After reading up on the motor mount/engine block bolts I decided to

check them. I did not put a socket on them and try to turn them, I just

grabbed them with my fingers and a rag to see if they were there or

loose. They

are there but one of them, on the passenger side does not have a

hex head it is a torx. Is that normal?


Thanks.

 

Welcome to CF. Someone must have replaced that one bolt. Put a wrench on the bolts and make sure they're tight. Good luck.

 

the joys of a pre enjoyed jeep

mine has so many mismatched bolts i just haul the whole tool set out now :|

 

Thanks I will gently make sure they are tight.

And yea, The previous owner put in a radiator but I think its the wrong one, a massive trans cooler line leak at one of the quick disconnects, a rebuilt transmission but the not so competent trans shop did not fix the smashed cooler line and they reused the old mount that was trashed and falling apart...

 

I look at these situations as opportunities to upgrade. As in, "Aw, my motor mount has a mismatched bolt. I better just replace the whole thing with Brown Dog mounts and brackets."

 

Why gently? Put full torque to them, they need to be tight.

 

I almost ordered the brown dog mounts but I need to get this running asap, I just replaced the drivers side damper.
It seems that the passenger side was already replaced.

I want to crank them gently so I dont break one off.

 

If the bolts are all rusty spray them with PB Blaster for several days before working on them and see if that helps, might save on a few broken bolts.

The Brown Dog mounts are HD but they take much longer to install also and being solid you will feel the engine vibration's a lot more also over the rubber.

 

6 months ago I had a catastrophic failure of these bolts securing the motor mount bracket to the engine block. There are three on each side. On the failed side, one had long ago lost its head. Two remaining ones failed and the engine fell down to the right. Only thing that kept the matter from getting worse was the alternator came to rest on the long bolt stub securing the recovery hook bracket to the chassis rail.

Before failure, these are easy to replace. Since your vehicle is of unknown history unless you bought it new, I would suggest replacing the bolts TODAY with grade 8 bolts. (a 5$ investment and 30 minutes of time). Once they break they are a total PITA to get out.

And just testing tightness of what you have may mean nothing. Putting a wrench on them and snugging them up is not a good solution. These things fail from fatigue and other technical issues. If 20 years of fatigue has worked them over, tight today could mean snapped tomorrow.

Check this forum. There are total horror stories of what happens when your engine falls down.

 

Yea, I was also thinking of replacing them.

Is there any problem with taking them out one by one and replacing them?

I did several searches and could not find the correct bolt size and thread

pitch. Anyone have any idea what size they are?

Even though they look really cheap I think I will stick with the stock mounts.

Thanks

 

Nicksan-

I used standard mounts. No problem. Real happy with them and not a lot of expense.

Yes, you can remove the bracket bolts and replace them one at a time. They are SAE 3/8" course thread. About 3/4" length. Pull out a center one and to go the hardware store to size up a replacement. Use grade 8. Get some washers too. Install with some loctite.

Motor mount bolts are Metric (as is the whole chassis). Engine bolts on the 4.0L are SAE. The bracket is in between the chassis and engine, but uses SAE. I found this out the hard way. (The 2.8 chevy v6 in 84-89 XJ's was all metric).

Be sure the bolts tighten against the bracket. Use washers in make sure they don't bottom out in the holes. Some engines had shallow holes. The bolts bottomed out when torqued to spec, but never clamped the load (bracket). This allowed a micro movement of shear load which eventually fatigues the bolts until failure.

That is why doing the job now is so important. Everything is easy to reach.

Let us know how it goes.

 

Ever read this?

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.

 

Yea, I have but thanks for posting it.

I just checked them and they are all tight, even the torx one. I did not try the feeler gauge thing and I did not try to remove any as it was getting late and I dont want to open a can of worms yet
I have a few other things with the car I need to sort out first.

Thanks.

 

It wasn't all years either ya know.

What's yours?

 

1995 inline 6, 4.0 HO

Dang left out specs again....