Quote:
Originally Posted by cts-v
Since the matched set of 350 eng/frame or 455 eng/frame mounts place the centerline in the same place, why did Oldsmobile use 2 different mount designs? Different isolation characteristics (different damping rates) or for clearance issues? Or something else?
|
Actually, prior to the 1969 model year, there was only one design. The rubber mount design at that time was essentially two flat plates (with bolt flanges) with a chunk of rubber molded in between. The rubber eventually fractured, resulting in the engine torquing over and a jammed throttle. There was a major recall wherein GM added a steel cable torque strap from one of the exhaust manifold bolts to the upper control arm cross shaft.
To prevent this problem, Olds redesigned the rubber motor mounts so that the two metal parts actually interlocked. This way, if the rubber failed, the interlocking metal parts prevented the motor from torquing over. Note that GM also switched from a rigid throttle rod to a flexible cable, so that if the engine did move, the linkage wouldn't jam.
This redesign was rolled in over time. Olds started with the high-torque big block motors, so for the 1969 model year the 350 motor used the old design mounts and the 400/455 motors used the new design. The interlocking feature required the rubber mount to be physically larger, so the frame bracket was redesigned to accommodate it while not changing the location of the engine.
Starting in 1970, the 350 mounts were also redesigned to incorporate the interlocking feature, but apparently the engineers got smarter, as they were able to package the redesign in the original space.