broken 4,0 engine mount

[joe_peters]

It just happened to my '96. Passenger side.
I plan to use grade 8 till I get OEM replacements.
I guess I'm going to have to buy a 90 degree attachment for my drill.

Get yourself a set of left-hand drill bits. Often times when you use them the broken piece of the bolt will back itself out. Easy-outs are aren't--break one off and you will have to GRIND it out.

Before you cinch things down with new bolts--make sure that the bolts aren't bottoming out in the holes. If they do, the engine mount bracket will slip up and down and take out the new bolts in a short time.

And I would use grade 5 in this application.

 

[xjman96]

I don't get it. The grade 8 bolts have higher both tensile and shear strength.
I wonder if I can go to a bolt place and get even stronger than 8.

 

[joe_peters]

Here you go: http://www.unbrako.com/

They are proud of their products.

 

[Mesh]

This thread is 5 years old. If you're breaking grade 8 bolts you have some other problem you need to fix.

 

[mfascuba]

I don't get it. The grade 8 bolts have higher both tensile and shear strength.
I wonder if I can go to a bolt place and get even stronger than 8.

Like Joe Peters said, if they bottom out in the block the bracket won't be tight against the block. The loose bracket will impact the bolt each time the engine jars, the static force won't break them but the dynamic (shock load) force will. A temporary fix is to stack some washers under the head of the bolt so you can tighten the whole mess up - that should get you home so you can either cut down the bolts you have or buy the right ones. Be careful about going to stainless - corrosion resistance is not necessarily stronger. I've seen some crappy stainless hardware, I'd put my money on the grd 8 hardware properly selected and installed.

Mark

 

[xjman96]

Close to 200K miles, first time they broke.
No OEM bolts available, special order. As soon as I drill them out, I need to get it together till I can get the OEM. I was thinking of getting 1 1/2" long 3/8"x16 grade 8 and cut them to 1.125" before I install them.
I drove it home, didn't know what was wrong.

 

[xjman96]

I looked at an old parts catalog I have and then called the dealer. His part number is different, it might mean a part change. Hopefully the new OEM parts fixed the problem?

 

[WrenchMonkey]

http://www.naxja.org/forum/showthread.php?t=970843

Gets good at post 13.

FWIW, I'm sure the bolts break because they factory motor mounts are schidt. The bushings wear out and let the engine jump around.

That delivers some ridiculous shock-loads to those poor little bolts.

Robert

 

[old_man]

From what I have seen, the problem is that the threaded boss on the engine is not quite deep enough and the bolt threads in and stalls just short of applying good pressure to the mount. The mount moves and leads to it breaking. I noticed this when building a motor on a stand. I simply ground the bolts a few thousandths shorter.

 

[xjman96]

From what I have seen, the problem is that the threaded boss on the engine is not quite deep enough and the bolt threads in and stalls just short of applying good pressure to the mount. The mount moves and leads to it breaking. I noticed this when building a motor on a stand. I simply ground the bolts a few thousandths shorter.

In my search I ran in to this information, which I believe is the most likely case and also that the bolts are too short.
The parts catalog calls for 3/8x16 1.125" long. I found one of the broken bolts, it is a grade 8. I bought three bolts 1" long and three 1.5" long. When i remove the bolts I'll measure the hole and use either the 1" or cut the 1.5" to the proper length.

 

[solomon7]

I had the same thing on my 96. All 3 snapped, 1 has an easy out stuck in it and it's 1'4 inch recessed. I only had 2 bolts that would work. I saw the Brown Dog mount brackets and the MOREs and they were sweet.
I was going to go with Brown Dog brackets. . They tie in in 4 places and since 1 was gone I was still sitting on 3 bolts with a worse leverage die to their angle. You can see the in my thread.
Linky to thread http://www.naxja.org/forum/showthread.php?t=1007006

The upper hole is the one I couldn't use. see the stretched triangl the other 3 would make? I couldn't trust it in the end.

I ended up finding these from Barnett Prerformance.
http://tandjperformance.com/store/index.php?main_page=product_info&cPath=1&products_id=941
Bad ass! 7 POINTS of attachment! Screw that lost hole. The other side bracket is pretty much the same, 7 points instead of 3 so ya can't lose. Gotta loosen the Alt to attach the 2 forward ones and everything fits perfectly.
.

 

[RCP Phx]

They also make mounts(block side) that allow more mointing points(bolts) for a stronger system.

 

[xjman96]

I had the same thing on my 96. All 3 snapped, 1 has an easy out stuck in it and it's 1'4 inch recessed. I only had 2 bolts that would work. I saw the Brown Dog mount brackets and the MOREs and they were sweet.
I was going to go with Brown Dog brackets. . They tie in in 4 places and since 1 was gone I was still sitting on 3 bolts with a worse leverage die to their angle. You can see the in my thread.
Linky to thread http://www.naxja.org/forum/showthread.php?t=1007006

The upper hole is the one I couldn't use. see the stretched triangl the other 3 would make? I couldn't trust it in the end.

I ended up finding these from Barnett Prerformance.
http://tandjperformance.com/store/index.php?main_page=product_info&cPath=1&products_id=941
Bad ass! 7 POINTS of attachment! Screw that lost hole. The other side bracket is pretty much the same, 7 points instead of 3 so ya can't lose. Gotta loosen the Alt to attach the 2 forward ones and everything fits perfectly.
.

Looks like you had lotsa fun.
Tomorrow I will drill and easy out mine. The plan is to use a #3 easy out in case it is loose, if it wont do it Ill go for a #4. I have a carbide drill and carbide rotary files that can eat through the easy out which is hardened steel, softer than carbide, in case I break the extractor.
I have been soaking the holes in kroil since yesterday.

 

[old_man]

ATF mixed with acetone works the best.

 

[xjman96]

ATF mixed with acetone works the best.

I am out of acetone right now, I'll keep it in mind. What ratio?

 

[Shorty]

50/50 did wonders when I used it-- I don't know if it's the best mix, but I'll stick with it.

 

[NorCalChris]

happened to me about our months ago. i bought new grade 8 bolts for 5 bucks at napa. havent had an issue with them since.

 

[xjman96]

Looks like you had lotsa fun.
Tomorrow I will drill and easy out mine. The plan is to use a #3 easy out in case it is loose, if it wont do it Ill go for a #4. I have a carbide drill and carbide rotary files that can eat through the easy out which is hardened steel, softer than carbide, in case I break the extractor.
I have been soaking the holes in kroil since yesterday.

Done. I drilled a #40 pilot hole to make sure I'm centered and then I thought what the heck I'll try a small easy out just to see if it is loose. Came right out.
All this soaking with Kroil paid off. Grade 8 is not that hard to drill but I think it is best to start small.
A lot of people think that the problem happens because the bolts bottom down. Not in my case, in fact the replacement bolts were cut just a few thousands longer than the original, there was plenty of room in the holes.
I think they loosen up and eventually shear.
Thanks everybody for the information you provided.

 

[GrimmJeeper]

I am out of acetone right now, I'll keep it in mind. What ratio?

I've used brake cleaner with good results too, any strong solvent mixed 50/50 or so with oil makes a great penetrating lube.

 

[xjman96]

I've used brake cleaner with good results too, any strong solvent mixed 50/50 or so with oil makes a great penetrating lube.

I have been using Kroil lately and so far it seems to get right in there.
A short while ago I did the rear socks, I soaked the top bolts overnight, the next morning they came right off and looked like the kroil reached them.
I think I'll stick with it.