I've filled my rear motor mount!

Richard_rsp · Sep 25, 2011

Ok, for those of you that haven't followed my thread in the Autocross section, I have decided to fill my stock motor mount with urethane. The benefit to this will hopefully be less sloppy shifts and reduced engine movement. I have the AWR mount, but decided to go a different route.

The AWR motor mount compared to stock

After some minor research, I ran across several DIY from people who had filled the gapped areas in their motor mounts. I decided to follow the advice of one of these DIYers and try it on our rear mount: (only thing different is that I used 60A urethane because my car is daily driven, and degreaser instead of MEK to clean the rubber mount. )

60A is right in the middle... not too hard but (hopefully) not too soft. I figure with 1.5L of fury, there is not much torque against it and 60A would be plenty.

This is what i used, 60A Durometer liquid urethane. (McMaster Carr Part no. 8644K24)

Look at all that space to be filled!

Hmm flashing that needs to be trimmed....

I taped off one side using duct tape per the instructions. I did not get a picture of this for some reason.. :shrug:

Leveling. Getting ready to pour it in...

Poured. The stuff is like syrup. Due to the chemical reaction, the liquid is warm... weird.

After a few hours:
Pretty side

Not so pretty side

The duct tape was a little difficult to remove without tearing the urethane. I don't know if it would be better to leave it on longer (so the urethane would be harder), or to have removed it sooner.

It takes a full 2 days to harden to 90% and won't be hardened fully for 7 days. I will likely install after 2 days and get an idea on the amount of NVH that occurs.

So far, easy, easy, easy...

I will continue to update once I can get it installed....

drop360 · Sep 26, 2011

First, I think this is awesome. I'm all for PWMTOS (people who make their own stuff). But I do have a couple questions.

What is your expectation for longevity? It seems if you make one part stiffer, then the forces will be moved to another part of the mount and could over stress it. I'm thinking the thinner area with the big hole in it might break. Secondly, is this kind of modification going against the spirit of the rule for ST class? I know you posted the rule and it only mentioned extra metal, but I'm curious what is implied by that. Maybe a higher durometer mount is typical. I can see how it might be.

Anyway, good stuff! I'm looking forward to hearing how it goes, in the short term as well as long term.

Richard_rsp · Sep 26, 2011

Thanks!

As for your questions:
Longevity, I am not 100% sure. This is my first time doing this and we will have to see how this mount holds up. I havent heard of anyone else with a 2 trying this yet, but there have been excellent results in other vehicles (I've read of civics with 60k miles on urethane filled mounts). I do know that the mount is only $48 to replace and the urethane is $33, so if it holds up for 30k, I will be happy...

As for vibration, I would imagine what damages these types of mounts is the constant large movement back and forth as the engine moves. Engine mounts are normally designed to reduce vibration into the cabin of the car. This mount actually will limit this movement (and in turn will likely increase vibration in the cabin). I was originally concerned about the strength of the middle section (with the hole) and almost filled it too, but after looking at it more in depth, it is STRONG, much stronger than it looks. It's rubber with metal surrounding it. Given that our cars are lightweight with relatively low power, I'm not that concerned about it breaking. Unfortunately I still believe this is uncharted territory.

I don't believe this mount is against ST spirit. ST is for 'street touring' and is designed for mild bolt on upgrades such as intakes, exhausts, ecu reflashes, and lightweight pullies. The rules read:

J. Engine mounts may be replaced, but must attach in the factory location(s) without additional modiﬁcation or changes. Engine position may not be changed. The volume of metal in a replacement
mount may not be increased relative to the volume of metal found in a stock mount for the particular application. Solid metal mounts are speciﬁcally prohibited. Any non-metallic inserts may be used. All components between the engine and the mounting structure are considered to be part of the motor mount assembly and therefore comprise the motor mount.

Other cars have 'urethane inserts' (which are legal per the rule above) available through the aftermarket that are basically the same thing, just pre-molded to fit the mount instead of poured. This is just making something that is not available for our cars.

Clod_King · Sep 26, 2011

This is cool. I cannot wait to hear how this goes.

samsavell · Sep 27, 2011

For 30 dollars, it sounds like a nice easy way to get your hands dirty and take care of a mod that needs to be done on this car! I'll be watching to find out what the vibration is like. That's always the deal breaker for me when it comes to motor mounts.

