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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).
Engine vibrations, causes, and tests with different pistons.

Identifier  ExFiles\Box 3\1\  01-page093
Date  19th August 1913 guessed
  
6.- I think that the fact of the engine being very securely bolted to the frame a certain amount transmits these excessive vibrations to the frame, and, therefore, to the B.G. Also that the 'in scuttle' and fittings do accentuate the vibrations.- This latter has been proved in Mr. Forthays car, where it was found by Mr. Hives that considerable improvement was made by the isolation of the scuttle and body from the chassis.

8.- I tested the car with the same pistons as were fitted when same was run by Mr. Royce. The question of detonation I have already answered under No.2. - I understand that the car has now been returned to Mr. Royce and there does not seem to have been any time for tests to be made with the light pistons of different shape, as suggested by Mr. Royce. I have always thought, however, that detonations from engines fitted with convex piston tops are worse than the concave type.

This vigorous engine vibration is more or less prevalent on all our cars which we are now turning out, and which are giving such excellent powers at slow speeds or soon develop so.

Anything which reduces the vigour of the explosion at such low speed improves matters. Although it gives less excellent power, acceleration, and efficiency. (petrol consumption etc.)

The following are a few features which reduce the "vibro".

a.{Mr Adams} Poor carburetion at slow engine speeds.

b. Abundance of carbon deposit. (I have tried to avoid cylinders being passed in which the walls of the cylinder are too thick. I believe this is one of the reasons why engines vary in this respect)

c. Piston rings being a poor fit and
  
  


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