w123 engine mount 8mm bolt height issue - PeachParts Mercedes-Benz Forum

JHZR2 · #1 02-28-2010, 07:39 PM

Height isnt the best way to explain it, but here it goes... Had to remove the 8mm bolts to do an oil cooler hose job. Got the hoses in really easy with my wife up top, far better than removing the old ones.

Putting everything back together, of course the mounts need to get reconnected via the 8mm hex bolts.

The one on the driver's side went in and is way far up in the hole when fully tight. The passenger's side one is just inside of the hole in the frame when fully tightened. Both took about the same time to ratchet, so I don't think it is an issue of one not being in all the way.

I took some pics, not sure if they are very telling...

Driver's side:

Passenger's side

From the top:

Biodiesel300TD · #2 02-28-2010, 08:16 PM

I've had this happen before on a couple of cars, and it's because the bolt is cross threaded in the mount. It's really east to get them cross threaded since the mount arm is aluminum. If you haven't really torqued it down you might be able to get the bolt in correctly. Pull the bolt out and look up into the hole and make sure the arm is sitting centered in the mount. They often don't line up very well once the bolts have been taken out and the engine jacked up. You might have to push the engine one way or another to center it then put the bolt in.

JHZR2 · #3 02-28-2010, 08:41 PM

Is there an operational way that I can tell if the bolt is cross-threaded in? I had no resistance going in, and it has threaded a LONG way up... So even if it is cross-threaded, there is a significant amount of bolt thread, threaded into the arm.

Wish I recalled how it looked before taking off the 8mm bolts. Nothing did look misaligned though, and the holes took up the threads fairly easily... if anything the hole more misaligned was on the passenger driver's side, which is the one that went further up...

Will I loose some functionality of the mount, some lack of dampening or similar if the bolt is cross-threaded?

Can one purchase a new mount arm?

Thanks!

Biodiesel300TD · #4 02-28-2010, 09:13 PM

I've had the same experience. I usually hand thread them in as much as possible to eliminate any cross threading, but thats the only conclusion that I could come up with when it happened to me. I tried many times to get it in properly but it wouldn't go. There is a possibility that one of the holes is shorter than the other, and that one bolt it shorter than the other, but I can't confirm that. You could always stack up some washers to take up the extra space, assuming the bolt is bottoming out and not holding tight against the frame.

Diesel911 · #5 02-28-2010, 09:26 PM

I did not even get mine in that far before I mess the Threads up.
What I found out is when one Bolt is in do not tighten it until both are in. It gives you a little more play to shift the Engine around until it is lined up before you install that last bolt.

I was able to get a tap and chase my threads.

I believe one of the Members simply drilled all the way through his arm and installed a long Bolt with a nut on it.

Also if you remove the Arm from the Block you should be able to install one of the Thread Restoration Inserts.

JHZR2 · #6 02-28-2010, 09:26 PM

They each go to "wrist tight" with a 3/8" ratchet. I havent looked up the spec to torque to...

Both bolts looked identical.

Could/would a collapsed mount cause the bolt to tighten up to a different point w/r/t the hole that one accesses it through? My mounts have 6 years and 10k on them. Certainly look OK but time takes its toll and it is not clear to me that they are each the same height...

JHZR2 · #7 02-28-2010, 09:29 PM

Quote:

Originally Posted by Diesel911

I did not even get mine in that far before I mess the Threads up.
What I found out is when one is in do not tighten it until both are in. It gives you a little more play to shift the Engine around until it is lined up before you install that last bolt.

I'm not 100% sure that one is cross-threaded. If it is, the cross-thread still allows the bolts to go to the point where they can be torqued to spec, FWIW.

So long as it is still going to allow full function, I may not bother worrying about it for now.

Biodiesel300TD · #8 02-28-2010, 09:40 PM

Quote:

Originally Posted by Diesel911

What I found out is when one Bolt is in do not tighten it until both are in. It gives you a little more play to shift the Engine around until it is lined up before you install that last bolt.

Thats how I do it now too. I get them all started. Once they are all started then I tighten them down.

Quote:

Originally Posted by JHZR2

Could/would a collapsed mount cause the bolt to tighten up to a different point w/r/t the hole that one accesses it through? My mounts have 6 years and 10k on them. Certainly look OK but time takes its toll and it is not clear to me that they are each the same height...

A completely torn mount might cause problems with a bolt or threads, but I wouldn't think that a collapsed mount would do anything.

JHZR2 · #9 02-28-2010, 10:01 PM

Well wouldnt the mount effect the space between the arm and the hole in the car? If the engine is sitting lower, Id imagine the top of the bolt hole would also be sitting lower, right?

Or does the engine actually rest on something else, giving the two arms the same heigt whether the mount is good or not?

Biodiesel300TD · #10 02-28-2010, 10:40 PM

Yes, a compressed mount would cause the bolt to sit lower. That would actually make sense, due to the passenger side mounts getting compressed from the rotation of the engine, and the drivers side mount gets pull on.

babyjames · #11 02-28-2010, 11:01 PM

Shot mount on the right side gets my vote. Why'd you take that bolt out, anyway?

Regardless, stick your floor jack under the pan (with a board between saddle and pan, of course) and lift the engine a little with the bolts in the arms - like you have it right now, ya' know, with the bolts in and tight. Then wiggle in there and see if the bolt head is in the more-or-less "proper" position. If so, that mount is a goner.

Jay.

charmalu · #12 03-01-2010, 06:41 AM

A couple years ago, I helped a Forum member replace the motor mounts on his CD. We got one side in, but the other side would not quite line up.

He took it for a ride down our windy, bumpy county road. when he came back and ran it up on the ramps, it was lined up. then the bolt went right in and we tightened them down.

Charlie

my83300cd · #13 03-01-2010, 09:09 AM

The first photo shows that the bolts that fasten the mount to the car frame. It looks as if one of those bolts is not tightened fully-is there something not allowing the mount to seat on the frame properly?

JHZR2 · #14 03-01-2010, 10:38 AM

Quote:

Originally Posted by my83300cd

The first photo shows that the bolts that fasten the mount to the car frame. It looks as if one of those bolts is not tightened fully-is there something not allowing the mount to seat on the frame properly?

That is a good point - took it most of the way out as I was going to remove the mount completely when doing the oil lines.

It was the driver's side - the one that goes further up... It looked that way when I did it the first time, with it loose, and even after I relifted the engine and tightened it - and dud it again, it still looked that way...

In my mind it is the passenger side one that is more of an issue - it is the one where the bolt is far further down. Maybe it is cross threaded, I don't know and can't tell. When I start using the car will I know if the 8mm isn't properly tightened? If so, how?

I took both 8mm bolts out to make it easy to lift the engine to do the oil cooler lines. I figured jacking the whole engine with one side stationary couldn't be good for anything...

JHZR2 · #15 03-06-2010, 11:14 PM

A collapsed mount it was. Getting ready to close everything up and get the car ready to drive, I took a few more hard looks at it. The side with the lower bolt was definitely sitting lower.

Called the second-closest MB dealer (closest one isnt open on Saturday), and my wife was nice enough to drive down to pick up two in-stock mounts.

Got the 6mm bolts out, pulled the mounts and this is what I found:

Note that the two on the outsides are brand new.

The collapsed one was the passenger (turbo) side.