Next time you put your foot to the floor to accelerate away from a stop, or
motor on up an on-ramp, take a second to fully appreciate what's happening.
All the power created by the miracle of internal combustion going on inside
the engine is smoothly making it's way to the ground without the vehicle
rattling itself apart from vibration, or the engine twisting its way through
the hood. Despite the engine's best efforts to twist itself out of the engine
compartment, the process of acceleration is largely uneventful thanks to the
system of engine mounts holding the powerplant firmly in place.
One end of the system bolts to the engine, and the other end is secured to the
vehicle frame or sub-frame. Along with holding the engine in place, the engine
mounts have another equally important function: They also isolate the
surrounding steel from all the vibration and shaking going on as the engine
makes power. The engine mounts simultaneously hold things down and allow for
movement. Save for a few very fancy viscous fluid or hydraulic type systems,
most engine mounts accomplish this feat with just two metal parts bonded
together with a rubber insulator in between. The rubber holds the two metal
mounting points together, and also allows for a small amount of movement,
while absorbing engine vibration and preventing it from reaching the rest of
Wear and Tear
Just like tires, kick balls, floor mats, or anything else made of rubber that
takes a beating, engine mounts can also wear out and fail. Time and thousands
of stops and starts take their toll on the rubber holding the metal of the
engine mounts together. The rubber can crack, become spongy, or just plain
fall apart. Liquids leaking onto the mount itself will accelerate this
process. Oil, power steering, transmission fluid, or any other leaking liquid
falling down upon the engine mount will rapidly impel its demise.
Engine power modifications in conjunction with overly spirited driving can
also overcome the original design specifications of the engine mount and cause
torque induced engine mount failure. If, when you put the pedal to the metal,
there's a whole lot of shaking, thunking, and clunking coming from under the
hood, then it may be time to inspect and replace the engine mounts. If the
engine is small, a good two-handed push or heave-ho may reveal way too much
movement, and daylight shining through the two halves of the broken mount.
Larger engines will require a jack and various blocks of wood in order for you
to check for broken mounts. If a broken or cracked mount is found, chances are
the others have been overstressed and are on their way out as well. Also keep
in mind that, along with the usual two engine mounts, there is a third cousin,
the transmission mount. Follow along with the step-by-steps for some handy
tips for replacing engine mounts. Inspecting and replacing worn or broken
engine and transmission mounts will help the rubber meet the load.