jeepsoldier

So I have a 97xj sport 4.0 and when I hit a jersey pothole the other day I immediately got a horrible vibration. Soon as I could I stopped and looked. Only to find my motor mount was no longer holding my motor.. upon further investigation found out I was lucky that only the bolts broke. Got some new ones. My question is: with only joe shmoe tools, without removing the engine, is there a way to get clearance to drill out the bolts left in the block? Passenger side mount by the way

cruiser54

Read this and understand WHY they broke also.

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.

jeepsoldier

Thanks for the message on how the bolts break and why not to reuse them...but I was asking if there's a way I can get to them and drill them out without removing the other mount and lifting the engine

mrkauffman

you can drill out the bottom hole by dropping the motor with a jack after removing the motor mount thats not connected. i just did this. the other two holes seem like theyd need the engine dropped more cause the frame rails are in the way.

jeepsoldier

Yea, I have my bottle jack with a piece of wood between it n the oil pan. Lifted and lowered and looks like I can reach the bottom two bolts. I have an extractor. I'm still unsure about the top bolt tho

xj_maniac_newb

That is incredibly unsafe, please at least borrow some jack stands from someone.

Coach

I'm just curious, where would you put them?

xj_maniac_newb

On the bottom of the oil pan. Same damn place you're jacking.

jeepsoldier

The only jackstands I have are currently holding a Yota up so I can do a fuel tank swap. The jeep is my dd so its a necessity

Jrock(fos)

The bottle jack is dangerous business buddy. Especially when your going to be underneath and engine and releasing the mount so it's free. Go to autozone or oreillys they will let you borrow them for free. Get a floor jack from someone if you can.

jeepsoldier

Ok, I understand that but I grew up wit old heads who always made due wit what they had. My engine is already safely supported by my jack n the mount already removed. Did all this before posting this.all I need is advice on how is the best way to drill out the holes

MtnHermit

I have the same XJ as the OP. Didn't know about the MM known problem.

When it warms this spring I'll try your feeler gauge test.

Thanks for the post.

Jrock(fos)

Right angle drill maybe

Gentry

Ya so the motor doesn't drop on your head if the jack gives out. but when you drill them out use a left handed drill bit with the drill in reverse, 9 times out of 10 it will heat the bolt up and eventually grab, unscrewing the bolt out. And if it doesn't you still have the hole you need to use the "easy out" or "extractor." Makes it faster

jebmccall

if you have to use extractors, dont use cheap ones as they are more likely to snap off and good luck drilling a broken extractor....