Service Manual

ISB, ISBe and QSB (Common Rail [...] Engine Mounts
Section 16 - Mounting Adaptations - Group 16 Page 16-47
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system is close to the frequency of the engine vibration. This can result in the mounting system operating at or near
resonance, with a resulting magnification of the input vibration. This is obviously an undesirable situation.
Transmissibility values of less than one indicate the mounting system is transmitting only a fraction of the vibration
input from the engine, thus isolating the vehicle from engine vibration. Good engine mounts will reduce the amount of
engine vibration transmitted to the chassis frame by at least 50 percent at idle.
Stiffness (durometer) and size of the isolator, along with the weight of the engine or component applied, are the
determining factors when designing a mounting system. An isolator that is correct for one engine may not be right for
another. Likewise, because of weight differential, a particular isolator designed for the rear of an engine probably will
not be ideal for the front. Hard engine mounts will give little or no isolation, and can actually magnify the vibration
transmitted to the chassis.
The following are illustrations of typical FRONT engine mounts.
1 Bolt
2 Supported member
3 Snubbing washer (or flat bracket surface of equal diameter
4 Rebound tail
5 Bonded metal center
6 Locknut
7 Supporting member
8 Rubber mount.
The following are illustrations of typical REAR engine mounts.