Sab

I just had new motor mounts installed.
I decided to buy the solid rubber mounts.
They seemed to fit OK, and seemed fine just after installing them. But now I have a really nasty grinding vibration at certain RPM ranges.
The vibration is from the motor and goes away at full throttle, but gets really strong when letting off the gas and is pretty nasty at cruising.
Almost as if a bolt touches somewhere.
Any Ideas as to what may be amiss?

jeff spahn

You just may have a bolt barely touching if the motor mount bolts weren't cut short enough.

Bertrand Daoust

Touching... The steering rack tubing.
Here is another thread on a quite similar problem (yesterday):
https://rennlist.com/forums/928-foru...er-mm-job.html

Good luck.

Ducman82

heat shields?

Don Carter

Sounds like a different noise than mine, maybe something transferring engine vibration directly to some nearby metal.

SeanR

I'm curious to know what these noises are also, I've yet to encounter it but if there is something that needs to be paid attention to, I'd love to know it.

Mrmerlin

most of the noises will be either from the lower studs of the new motor mounts contacting the steering rack or the limit hooks rubbing on the cross member, also as previously mentioned check the heat shields near the exhaust manifolds.
Hopefully the MMs were installed with the 2 extra fender washers to add about 3mm thickness per side this should return the engine height to the factory spec, .
The lower studs should be trimmed so that no more than 3 threads protrude from the securing nut after its installed

Mrmerlin

Also another thing to inspect is the central heat shield since the motor has been raised there is a possibility that the cats might rub on the center heat shield.
Also inspect the V belts for the correct size sometimes if the wrong belts are used then the adjustments will pun the pulleys out too far and they may rub on the chassis or surrounding hoses

Don Carter

I'm about to go out and wrap my passenger MM hook with a shredded tennis ball, wired in place. I figure the tennis ball material is tough enough to last for a while and if the noise goes away at least I know where the problem is. If it doesn't I'll wrap the other side.

Don Carter

Success, the noise is almost completely gone, so I know it was caused by the hooks as MrMerlin suggested. I'll post details on the thread about my issue.

Sab

thanks for all the suggestions. I will get the car on the lift these days and post findings once I have them.
cheers,

Sab

The motor sits too low and touches the cross member.
It seems as if the new mounts collapse quite a bit with the motor on it.
I did not install the two washers that shipped with the mounts.
Will the two washers raise the motor sufficiently to make this work?

I am a bit worried, as I do not look forward to re-do a few more times. I have to tear it apart anyway, since one of the initial mounts was faulty and came apart.
thanks

Hilton

You fitted solid rubber mounts - they shouldn't collapse at all.

I don't mean to be an ***, but did you order the correct mounts? The early cars had solid rubber mounts from factory, but they won't fit the cars from about 84 onwards, and vice versa.

Even without washers on my S4, the sump is well clear of the cross member.

ROG100

Sab,
I assume you fitted the MM's to the 91 car?
We cut the lower stud before shipping.
I never use the spacer washers on installations that I have done myself with no issues.
Others do use them so either way works.

The rubber mounts will compress a little because of the weight of the engine.

jeff spahn

I didn't use the washers and got the mounts from Roger. They work great. They did compress a little but not enough that I fret about it.