If your car is feeling sloppy every time you shift or accelerate, a polyurethane motor mounts diy project might be exactly what you need to tighten things up without spending a fortune on aftermarket parts. Most factory engine mounts are made of soft rubber designed to prioritize comfort above everything else. While that's great for a daily driver that never sees a spirited corner, that rubber eventually cracks, sags, and turns into a mushy mess. When that happens, your engine starts rocking back and forth like a pendulum, which saps power and makes the car feel disconnected.
The alternative is buying "performance" mounts, but those can easily run you hundreds of dollars. That's where the DIY approach comes in. By using a two-part liquid polyurethane mix, you can basically "rebuild" your current mounts or fill the gaps in them to create a much stiffer, more durable setup. It's a messy job, sure, but it's incredibly satisfying and costs a fraction of the price of a name-brand replacement.
Why Even Bother With Polyurethane?
The big draw here is throttle response and shifting precision. When you hit the gas, the engine wants to twist. In a stock setup with soft or worn rubber, a good chunk of that initial energy goes into compressing the rubber mounts rather than turning the wheels. By switching to a stiffer material, you minimize that movement. This is especially noticeable in manual cars, where sloppy mounts can make it feel like the shifter is dancing around while you're trying to find third gear.
Polyurethane is also way more resistant to the chemicals found under the hood. Oil leaks, coolant spills, and road salt eat through rubber over time, but poly just shrugs it off. However, there is a trade-off: NVH (Noise, Vibration, and Harshness). Because the material is stiffer, it's going to transmit more engine vibration into the cabin. If you're building a track car, you won't care. If it's your mom's luxury sedan, she might not be thrilled when her rearview mirror starts blurring at stoplights.
Choosing the Right Shore Hardness
Before you start pouring anything, you have to decide how stiff you want to go. Polyurethane is measured on the Shore A scale. * 60A is roughly equivalent to a firm factory mount. It's a good choice for a daily driver where you want things a bit tighter but don't want your teeth to rattle. * 80A is the sweet spot for most enthusiasts. It's noticeably stiffer and offers great engine control, though you'll definitely feel more vibration at idle. * 94A and up is basically solid. This is for dedicated track builds or people who simply don't care about comfort.
Most people doing a polyurethane motor mounts diy fix tend to go with 80A. It provides that "connected" feeling without making the car unbearable to sit in during a traffic jam.
Getting Your Supplies Together
You don't need a massive shop to do this, but you do need some specific supplies. First and foremost, you need a two-part liquid polyurethane kit. Brands like Smooth-On (specifically their PMC series) are popular in the car community.
You'll also need: * Degreaser or brake cleaner: And lots of it. * Duct tape or heavy-duty masking tape: This is your "mold." * Mixing cups and stir sticks: Don't use your kitchenware; this stuff is toxic. * A heat gun or oven: Optional, but helps with curing. * Safety gear: Nitrile gloves and eye protection are non-negotiable.
Preparing the Mounts for the Pour
This is the most important part of the whole process. If your mounts are oily or dirty, the polyurethane won't bond to the rubber or the metal housing. It'll just peel out after a week of driving, and you'll have wasted your time.
If your mounts are completely shot—meaning the rubber has separated from the metal—you'll want to scrape out the loose bits. If you're just reinforcing "good" mounts that have large voids (common in many modern cars), you just need to get them surgically clean. I usually hit them with a wire brush first, then soak them in a strong degreaser, and finish off with several rounds of brake cleaner. You want that rubber to look dull and bone-dry.
Creating the Mold
Since you're pouring a liquid into a part that has holes in it, you have to create a "dam" so the poly doesn't just run out onto your workbench. This is where the tape comes in. You want to seal off one side of the mount completely.
Pro tip: Use high-quality duct tape and really press it into the edges of the metal. If there's even a tiny gap, the liquid poly will find it. It has the consistency of syrup when first mixed, and it will leak everywhere if you aren't careful. I usually build up a few layers of tape and then sit the mount in a tray of sand or on a flat piece of wood just in case a leak happens.
The Mixing and Pouring Process
Once you're taped up and leveled out, it's time to mix. These two-part kits usually go by weight or volume, so read the instructions carefully. If you get the ratio wrong, the poly might stay gooey forever or become brittle.
Mix slowly to avoid introducing too many air bubbles. Once it's a uniform color, pour it into the mount slowly. If the mount has deep crevices, you might want to poke around with a thin stick to make sure the liquid has filled every corner. Fill it right up to the brim, as the material might settle slightly as it cures.
The Waiting Game (Curing)
This is where most people mess up their polyurethane motor mounts diy project. You'll be tempted to toss them back in the car after a few hours because the surface feels firm. Don't do it.
Most liquid polyurethanes take at least 24 hours to reach an initial cure and up to a week to reach full strength at room temperature. If you put them in too early, the heat and weight of the engine will deform the material before it's ready. If you're in a hurry, you can sometimes "bake" the mounts in a toaster oven (not the one you use for food!) at a very low temperature to speed things up, but honestly, just letting them sit on a shelf for a couple of days is the safest bet.
Installation and the "Break-In" Period
When you finally bolt the mounts back into the car, don't be surprised if the vibrations feel intense for the first hundred miles or so. Polyurethane actually has a bit of a break-in period. As the material heat-cycles from the engine's warmth, it will settle in.
Check your bolts after a week of driving. Because the mount is stiffer now, it transmits more energy to the mounting hardware, and things can occasionally vibrate loose if they weren't torqued down properly.
Is it Worth the Effort?
Total cost for a project like this is usually under $50, assuming you already have basic tools. Compared to the $200-$400 you might spend on "pro" mounts, the value is insane. Plus, you get the bragging rights of having built them yourself.
A polyurethane motor mounts diy job isn't for everyone—if you want your car to feel like a cloud, stick to OEM rubber. But if you want to feel every bit of torque and get rid of that annoying engine flop, this is one of the best weekend projects you can tackle. Just be prepared for a little more vibration and a whole lot more fun behind the wheel.