If your car feels like it's trying to shake itself apart every time you hit the gas, it might be time to look into making some diy polyurethane engine mounts. Most factory mounts are made of soft rubber designed to keep the cabin quiet and comfortable, but as they age, they turn into mush. When that happens, your engine starts flopping around like a fish out of water, which kills your throttle response and makes gear shifts feel vague. Instead of shelling out hundreds of dollars for "performance" brand-name mounts, you can actually build your own using liquid urethane for a fraction of the cost.
Why skip the rubber and go for poly?
Stock rubber mounts are a compromise. Car manufacturers want the average driver to feel absolutely nothing through the steering wheel or seat, so they use rubber that's soft enough to absorb every tiny vibration. The problem is that soft rubber tears easily under stress, especially if you've added a bit more power to your car. When you switch to diy polyurethane engine mounts, you're essentially choosing a material that is much more durable and rigid.
Polyurethane doesn't perish as easily when it gets hit with oil or road salt, and it keeps the engine "locked" in place. This means when you step on the pedal, the energy goes to the wheels instead of being wasted as the engine twists in the bay. The downside? You're going to feel more of the engine. If you hate vibrations at a red light, this might not be for you. But if you want a car that feels connected and mechanical, it's a total game-changer.
Picking the right hardness for your build
Before you go out and buy a bucket of liquid urethane, you need to understand Shore hardness. This is the scale used to measure how stiff the material is. For diy polyurethane engine mounts, you're usually looking at three main levels: 60A, 80A, and 94A.
60A: The Daily Driver
This is the softest stuff you'd realistically use. It's firmer than stock rubber but still has enough give to keep your teeth from rattling out of your head. It's perfect if you just want to fix a broken mount without making the car feel like a vibrator.
80A: The Street/Track Compromise
This is the "sweet spot" for most enthusiasts. It's stiff enough to significantly improve handling and shifting, but it's not totally unbearable for a long drive. You'll definitely notice more noise, vibration, and harshness (NVH), but it's manageable.
94A: The Track Monster
This stuff is basically plastic. If you're building a dedicated drift car or a drag racer, go for it. If you're planning on taking your significant other out to dinner in this car, maybe skip it. At this hardness, the engine is practically bolted to the chassis with no dampening at all.
Preparing your old mounts for the pour
You can't just pour liquid urethane over a greasy old mount and expect it to stick. Prep is about 90% of the work here. First, you need to get the old mounts out of the car, which is usually the most frustrating part of the job—especially on transverse-mounted engines where one bolt always seems to be hidden behind the frame rail.
Once they're out, you have two choices. You can either "window weld" them (filling the gaps in the existing rubber) or completely gut them. For a proper set of diy polyurethane engine mounts, gutting them is the way to go. You can use a torch to smell up the neighborhood and burn the rubber out, or use a hole saw and a wire wheel to scrape it clean. You want to get down to the bare metal of the outer shell and the center pin.
Cleaning and Sanding
After the rubber is gone, hit the inside of the shell and the outside of the center pin with some heavy-grit sandpaper. Polyurethane needs a "tooth" to grab onto. If the metal is smooth and greasy, the poly will eventually just pop out like a cork. Use a heavy degreaser or brake cleaner to remove every last trace of oil. If it's not clean enough to eat off of, it's not clean enough to pour.
The sealing and pouring process
This is where things can get messy if you aren't careful. You need to create a "mold" so the liquid doesn't just run out the bottom. Most people use high-quality duct tape or heavy-duty packaging tape.
Lay the mount flat on a piece of wood or a workbench covered in plastic. Center the inner pin exactly where it needs to be—this is crucial because if it's crooked, your engine won't line up when you try to bolt it back in. Some guys use cardboard spacers or even 3D-printed jigs to keep everything centered. Wrap the tape tightly around the bottom and sides to create a leak-proof bucket.
Mixing the Urethane
Most liquid poly comes in two parts. You have to mix them exactly according to the instructions. If you eyeball it, the mount might never cure, leaving you with a sticky, gooey mess that you'll have to scrape out with a spoon. Mix it slowly to avoid introducing air bubbles. Bubbles are the enemy; they create weak spots in the mount that can lead to cracking later on.
The Pour
Pour the mixture slowly into one spot and let it flow naturally into the gaps. If you see air bubbles rising to the top, you can hit them with a quick burst from a butane torch or a heat gun to pop them. Fill it right up to the brim, maybe even a tiny bit over, because it might shrink slightly as it sets.
The waiting game (Curing)
Patience is the hardest part of making diy polyurethane engine mounts. Most of these kits require at least 24 hours to reach a "handling" strength, but they don't fully cure for several days. If you throw them in the car after six hours because you need to go to work, you're going to squish the soft centers and ruin all your hard work.
Keep them in a warm, dry place. If it's winter and your garage is freezing, bring them inside (maybe hide them from anyone who doesn't want the house smelling like chemicals). Heat helps the curing process, so some people put them in a low-temp toaster oven, but that's a risky move if you value your kitchen appliances.
What to expect on the first drive
Once everything is cured and bolted back into the car, the first thing you'll notice when you turn the key is the vibration. Your dashboard might rattle, and your rear-view mirror might get a little blurry at idle. Don't panic—this is normal. Polyurethane mounts usually have a "break-in" period where they soften up just a tiny bit after a few heat cycles.
The real magic happens when you actually start driving. The car will feel much more "mechanical." When you lift off the throttle, the car won't jerk as much, and when you slam it into second gear, the power delivery will feel instant. It's one of those modifications that doesn't add horsepower on paper, but it makes the car feel five years younger and much more aggressive.
Making your own diy polyurethane engine mounts is a messy, smelly, and time-consuming project, but the results are worth it. You get a custom-tuned feel for your car without the "tuner tax" associated with aftermarket parts. Just make sure you seal that tape well, or you'll be cleaning expensive goop off your garage floor for a week.