Wrench (1k)  Motor Mounts and Testing
  
Torque Axis Mount

 

 
The torque axis mount is located on the top of the motor, between the cam cover and coolant overflow tank.  This mount wears out the quickest, and it is common to go through several of them during the life of the car.  If you feel vibration in the passenger compartment, or hear more engine noise than you used to, this mount is the first one you should check.
  
  
When this mount fails, the rubber either cracks or separates from the steel.  I've gone through a handful of these mounts, and here are a few photos of mine that have gone bad.
  

Crack on underside
(most common)
  
Crack on side
  


Crack on side.
  
  
The torque axis mount came in several different designs over the years, which were used during three time periods.
  

 
Design A came on S-Series cars from 1992 through 1996.  It was the stiffer of the torque axis mount designs, and resulted in the cars often being mentioned in reviews as having more vibration and engine noise than other cars in its class.  This likely prompted design B below.
  

 
Design B came on S-Series cars from 1997 through 2000.  They were a bit softer and had more compliance than Design A mounts to address the vibration/noise issue.  But the longevity was significantly shorter than the Design A above.
  
  
Design C was on S-Series cars from 2001 through 2002.  Since the design B mounts wore out very quickly, the factory went back to older, and slightly stiffer mounts.  While I call them design C here (to denote a different time period), they appear to be identical to the Design A mounts shown above.

Here are a few comparison photos:
  
When switching between design A/C and B, the factory parts manual recommends replacing the studs as well.  This is most likely due to the thickness difference of the aluminum part which can be seen in the photo above right.

SDA offers a polyeurethane insert which can be installed in a design B mount that firms it up.  Pictures of the SDA mount can be seen below.

  
  
  
  
 Important Note: A Saturn race team did some experimentation with significantly stiffer-than-stock torque axis motor mounts and ended up breaking the top of the aluminum timing cover where the mount's studs screw into it.  Apparently, some compliance/flex is necessary to absorb harmful vibration/harmonics and/or drivetrain shock that does occur.  This information was passed along by reputable source, so I do trust its accuracy.
  

 
The photo of the damaged timing cover shown here was provided by Kallisti Motorsports (thanks!).  This damage was due to a significant shock to the drivetrain which couldn't be absorbed by the compliance provided by the torque axis mount.
  
  

Measuring Actual Compliance

At the time of this writing, I have a turbo system that's under construction on my '92 SC.  The turbo is mounted high on the front of the motor, and the compressor housing will come within an inch of the bottom of the hood.  I'll need a mount setup that allows the engine to move the least amount possible.  Luckily, vibration and harshness aren't a concern since this is a track-only car.

The only way to know I'm choosing the best torque axis mount for the job is to measure the actual compliance & deflection, and the amount that the motor is able to move using each type of mount available.  The idea of how to do this came to me as I had just opened a box of popsicles.  It may be a crude solution, but it gets the job done.  A couple of popsicle sticks, some masking tape, a few zip ties, and duct tape is all it will take.  Having said that, it's obvious that I'm not an engineer so please keep that in mind.
  


Before "drive"
  

  
The basic premise is to attach a set of popsicle sticks to non-moveable reference points, which in this case, were the sides of the mount where it attached to the body of the car.  A second set of sticks was attached to those with tape, and positioned so that they touched the side of the mount attached to the motor but were allowed to move laterally.
  


After "drive"
  

  
Since the side of the mount that the sticks now touched would move with the motor, the motion of the motor side of the mount would push the sticks.  After taking a drive, the sticks would be resting in a position indicating the maximum amount that the motor had moved on its mount in each direction.
  
  
The test "drive" consisted of mostly normal driving, with a quick burnout in first gear, and one attempted in reverse.  I installed 4 mount configurations, reset the sticks each time, went on my drive, and then measured how far the sticks had moved for that mount.
  

Observations & Results

The mount configurations that I tested, and the results that I observed are as follows:
  
Mount & condition Forward
movement		 Rearward
movement		 Notes
Design A/C, virtually new condition  4 mm  9 mm  
Design A/C, well-worn with crack on underside  7 mm  11 mm Expected more of a difference compared to non-cracked version
Design B, virtually new condition  9 mm  12 mm Motor sure looks like it moved a lot when blipping manually under the hood in neutral.
Design B, virtually new condition, with SDA insert in place  8 mm  9 mm Added some noise and vibration (should be expected), see observations below.
  
A few observations and some notes:
  • The torque axis mounts were tested on my 94 SC2 daily driver.  SPS dogbone mounts were on the car at the time.
  • SDA's mount insert was easiest to install with a mallet after disassembling the 2 metal sections of the mount, lubing everything with silicone grease, and then pounding the crap out of the insert to get it in place.  The tolerances are very tight.  The SDA insert is a well-molded piece.
  • SDA's mount introduced a lot of vibration into the passenger compartment at idle, and also seemed to deepen what the exhaust tone sounded like.  Even though the sound of the exhaust was louder, it didn't sound bad.  There were some rattles from the plastic trim panels though.  At RPMs that were above idle, any added noise/vibration was no longer there or no longer noticeable.  The average Saturn owner would probably consider this added noise/harshness unacceptable and annoying, but the average Saturn owner would probably not be installing this insert anyway.  This noise/vibration should not be a surprise, and should be expected from a part upgrade like this.  Performance-oriented owners will just have to give it a try, weigh the benefits they see against the drawbacks, and make their own decision.
  • The design A/C mount with a crack appeared to still resist motion better than a design B mount with the SDA insert in place.  This seemed odd to me, but that's what the numbers/measurements showed.
  • I've seen an indication on the TurboSaturns.net forums that the SDA insert can be used with a cracked, torn, and less-than-perfect condition mount.
      

Conclusions

You can see the numbers above that come from actual measurements, and you can draw your own conclusions based on that objective information.  But for me and the reason I did these measurements - it looks like I'll be using either a design B mount with the SDA insert (since I already bought the insert), or stick with the good old design A/C.  If you're looking to firm things up and you have a design B mount, your best bet would probably be to pick up an SDA insert as it would cost significantly less than buying a design A mount new from your Saturn dealer.

I have tried to perform these measurements and write this article in the most accurate, unbiased, and objective manner possible.  If you find any inaccuracies in this article, have helpful information that could be added, or have observed behavior that contradicts what I have measured, please be sure to drop me an e-mail.

 

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