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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).
Issues with the ignition advance governor, specifically friction, stiction, and clearance problems preventing full advance.

Identifier  ExFiles\Box 65\1\  scan0061
Date  23th January 1925 guessed
  
-2-

The net result of this negative torque,friction in the governor element, and stiction in the piston, is that ignition advance will not commence at 500 r.p.m. under the most favourable conditions. When the oil is cold or contains any impurity, the commencement of ignition advance is still further delayed.

In addition we consider it possible that the ignition might stick in the fully advanced position due to impurity in the oil. In this case the spring required to give the correct governor curve will exert a force of approximately 2.75 lbs. on the governor shaft. After allowing for friction it is doubtful whether the force available at the end of the lever operating the piston will attain 1 lb. We have had the piston stick so that it required more than 1 lb. to move it.

To eliminate this trouble we are having the inner piston made in brass with increased clearance.

We doubt whether we shall be able to reduce the ignition advance to commence before 600 r.p.m. with the present governor. We can get the end of the lever to advance at 500 r.p.m. when not connected to the piston, but it will not lift the piston.

(3) We cannot get the full 30° automatic advance required with the parts as at present made. We find we are losing a small amount of movement due to excessive clearance in the location of the long lever.

[Sketch of a lever]

Even when this is removed we shall barely get the required 30° contd.
  
  


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