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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical memo discussing the design and performance of rubber engine mountings.

Identifier  ExFiles\Box 55\4\  Scan325
Date  7th March 1929
  
X7005

OY. from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}

Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}2/LG7.3.29.

RE. RUBBER ENGINE MOUNTING.

With reference to your OY12/15.2.29.

(1)
The engine weight may cause the side channels of the frame to deflect slightly due to the overhang of 1" in the bracket carrying the rubber, but this is not very noticeable even on the bump, and we have never experienced any ill effects from this cause. The steel plates we finally standardised will run 100 hrs. on our bump test without failing. We have never heard of one giving trouble in service. We used two 19 S.W.G. spring steel plates top and bottom instead of the single plate originally instructed.

(2)
Experimentally we mounted the rear of the engine .025" high to allow for any sag due to the slight permanent set of the rubber which inevitably takes place. On production this has been increased to .040" as they prefer the engine to be on the high side.

The rubbers being opposed, like the side steering tube springs, when the engine load is applied the lower rubber deflects about .012 depending exactly on the quality of rubber used. Therefore if the engine was lined up with solid aluminium distance pieces in place of rubber, it would actually be mounted .052" high to obtain the best results.

(3)
We can definitely say that there is no increase in the tendency to shimmy due to the reduction in

contd :-
  
  


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