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Urethane Filled Mounts

If you want to stiffen up your motor mounts, then you have a few choices. The popular choices are to buy inserts or fill them with 3M WindoWeld. Inserts are easy to install, but can partially squish out of the mount under heavy load. 3M WindoWeld won't squish out, but takes a long time to apply. It is an air cured adhesive, so you have to apply it in thin layers. Each layer will take a couple hours to dry. One mount could become an all day affair.

So what else works? Industrial suppliers, like McMaster Carr, carry a variety of urethane adhesives. In this case, we are using a general purpose black urethane. That is part number 7493A35. You may need 1 to 2 packages, depending on the size of the mount. Always buy one more package than you think you will need, just to make sure you don't run out. The adhesive is a 2 part mixture and cures in 5 minutes. This one is a good choice because of its quick set time, flexibility, and good adhesion to rubber. The 2 part mixture is critical because it cures by a chemical reaction between the resin and hardener, not air drying. This means that you can apply it as thick as you want and finish the job quickly.

Get to work

You'll obviously have to remove the motor mount before filling it. This article won't go into that, as it covers any motor mount. You will want to follow the factory shop manual and proper safety procedure to remove the mount.

Once you have the motor mount in hand, you need to clean it. First clean it with a brush and dish soap. You just want to get the major dirt off. Now hit it with some engine degreaser. Let that soak and then towel that off. Now wash it repeatedly with dish soap. Keep washing it and drying it until you can't rub anymore black off of the rubber. A clean surface will help the adhesive bond to the rubber. Now you need to tape the holes in the mount closed. That lets you fill one side of the mount at a time. Otherwise the adhesive will just run out the back.

Now prepare your supplies. A board wrapped in aluminum foil works well for mixing on. You want a mixing board that won't soak up any of the hardener. The body filler spreader is good for mixing the resin and hardener. It lets you spread the mixture back and forth without adding air bubbles. The mixing sticks are needed as a helping hand while filling the mount. One package of adhesive includes 10 envelopes of hardener and resin. You will need 5-10 envelopes for each side of the mount (depending on the size of the mount).

You will want to separate and cut open 5 sets of resin and hardener envelopes. Squeeze out all 5 of the resins in one pool. Then squeeze out all 5 of the hardeners in a pool nearby. You can use a mixing stick to squeeze the last drops out of each envelope. Use the spreader to fold the hardener into the resin. Work quickly, but try not to entrain any air bubbles in the mixture. Use the mixing sticks to work the mixture into the mount. If this side of the mount is not full yet, open a few more envelopes to finish it off. Let it cure for 20 minutes or so.

Now peel the tape out of the back side of the mount. Notice how it has kept the adhesive from running through to the other side of the mount. A pair of needle-nose pliers may help peel out the stubborn bits.

Now cut open the final 5 sets of resin and hardener envelopes. Mix and apply as before. Use a few more envelopes if you need them. Let it cure for an hour in a warm place. An oven running at 200F is a decent choice for speeding the curing process. Follow the factory manual and proper safety procedure to reinstall the mount.

And that did what now?

If you did the front roll stopper or side mounts, you probably won't notice any vibration. If you did the rear mount, you may notice some more vibration. The urethane is pretty flexible, so it is a good compromise between support and comfort. At the very least, you have provided increased support for your engine and transmission. This is most important when you launch or accelerate hard.

Contributed by Corbin

Cars Modifications Power Motor_Mounts Urethane Filled Mounts

Document statistics: Last modified on 2009-01-02 23:25:53 by Corbin

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