Modifications to the Rolls-Royce flywheel and clutch
In order to overcome the problems inherent in the Rolls-Royce clutch as described, the Borg and Beck clutch was adopted and fitted to Derby Bentley 4 1/4L and 25/30 engines. We have created a modified clutch to fit to engines with the later Rolls-Royce clutch, including the Bentley 3 1/2L, with some of the advantages of the Borg and Beck design. The modifications include the following:
1 The friction linings which in the Rolls-Royce clutch are mounted on the flywheel and sliding pressure ring are transferred to the centre steel plate, as in the Borg and Beck design. See GD146 and GD215.
2 The plate mounted on the back of the flywheel that carried the friction lining is replaced with a solid plate GD255.
3 The original sliding pressure ring is replaced with a new sliding ring without the friction lining GD273.
4 In this modified design of the Rolls-Royce clutch the friction linings fitted to the central disc work against the replacement flywheel plate GD255 and sliding pressure ring GD273.
As well as the Bentley 3 1/2L (chassis series A-D) the modified design is available for 20/25 cars from chassis number GSY33 on. Prior to that point the sliding pressure ring had a different configuration of external splines which are not compatible with the later design.
Additional enhancements:
The flywheel of the original Rolls-Royce was effectively a sealed space within which the clutch was housed. One of the reasons for this was to limit the possibility of oil reaching the clutch, but it had the disadvantage of not allowing any airflow over the clutch, unlike the well-ventilated Borg and Beck design. The cooling effect of the airflow is significant, particularly when the clutch is working.
A further modification to improve the life of the Rolls-Royce clutch is to machine ventilation ports in the outside diameter of the flywheel to allow cooling airflow over the clutch. It is very unusual for there to be oil contamination in the clutch bell housing and on the flywheel, and the risk of the clutch becoming contaminated with oil as a result of creating apertures in the flywheel is very low. Oil contamination of the ventilated Borg and Beck clutch is extremely rare.
Modification of the flywheel can only be done with the flywheel removed from the engine.