my boss at Wally world TLE express after it happend to his cherokee. I guess his insurance adjuster meantioned how to get out, said it works 90% of the time. Thanx for the lines......
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Unread 05-06-2009, 11:46 PM   #78
5-90
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A relatively common problem.

It's caused by the screws bottoming out in the holes. You're not establishing a tensile preload under the head when you torque screws that are bottomed out, you're establishing a compressive preload at the very end.

Problem is, a compressive preload in this application is totally useless.

The fix? Simplicity itself. Find out if/which screw(s) is/are bottomed out with a thin feeler gage (even .001" is too much, so use the thinnest gage you have.) If the gage slips in under the head, remove the screw and add a washer or two. Reinstall the screw and retorque.

Typically, the screw fails (due to a lack of preload and repeated shear stresses,) the head breaks off, and you're stuck with a broken screw shank. Then you have to drill and remove it - no fun.

Even with the full-length "Bombproof" engine mounts, check under the screw heads before you pronounce the job "done." Same thing - if you find any heads with room under them, install a flat washer and retorque. Easy.

If you see space under the head with your naked eyes, install two flat washers just to be safe.
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Unread 05-15-2009, 09:29 PM   #79
portcityXJ
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just ordered brown dog mounts (no brackets, just mount) with poly bushings. i had enough space to fit my entire finger in the mount above the bolt where the bushing is worn/missing.
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Do they come in any other varieties besides crap?
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Unread 09-02-2010, 08:01 PM   #80
jeepsterguy
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Quote:
Originally Posted by brand0nlp View Post
i let my motor down just undid the motor mount, used a block of wood and a jack under the oil pan and carefully dropped it oto the steering arms. but kept the jack just snug underneath it so it wouldnt put to much weight on the steering components.
I realize that the thread is old but this just happened to my '96. Did you have to use a 90* drill?
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Unread 09-02-2010, 10:21 PM   #81
brand0nlp
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no, actually when the bolts break its usually cause there already loose, i took a flat screw driver and a hammer and made indent in the bolt then i used the screw driver to take it out if the screw driver and hammer doesnt work use a thin cut off wheel, and make a slot for the screw driver. it shouldnt be that hard to take out the bolts.
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Unread 09-03-2010, 07:20 PM   #82
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Old thread, I posted it. Very important to check. As for getting bolts out, whatever works. My single new bolt and motor mount plate to block weld has still held under full dd hammering . Two bolts were impossible to remove with 4 mechanics and a full shop.....
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Unread 09-03-2010, 07:51 PM   #83
FairlanePhil
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Quote:
Originally Posted by portcityXJ View Post
just ordered brown dog mounts (no brackets, just mount) with poly bushings. i had enough space to fit my entire finger in the mount above the bolt where the bushing is worn/missing.

Vendor link please!
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Unread 09-04-2010, 12:09 PM   #84
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Quote:
Originally Posted by BrunoS View Post
Two bolts were impossible to remove with 4 mechanics and a full shop.....

I soaked them for a couple of days in Kroil, came out easily.
There is no reason that I can see for the bolts not to come out easily, the hardness of grade 8 assures a clean break and the tolerance in these bolts is sloppy. The only way I can see it happen is if the guy drills in to the threads. I used a pilot hole just to make sure I was straight and not hitting any threads. At that point I tried a small easy out and they came right off.
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Unread 03-03-2011, 03:44 PM   #85
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This issue just happened to my brother, I think i'll be changing my hardware to grade 8
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Unread 03-03-2011, 04:05 PM   #86
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Quote:
Originally Posted by gretsch921 View Post
This issue just happened to my brother, I think i'll be changing my hardware to grade 8
The original are grade 8 and they don't do very well.
I bought some socket bolts that are supposed to be better than grade 8 and will install them first chance I get.
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Unread 03-03-2011, 04:30 PM   #87
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Quote:
Originally Posted by jeepsterguy View Post
The original are grade 8 and they don't do very well.
I bought some socket bolts that are supposed to be better than grade 8 and will install them first chance I get.
I believe the originals are grade 5
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Unread 03-03-2011, 04:41 PM   #88
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Quote:
Originally Posted by limited View Post
To the guys wondering about how to replace the bolts without an engine hoist; Take a jack and center it under the oil pan and use it to take the weight off the mounts. Be sure to use a piece of wood in between the jack and pan.
how strong is the oil pan? Is it okay to support it with the jack while replacing the mounts? I've never experienced this problem but would like to know for future reference. Does this problem occur more frequently in certain years?
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Unread 03-03-2011, 04:57 PM   #89
ZexGX
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Does anybody know the length and thread pitch of the bolts to replace? Thinking of replacing these with some high quality hardware before something bad happens.

Quote:
Originally Posted by jeepkid03 View Post
how strong is the oil pan? Is it okay to support it with the jack while replacing the mounts? I've never experienced this problem but would like to know for future reference. Does this problem occur more frequently in certain years?
Exactly what I was wondering!
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Unread 03-04-2011, 06:45 PM   #90
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originals are grade 5.

Get new bolts, they're standard thread, nothing fancy, ensure new bolts are SHORTER than the factory bolts.

The factory bolts are about 1/16" too long and the bolt head does not clamp the motor mount against the block. This is what shears the bolt.

I'm at 180K DD miles, and repair is still holding.
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