engine shock mount SDR

[SteveG]

I recently undertook what at first appeared to be the straight forward task of replacing the rear engine shock mounts on an A model. But, as usual, the job goes south pretty quickly. The problem first manifested itself as not being able to torque the thru-bolt to the specified value without the nut just bottoming out on the last thread. Pulling it back off and inspecting to understand the problem it becomes apparent that the shock mount, part no. J-9613-31 by Lord, does not fit the application. The mount's design is intended to have the flange surface of the two halves meet in the middle of the engine mount spacer and the internal spacer mate with the upper and lower shock mount components once the assembly has been compressed to the proper preload. But in my instance the engine mount spacer plus the mounting plate is too thick to allow either of these parameters to be met. The removed parts are the same as the new so this aircraft has not had, for at least the last twenty years that I'm familiar with, a properly fitting shock mount. I believe this leads to premature failure, which at the usurious price of $300 each is undesirable, along with engine sagging misalignment and increased vibration being transmitted into the airframe and the resulting noise and stress fractures.

So, my questions to you all are: has anyone else previously identified this problem and if so how was it dealt with? how widespread is this condition? do other models have a different configuration or are we all operating with misfit shock mounts? are other make & model aircraft involved?

I've been corresponding with the product engineers at Lord but so far they have just said "we're looking into it". I "fixed" the problem by inserting an additional spacer between the mount halves and adding washers to the internal spacer to make up the gap. I'd be most interested to have feedback from other operators concerning this matter. It's hard to comprehend how the correct part no. does not fit the application.

Regards, Steve G.