Motor mounts need to be replaced when the rubber bushing becomes dried, hard or begins to deteriorate after supporting the weight and vibration the engine produces over time. A car's engine is suspended in the engine bay and supported by connecting brackets secured to the car's frame. Between the brackets and the frame are large rubber bushings used to dampen the tremendous vibrations from the engine and to protect the car's frame from being damaged by the motor's torque on startup and acceleration.
When the motor mounts start to deteriorate, the engine will idle rough. Starting the engine will be noticeably more obtrusive for the car's occupants. When the engine starts and the crankshaft turns one way, the initial momentum wants to make the engine go the other direction. The motor mounts absorb this tendency and make the ignition sequence smooth and quiet. When the bushings fail this process is noisier and more noticeable.
The motor mounts are located differently on most model cars. Models of a particular manufacturer (GM, Ford, Toyota, etc.) may share the same type engine and will have the motor mounts in the same locations. The best place to look is at each "corner" of the motor. This may be in front, on or behind where the wheel well protrudes into the engine compartment. Once located, determine the access to the mount straight down with a socket wrench.
There is no need to remove the motor to replace the motor mounts. An engine hoist, however, or some other overhead lift, will help. When the old mount is removed the engine will want to lower into place. Avoid this by either holding the engine overhead or propping the engine motor bracket in place. If the model car or truck has enough clearance, a jack stand raised to the correct height will prevent the engine from lowering.
Use the appropriate socket to remove the motor mount bolt. Pull the old bushing from between the bracket and the frame. Replace with a new bushing and install the motor mount bolt.
One thing to remember, however, is the old bushing is probably crushed and allowed the motor to lower to a point where a new, taller bushing won't fit in the available space. When using a hoist, prop or jack stand to hold the motor, try to lift the engine a few millimeters. This will allow plenty of clearance to extract the old bushing and install the new.
