986 motor mount

[flmont]

I bought the new motor mount for my 02' 986 2.7,.But I did not buy the shims,.will the upgraded factory mount require the shims,.?? pelican says yes,..

but the press in mount does not require shims so Iam told,..true or false. Thanks Frank

[obthomas]

I just changed the motor mount on my 2003 3.2 and though I do not know, I suspect it is very much like your 2002 2.7. I think what you are calling shims are the thick rubber like pads each side of the mount. I bought them not knowing what to expect and found that I wasted my money because those side pads are sort of bumpers for extreme movement of the engine. My pads were like brand new so I didn't need to replace them.

[flmont]

ahh ok..thanks how long did that job take..?? Thanks Frank

[jluetjen]

In addition to up and down vibration, the engine also has rocking forces side to side from the crown-wheel pinion which are predominantly taken up by the transmission mounts, but I could picture the front of the engine having some movement. The shims would seem to help to ensure isolation of the mount from the chassis.

I'm pretty sure that I've got a bad engine mount in my car too and I suspect that under load the engine is rocking side-to-side because I can hear a rumble when the engine is under load above 4K rpm, but only in top gear. What is different between 5th gear and the others? The total load on the engine. A sudden lift-off of the throttle at that speed will also result in more rumble as (I suspect) the engine rocks back in the other direction on overrun.

Just my $0.02 of what is happening.

[flmont]

for my issue it seems to be moving around if I get on it fairly hard there is definite movement in the engine bay and its starts to vibrate just as I hit 80 MPH and it stays until I slow down...so mount is the first thing for me to check out ! Thanks

[Brian in Tucson]

Reuse the parts from the old motor mount. It will be okay. I had a machine shop down near the University press the old one out and press the new one in. As I remember it was about $30.

[obthomas]

Originally Posted by flmont

ahh ok..thanks how long did that job take..?? Thanks Frank

Took me about 2 hours

[jluetjen]

Here's a picture of the motor mount that I took out of my car next to the new one from our host (which has a 987... part number).



1) You can see how the mount from the car is cracked almost the whole way around
2) You can also see how Porsche redesigned the insert with a different arrangement for the hub and the rubber portion.
3) When replacing the inserts, note that there is a specific alignment when putting it into the carrier. I used a couple of bolts dropped through the holes of both units to make sure that they were aligned the same way. Then I used a sharpie to mark the outside of the new insert with a mark which needs to be aligned with a corresponding mark that I placed on the carrier. If you put it in wrong, you'll have a bunch of work removing the insert and then figuring out the right way to align it without the alignment of the old insert for reference.
Actually -- looking at the picture just now I can see that there is a notch in the carrier that aligns with the closest side of insert. No need for a sharpie!
4) I was able to remove the mount and cradle fairly easily from my car without draining the coolent. It looks like the hoses underneath it are fairly new since they were still supple.
5) Removing the studs helps since it will give you an extra degree of freedom in getting out from the car. The studs have a clever design with a hex head on them. You can just use a 7 mm socket to remove any which don't come out on their own, or to reinstall them.

[jluetjen]

Just a quick "after action review...

I had the local shop that pressed in the motor mount use the same alignment as the old one (based on the bolt-holes). They were pretty busy and ultimately did it for no-charge after about a week. When I went to install the matching shims that I also got from Pelican, I discovered that they didn't align correctly on the motor mount holder.

So in the picture above -- with the old motor mount in the holder, the shims would have been installed with the long end towards the right. When I had the new motor mount installed in the holder, and went to put on the shims, they now had the long side to the left. It was the only way that they could fit on the core of the mount (but they now interfered with the small flange that you can see toward the top center of the picture)

Hmmmm...

I wasn't going to take the mount back and pester the shop that did me the favor a second time, and I wanted to get the car back on the road and out of the garage so I finished the installation for now using the hold shims, which were trimmed to fit the new mount.

Results? A definite improvement, especially at the 4000 RPM plus zone of the rev range where the car used to have a significant rumble. But -- I can still hear the rumble there, but it is about 80% subdued.

Theories?

1) At some point the mount had been replaced and installed up-side down prior to my purchase of the car.
2) Even though the arrangement of the rubber in the mount is similar in both versions, Porsche for whatever reason decided to now align the 987 mounts 180-degrees from the 986 mounts.

I suspect that the 2nd theory may be correct. I'm planning on getting a lift this winter and then I'll go back and pull the mount again and have the alignment flipped to match the new shims. I suspect that they will change the frequency of the mount in the 4000 RPM range and quiet the residual boom that still remains.

I'll post the results after I do that.

[obthomas]

This is my opinion and is based on judgement as a mechanical engineer. I could be wrong but do not think so.

Look at the rubber. When the mount is installed the rubber should be in best position to hold up the engine with the rubber in compression. If the rubber appears to be mostly in tension to hold up the engine the mount is upside down.

[jluetjen]

While I understand your logic, I'm not sure if the Porsche engineers are thinking along the same lines that you are. Courtesy of our host, here's a picture of one of the "shims" that I received.



Note that the fat side of the egg-shaped cut-out is aligned with the long side of the shim. Compare this to the picture above.

[obthomas]

I put my new mount back in comparing the rubber moldings of the old. As I said in my earliest post I ordered new shims also and ended up re-using the old ones because they were like new and the cutout of the new ones was different than original. Anyway, good luck.

[obthomas]

Another piece of logic. Lets say I was not replacing the motor mount, only the shims. The new shims would therefore be a better fit for the old mount

[obthomas]

Another thought. Somewhere in the back of my mind replacing the motor mount bushing instead of the whole motor mount came about because someone discovered that a 996 bushing would work. I don't think the busing we are all using was originally available separately from the mount bracket for the boxster.

[jluetjen]

Originally Posted by obthomas

Another piece of logic. Lets say I was not replacing the motor mount, only the shims. The new shims would therefore be a better fit for the old mount

Not really. The center core has a different shape. The early style ( part number 986...) has a roughly diamond pattern while the later style (987...) has a tear-drop shaped core.

[jluetjen]

Originally Posted by obthomas

Another piece of logic. Lets say I was not replacing the motor mount, only the shims. The new shims would therefore be a better fit for the old mount

Speaking of the shims -- note that they are actually now made of 2 materials. I have no clue which side should be out, or if it makes a difference.

[flmont]

on my old mount you could see where the shims or pads where on the sides of the mount,.2 very shinny spots,.. I will try to load a pic !

[jluetjen]

Yeah flmont, I noticed that too -- after the fact!

[DMadigan]

I see you discovered the same thing that I did on my '98. See my "rumble on hard left turn". The teardrop mount should be installed 180 degrees out from the original diamond core damper. Otherwise the support stop pads point outward from the frame mount and will not hit the flanges. Also, as you noted, the core will be supported hanging on the rubber rather than sitting in compression on the rubber.
In Pelican's DIY replacement of the mount they do not say there is a different support stop for the teardrop core damper. The parts only show the diamond shape. You have to modify the stop as I showed in my posting to fit the teardrop if you do not get the correct stop.
Though, I think if I did this again I would get a piece of Delrin and make the stops. There is nothing critical in the dimensions. They float between the engine and frame mounts.
To me they are fairly expensive for a little piece of plastic. A 6" x 6" piece of Delrin costs less than one stop plate. On another site the stop cost more than the damper!