View Full Version : DIY: Polyurethane filled stock motor mounts

08-19-2002, 09:08 PM
I recently had an issue with my motor mounts that caused some serious problems for me. Previously I had the ES MM inserts. Well, they eventually wore out and my stock front motor mount was torn. This allowed a lot of extra play which led to vibration that knocked my front motor mount bolt loose. So then one fine day after a hard 2-3 shift, the engine rocks back so hard that it pulls off the lower radiator hose! :o As you might imagine, it wasn't a pleasant feeling to hear a THUNK as the valve cover hit the underside of my seibon hood, and then, seeing a cloud of white vapor ensuring a safe getaway from any potential pursuers.

Anyhow, I hate paying excess prices for things I can do myself so I started looking into polyurethane mixes with which I could "rebuild" my stock motor mounts. Because hey, the brackets were just fine, AND they're cast aluminum so they're strong and light.

Lo and behold, I came across some polyurethane products that looked like they'd work. So yesterday I rebuilt my stock mounts to what is essentially race mount hardness using the stock mounts. I doubt most people would want their mounts as firm as I have, but there are softer polyurethane products that will work and have more give.

I thought about using the tried and true "window weld" fix, but the cure time on it was kind of ridiculous. I settled on some 3m 2 part poly urethane mixes. It's part of their "Scotch-weld" lineup of products. These products certainly weren't cheap (they required the purchase of a rather expensive applicator gun AND you have to use a new disposable nozzle for each bottle of stuff you use), but they had really short cure times AND were much firmer than window weld. For reference, window weld has a hardness of 55A and the products I used had a hardness of 70D and 85A respectively.

The front mount I wanted to be basically solid with very little give at all. I used the 3M DP601-NS product. This stuff is HARD. It's a polyurethane, so it won't crack, and it has an adhesive strength of 2000+psi. Anyhow, the NS means "no sag" which means that it comes out thick and won't run. They also sell a self leveling version of the product which comes out looking a little nicer, but it's harder to work with. Anyhow, here's how the front mount looked after I was done.


I just filled the holes in the stock rubber mount (as well as putting some inbetween the two parts that tore). This mount cured fully in about an hour. You have to be very careful when putting the mount back on the car b/c the mount is solid, everything has to line up really well b/c you can't flex the mount into place like with the stock stuff.

For the rear mount, I did something a little unique. I wanted the mount to be as firm as possible, but I also wanted some give so that the idle was reasonable. The solution was to use the ultra-firm stuff on the top, and the softer stuff on the bottom. The softer mix is the DP604-NS. This stuff is rated to 900psi and cures in 6 hours. The great thing about these mixes is that they don't require heat or application in thin layers to cure all the way. It's a 2 part chemical reaction that occurs so you fill the whole mount in a single step.


I coated the whole outside with the black stuff just so it looked a little better. In the future I'll be able to make these a LOT prettier. I was pressed for time so I didn't get to make it look pretty by leveling with a spatula or something.

So the final result - these mounts are FIRM. There is still some give b/c the stock rubber is still inside. As a result, Idle didn't change much from when I had just the ES MM inserts. There is more vibration at low rpm between 2000-2500rpm. Highway cruising is about the same as before.

When I step on the gas with these mounts, there is zero hesitation. The car just gets up and GOES. The power goes into turning the wheels, not into compressing the mounts.

Oh, here's what my ES MM insert looked like after about 90k miles


It was destroyed. For anyone that drives agressively, this is definitely the low cost alternative for buying full new mounts. I wouldn't really reccomend that anyone use the gray stuff unless they're hardcore like me, but the black stuff is a good product and it will turn your mounts into the equivalent of a solid polyurethane mount.

The most expensive part of this was buying the mixer gun. How could something so tiny cost so much. :(


Here's the used containers. If it wasn't for that gun and the rush shipping I paid, I could have easily done both mounts for under $70. Not bad considering how much new polyurethane mounts go for. My front is actually stiffer than just about anything that is commercially availible.

On the bright side, if I ever have to do it again, I can do it for cheap. Oh, and there is no wheel hop. whatsoever. at all. :mgrin:


03-30-2011, 07:11 AM
Thought some of you DIY'ers and other individuals may appreciate a bump in this thread.

03-30-2011, 10:54 PM
Ive always been curious about doing this, glad to see that it worked out for you, I may have to try this one day, both my front AND rear mount are torn but I got ESMM's cuz I'm cheap :mbiggrin: Thanks for the DIY!

04-14-2011, 09:26 AM
how did he blow through 90k miles and broken motor mounts within a year?

06-30-2011, 09:35 PM
Anyone know where I can get the applicator gun??

07-01-2011, 10:56 AM
Anyone know where I can get the applicator gun??

They make solid motor mounts for the ep3 now

doing it like this is like putting a band aid on the spot where your arm used to be after it was torn off...

07-01-2011, 11:28 AM
Don't wanna sound like an ass, but I already knew that. A buddy of mine wants to try this, and he can't find that mixing gun. Thanks for your help though.