Daniel5691

Hello !
I have a few questions about the 928 motor mounts...

In what model year were the original design OB mounts replaced by the newer design ?

Are there further design differences within these 2 types? (Are all "old" mounts and all "newer" mounts the same?)

I understand that the newer mounts are most easily installed by also using a newer design crossmember.

Are there also mounting differences for the newer and older styles on the engine block itself, or are the engine-side mounting points identical for both designs?

Thanks !

Dan

Rob Edwards

The early mounts were used 78-82, the new mounts are 83-95. There were at least 2 versions of the early mounts, in the first few hundred '78's, then the common version used until the end of '82. I'm not aware of any changes in the 83-95 mounts.

Discussion of the early 1978 mounts: https://rennlist.com/forums/928-foru...ne-mounts.html

No mounting differences on the engine block, the mounting ears on the block have the same spacing.

Here's the description of the new hydraulic mounts in the 1983 service info book.

Daniel5691

Thank you sir !

This site must consistently hold the record for how fast a random question can be addressed.

Have a great weekend !

Rob Edwards

It was either motor mount archaeology or autopsy reports. Easy choice.

Red Flash

Interesting description! Thanks Rob!!

So, does anybody know the actual way in which the mounts collapse/wear out? Does the elastic hollow member (part 1 above) just gradually deform? Knowing nothing about early cars, do the early mounts fail like the later mounts as well?

ROG100

The early mounts are solid rubber and rarely fail in a collapsed mode. They often become detached from the metal brackets the rubber is bonded to.
The later MM's are hollow and filled with water and a little antifreeze. They simply leak and collapse.
The main purpose of the MM is to isolate engine vibration from the chassis.

dr bob

Support in the newer-style mount is a combination of mechanical via the rubber section, and hydraulic via the fluid. The fluid flowing through that metering orifice slows the allowable travel. But like a spring-and-shock-absorber combo that holds the car up, the primary support is the rubber "spring". Also like that spring-and-shock-absorber, loss of dampening via fluid leaks, as Roger describes, pretty quickly trashes the rubber "spring". Age, heat, oil and other petro fluid exposure quickly take their toll on the rubber that contains the fluid. In their rather isolated locations it's hard to see actual leakage, but you can see the progressive effects of the loss of fluid as the engine slowly drops towards the crossmember. It's essential that you maintain the heat shields between the mounts and the exhaust system. In the S4+ cars, there are ducts in the undertray that direct airflow across that area to further protect the mounts from exhaust heat.

I replaced the original motor mounts with factory Porsche mounts. Originals were about half-collapsed when I did that first swap. Those replacements were replaced again as part of a WYAIT on a gearbox mount, engine cleaning and OPG project a dozen or so years later. This time, the popular Volvo mounts went in. Even with a dozen years and 35k miles on the intermediate set of the Porsche mounts, they had barely sagged. In fact they are still in good enough shape to go back into the usable-spares bin, in case that level of originality is needed some time in the future. Two years and a few thousand miles into the Volvo mounts now, there is no measurable sag from their installed height.

I have a used-once engine support available to anyone nearby that needs it. Had to buy one of my own after we moved too far from Rob's. Much better than a couple pieces of 4x4 under the MM brackets on the engine. So far the only MM/OPG "clinic" here has been on my own car. I kinda miss having a garage plus the driveway full of 928's for clinic days.