Also, 1.5 Liters of Fury should be the new Mazda2 catchphrase.

CorkSport · Sep 28, 2011

samsavell said:
Also, 1.5 Liters of Fury should be the new Mazda2 catchphrase.

Nice!

Richard_rsp · Sep 28, 2011

samsavell said:
Also, 1.5 Liters of Fury should be the new Mazda2 catchphrase.

(thumb)

DaleNixon · Sep 28, 2011

Awesome deal man. Let's get some driving impressions!

BRIAN_MP5T · Sep 28, 2011

Nice job.

Richard_rsp · Oct 4, 2011

ok, FINALLY got the mount installed tonight....

impressions? I can definitely tell it is not as stiff as the AWR mount, but there is basically NO NVH over stock (or at least what I remember of stock).... I have a feeling its gonna be wonderful for a daily driver! Stiffer than stock, but no vibration penalty! As of right now, 100% would do it again.... Kinda would be interested to see how the 80A durometer does... But I'll let someone else try that!

Slow Paul · Oct 4, 2011

This seems pretty easy to do. I might have to give that 80A a shot. But before I do.... where does one acquire the materiel?

Richard_rsp · Oct 4, 2011

http://www.mcmaster.com/

Part number 8644K24 is the 60A, but they have 80A too

Racebrewer · Oct 5, 2011

I believe that Energy Suspension also has the goo. I don't know how price compares.

Richard_rsp · Oct 6, 2011

Ok after 2 days, here is my latest impression:

1) There is VERY little vibration. I have noticed a slight increase (over stock) at idle. It is not bothering at all and is really only noticeable through the steering wheel.

2) Shifts are about the same or just slightly better than stock. I feel that the AWR mount really excelled in providing excellent shifting feel.

3) Engine movement is greatly reduced from stock. Alot of the 'jerkyness' from being on-off throttle has gone away! Should have been like this from the factory...

Overall, still very happy. I miss the crisp shifting feel of the AWR mount, but do not miss the vibration. Filling the stock mount seems to be an excellent 'mild' upgrade, perfect for a daily driver.

Mazdamatic · Oct 6, 2011

Richard_rsp said:
Ok after 2 days, here is my latest impression:

1) There is VERY little vibration. I have noticed a slight increase (over stock) at idle. It is not bothering at all and is really only noticeable through the steering wheel.

2) Shifts are about the same or just slightly better than stock. I feel that the AWR mount really excelled in providing excellent shifting feel.

3) Engine movement is greatly reduced from stock. Alot of the 'jerkyness' from being on-off throttle has gone away! Should have been like this from the factory...

Overall, still very happy. I miss the crisp shifting feel of the AWR mount, but do not miss the vibration. Filling the stock mount seems to be an excellent 'mild' upgrade, perfect for a daily driver.

time to patent that.

there should be a section just for threads on homemade stuff i love seeing what ppl come up with =]

Slow Paul · Oct 6, 2011

Richard_rsp said:
http://www.mcmaster.com/

Part number 8644K24 is the 60A, but they have 80A too

Thanks for this!!

Richard_rsp · Nov 13, 2011

Update: All is well! The mount is working great! Highly recommended!

The only additional thing I have noticed is that I will sometimes get a little more vibration on reversing, but it is minimal. ESPECIALLY when compared to the AWR mount.

Anybody else try this yet?

justanothermp5 · Nov 13, 2011

AWESOME! also just found they have 94A durometer, I have some extra mounts at my house, would be interesting to see how that would feel lol
I had no idea McMaster Carr sold stuff like that

skullsroad · May 22, 2012

So how much did the car vibrate with the AWR mount exactly? I'm assuming you went with the 70 durometer option?

I hate how this new car has turned me into a pansy. I came from a daily driven, completely gutted, 2000lb 1991 Sentra SE-R with urethane mounts, 400lb springs and a test pipe, and now I'm all worried about adding a smidgen of vibration to my M2. Oh my....

eyeballs · May 25, 2012

Anyone know what durometer equivalent the 3M window weld would be closest to? I've seen it used for filling mounts multiple times.

I've filled my rear motor mount!

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