NOS, Material failure or incompetence with motor mounts?

[Oldtimerfahrer]

I discovered a few months ago when replacing the pilot bearing that my engine was not sitting correctly in the motor mounts...The block on the driver's side was sitting high in the mount, so that the screw was barely holding it in the groove of the subframe. So, engine sitting too high, which I had observed before but had not removed the air filter can (ti) to see the mount. So, explained why the engine sat high. I did not obesrve any cracks on the carrier, looks like someone has beefed it up in the past.

So since the mount was crooked from sitting high, I decided to replace the mounts. I had two NOS mounts on the shelf for both sides, were probably 4 years old, never used. I replaced both sides and drove maybe 200 miles or so and then... I noticed that the mount of the driver's side has split (sheared) from the top about 2/3 of the way through the mount. Like the engine was rocking to the passenger side and tearing the mount. Is there any way to install this "incorrectly" if its sitting true in the mount and the limiter on the passenger side is set correctly? Gearbox mounts are good, no issue there.

I was unsure whether the problem is NOS item (dried out), material failure (bad batch) or my bad (incorrect install).

Since its winter in the far north and I am doing a heater box rebuild, I can take my time in fixing this, but any input would be appreciated.

Andrew

[tzei]

You had them 4 years or are they truly just 4 years old (stamps confirms)? Rubber ages so there is that but… bad batch?

Four years of intense welding near them not bagged?

[Mike Self]

Is your driver's side mount (the one you replaced) the OEM style round one inside a metal cup, or the rectangular replacement?  From your description it sounds like the latter...

 

And...is the passenger side mounting bracket the early style--a single piece of metal bent to hold the rubber mount, or the later style that's welded up from several pieces.  If the former, they will eventually stress crack and allow the motor to sag to the passenger side, thus putting extra stress on the driver's side rubber mount.  

 

mike

[Oldtimerfahrer]

On 10/15/2023 at 11:51 PM, Mike Self said:

Is your driver's side mount (the one you replaced) the OEM style round one inside a metal cup, or the rectangular replacement?  From your description it sounds like the latter...

 

And...is the passenger side mounting bracket the early style--a single piece of metal bent to hold the rubber mount, or the later style that's welded up from several pieces.  If the former, they will eventually stress crack and allow the motor to sag to the passenger side, thus putting extra stress on the driver's side rubber mount.  

 

mike

I have the round style on the drivers' side, but I can see between the cap and the mount that the mount is parting. I don't remember what the plate/bracket looks like on the passenger side, but I will check it for cracks as I will probably replace both mounts again...It would be easier to do without the skid plate under the engine, but its so hard to get it and the bumper mounts back in the frame rails in the right position.

Thanks!

Andrew

[Oldtimerfahrer]

W&N don't seem to have the round mount any more. The funky square one with a movement limiter is available. I assume they are directly interchangeable, but are there any detractors for this newer design?

Andrew

[Mark92131]

19 hours ago, Oldtimerfahrer said:

but are there any detractors for this newer design?

 

I had my motor and trans assembled in the subframe for installation from the bottom.  With the square new design, the motor and trans had significant lateral movement in the subframe that would distort the motor mount.  This lateral movement may be by design?  I switched back to the round one with the metal cup and the lateral movement was abated.  We'll see how long the round one lasts.

 

Mark92131

[NickVyse]

On 10/17/2023 at 11:15 PM, Oldtimerfahrer said:

W&N don't seem to have the round mount any more. The funky square one with a movement limiter is available. I assume they are directly interchangeable, but are there any detractors for this newer design?

Andrew

 

[Oldtimerfahrer]

The picture in the w&n website of the last mount is not confidence inspiring. It looks wider here. Looks like it would limit rocking, but not fore and aft motion.

A.

[TobyB]

The motor mounts are not limited longitundinally- 

and only the rectangular one is limited for engine rotation.

There is a separate bumper for fore- aft, and it's pretty flimsy.

 

NOS means a part made when the car was made, not an aftermarket*

part from a few years ago.

 

The round mount is completely unlimited- without the sleeve, it allows a LOT

of motor movement, and with the sleeve, it shears off at the unsleeved side.

 

Some distortion of the mount's not unusual- especially if you're not replacing the lower

mount as well.  BMW made a little buzzbox in the 2002 when the M10 went in, and the

floppy mounts were an attempt to mitigate that.  

 

t

*BMW has not made the BMW- baggied parts for quite a while now.

For example, FEBI has 2 moulds for the rockers- one has a BMW roundel,

one does not, but the rockers that come out of the moulds are identical otherwise.

BMW have a few sources we don't have access to, but it's not unusual

to discover that those sources are making pure crap.

Edited October 20, 2023 by TobyB

[Oldtimerfahrer]

Ok, my stock was "semi-old OEM" stock. I had the metal cup and will probably then search for a direct replacement, hopefully newer stock from oem supplier.

A.

[Son of Marty]

When you replace the mount leave it loose and loosen up the right side mount from both the engine side and frame side and the tranny mount and give the engine a good shake trying to get the engine to sit where it want's and the d/s mount to sit farther down.