What Are Motor Mounts?

The internal combustion engine is a rotating mass of several hundred pounds of parts, so vibrations are to be expected. Thanks to some specialized hardware, though, most drivers barely notice them. Engine mounts, also called motor mounts, absorb or neutralize these vibrations and decrease shift shock.

Motor Mount Design: The Basics

Motor mount design varies, depending on the weight and force it supports and how much vibration it transmits to the rest of the vehicle, but the simplest engine mount is basically a piece of rubber sandwiched between pieces of metal. One side is fixed to the frame of the vehicle, the other side to the engine.

There are a few different types of motor mounts:

• Rubber mounts are relatively simple. A time-tested design, they’re usually found on older vehicles, economy cars and work vehicles.
• Stiffer polyurethane mounts don’t absorb as much vibration but are stronger for certain scenarios, like track days or off-roading. They’re usually found on sports cars and are available as an upgrade for many vehicles.
• Some engine mounts may be filled with fluid to further decrease vibration. These are usually found on mid range sedans and luxury cars.
• Active mounts may be controlled electronically or by a vacuum to absorb specific frequencies or counteract shift shock.
• Some mounts look like tiny shock absorbers. They allow more engine movement and vibration damping.

Motor Mount Failure: Cause and Effect

Engine mounts wear out over time. Heat, oxygen and ozone exposure cause the rubber to stiffen, reducing their ability to dampen vibrations. So, if you feel more engine vibration, your engine mounts might be stiffening.

Eventually, stiffer engine mounts may crack, and oil leaks may further weaken cracked rubber mounts. The excess engine movement caused by cracked mounts can lead to serious problems, such as damage to the intake, exhaust, hoses or wiring.

In extreme cases, an engine mount may break. Depending on its design, the engine might hang loose or simply move more than it should when a motor mount breaks. A broken engine mount may knock or clunk on acceleration or during upshifting, downshifting or when braking. A few potential effects of broken engine mounts include crushed oil filters, popped constant velocity axles, ripped radiator hoses and crushed AC compressor clutches.

Replacing Motor Mounts

There are a couple of ways to replace a motor mount. If the engine mount isn’t load-bearing, it’s usually a simple matter of unbolting the old and bolting in the new. For load-bearing motor mounts, a small jack or engine support bar will be needed to lift the engine.

Replacing a broken motor mount may not be a simple repair, though, especially in many of today’s claustrophobic engine compartments. You may need to remove or loosen several other components to access the motor mount and remove it from the vehicle. Be sure to reinstall everything in the reverse order of removal. While you’re there, don’t forget to check other mounts for wear and tear, such as transmission mounts and differential mounts.

Although engine mounts aren’t replaced often, the average DIYer should be able to get the job done with a decent set of tools. If you don’t have a way to reliably support a heavy engine or you need to access the motor mount from below, it might best be left to your local NAPA AutoCare experts.

Check out all the engine parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on motor mounts, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

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