Solid/Stiffened Engine Mounts With Window Weld
While removing the engine mounts for this upgrade, I noticed that the front mount had a bolt through it that was two sizes too small. I purchased a replacement bolt that perfectly fit the mount. There were never any problems and the car felt much more solid after these engine mount modifications. You can see how much larger the hole in the front mount is compared to the rear mount. Even though they both use the same size mounting bolt.
Clean the engine mount thoroughly with soap and water. After it has dried, apply the Windo-Weld to fill the rubber portion.
Verify that they are clean and dry, then proceed.
Try to not fill too much at a time. Allow inner layers to partially dry before applying more Window Weld. This will drastically reduce the time it takes for the mounts to harden and be ready to use.
Smooth the Window Weld if you want the mounts to look nice. You can use your fingers and deal with it taking a week to come off, use gloves, or use plastic rap to get a nice smooth finish.
Let the finished product dry for at least a couple days. Longer if you filled a large section in a single pass.
Moderate filling such as this transmitted a noticable amount of vibration into the passenger compartment and steering wheel. For a daily driver, we would recommend that you fill them according to the amount of power your engine now has. Do not completely fill your mounts unless you plan to go past 200 horsepower in the near future. The additional vibrations will eventually rattle interior panels loose and annoy passengers/significant others. You have been warned.
There are stiffer/stronger products out there for more money. Window Weld is perfect for most applications. Before spending more on a "better" engine mount reinforcement, please re-read the previous warning. If you just need to move to the next level, remove all of the rubber from the mount and completely fill it with Window Weld, reusing the center metal bushing.
If you want an even more solid engine mount, search for 80 to 90 shore durometer Polyurethane. It usually costs much more and can be more messy to work with, if that is possible.
For reference, the left mount is a 4th generation Mirage rear engine mount (roll stop) and the right one is the front one.