First noted for use with MGA Twin Cam left side only. Can also be used for any MGA pushrod engine both sides, and any MGB 1962-1974 both sides. For a part drawing and more information, see part number listing AHH5896.htm

The MG Series MGA Twin Cam Workshop Manual describes this part in Section A.37, Modified Engine Mounting. "Commencing at Chassis No. MGA528, a packing plate (Part No. AHH5896), together with longer set screws (Part No. HZS0506), is fitted under the engine mounting on the left-hand side only. This packing plate is introduced to give an increased clearance between the starting dog (on the crankshaft pulley) and the steering rack housing. The modification can be fitted to chassis prior to the one given above".

Picture at right shows the crank dog nut when viewed from front below the air pan and above the steering rack, without the LH engine mount shim in place. This shim may reduce or prevent interference between the Starting Handle (hand crank) and top of the steering rack housing. It may also make changing the fan belt easier. It still may not allow removal of the crank dog nut when the required wrench socket may still not fit (even with the shim in place). Removal of the dog nut with engine in the car requires a wrench socket and impact wrench.

There is also a side note that the Twin Cam left side engine mount was given a different part number from the left mount on the pushrod engine cars. These parts are otherwise physically identical. I might speculate that it was originally intended for the Twin Cam part to have different durometer rubber, possibly to be a little stiffer for the heavier twin cam engine with more power (more torque). So far no one has produced the original factory drawings, so this may forever remain a mystery. Meanwhile, many of the replacement parts suppliers use a single part number to serve both pushrod and twin cam engines.

You might give some consideration to installing Heavy Duty engine mounts on the Twin Cam engine, although rubber durometer or stiffness specifications for these parts are seldom disclosed. There have been some comments to the effect that the Heavy Duty engine mounts may be "harsh", transmitting more vibration to the chassis. That may be okay for competition, maybe not so good for street use.