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Unread 07-17-2013, 08:13 AM   #1
Lonewolf92c
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1995 XJ Cherokee 
 
Join Date: Mar 2011
Location: Gravette, AR
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Pass. side motor mount bolts...HELP!

So the pass. side motor mount to block bolts sheared off AGAIN....just fixed it last fall.

This time have pulled both motor mount big bolts; pulled alternator and lowered motor as far as I could. Not much room, even with right angle drill attachment (from Harbor Freight so not the best).
1) Tried drilling center bolt for ez-out; got ez-out in, put pliers on it and snapped tip off in hole.
2) Tried drilling out front bolt and got hole started then snalled tip of bit off in hole.
3) Can't get good shot at rear most bolt.
4) Cordless, battery powered 19.2 drill so maybe not enough torque to drill well....suggestions.

Have tried heating 2-3 times each and also hit it with PB Blaster. Any and all help is appreciated at this point....I am out of ideas and not wanting to take it to someone...too much $$

Please and thanks in advance for any and all ideas!!

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Unread 07-17-2013, 08:58 AM   #2
CCKen
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Sorry I can't provided any good suggestions on how to get those bolts out, but I would like to know is: What bolts did you install last fall, factory bolts or hardware store bolts? Where they grade 8 bolts?
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Unread 07-17-2013, 09:09 AM   #3
Lonewolf92c
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Bolts...

@CCKEN...hardware store bolts and pretty suer i bought grade 8 bolts. However, when I replaced last time all bolts were sheared off. I was only able to get two forward most bolts out and went with it to get rolling again.

In retrospect, not having bolted down mount with all 3 may have put undue stress on the two that I did install.....

Thougths?
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Unread 07-17-2013, 06:48 PM   #4
CCKen
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You might try posting this on the NAXJA forum http://www.naxja. org/.
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Unread 07-17-2013, 07:21 PM   #5
KF4SQB
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If you have the equipment available, and if you are able to get to everything well enough, you may be able to weld a nut to the end of each bolt, and then use a wrench on the nut to back the bolt out. Just weld the inside of the nut to the end of the bolt. Chances are, if you can ever get the bolt to start turning, it will back on out fairly easily. Unless you put lock-tite on them.
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Unread 07-17-2013, 08:31 PM   #6
cruiser54
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Here's wHY the bolts break:

From Jon Kelley aka 5-90 @ www.kelleyswip.com



This is a known issue.

1) Unless you're going to get silly with the skinny pedal, 2xSAE8 screws on one side won't be a huge problem. You'd be better off with three, but if you don't get silly you'll be okeh.

2) The Brown Dog engine mounts use two or three additional holes on each side, and spread the mount/clamping force over more of the block. This is invariably a good idea, and I'll probably be doing it as I refit my 88.

3) The primary reason that the screws snap is because, sometimes, the screw holes in the block aren't drilled & tapped deeply enough. This causes the screw to bottom out in the hole, so you end up torquing against the bottom of the hole instead of stretching the screw (as you're supposed to do. Not your fault - you aren't doing anything wrong.) The screw is not stretched properly, and the head is not butted up against the bracket, so there's some room to move there. Vibration then causes wear cycles on the screw, which generally leads to rupture.

The easy/cheap fix? When you replace the screws (3/8"-16x1.25", as I recall,) put two flat washers under the head before you screw it into the hole.

The check? Take a feeler gage (.003" to .005") and try to slide it under the head of the screw. You'll be able to get under the corners (look at the hex head, and you'll see that the surfaces curve toward each other slightly) if it's a standard hex head - if it's a flanged hex head, you should not be able to get under the head anywhere. If you can slip the gage under the head, you have a problem. If you can touch the shank of the screw, you have a big problem!

In no case should you reuse the screws after you take them out - they'll be stressed under the head, and you'll have a significant reduction in strength. Replace them outright, putting washers under the head as I mentioned before. The washers will make up for the slight lack of depth in the hole (two of them will be about 0.125" or so,) and allow the screw to be preloaded properly.
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