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).
Fracture of a fibre pad on the low tension rocker arm, its potential causes, and proposed design modifications.
| Identifier | ExFiles\Box 89\1\ scan0229 | |
| Date | 6th January 1938 | |
| CHILDS BY.15/G.6.1.38. 261 CHASSIS NO. B.56-GA. E.F. SUMMERS. RE: FRACTURE OF FIBRE PAD ON THE LOW TENSION ROCKER ARM. Referring to Sg.{Arthur F. Sidgreaves - MD}2/E.5.1.38, the form of pad which we are using has been in service for three years (since 1934). It is formed by pressing together linen material, soaked with Bakelite resin, and baking same. We have had four failures of this type up to date. In examining the particular failure under discussion it is evident that the face of the fibreblock is worn at a slight angle, and this has increased the impact. Possibly, at the same time, judging by the colour of the piece it may have been somewhat over-baked in the final 'curing' or 'stabilising' of the material. The heating process is necessary to change the glue-like Bakelite resin into the hard compound which is used, into its final hard condition, such as one sees in, for instance, the distributor cover, casing for the ignition, and the boxes etc. one sees moulded in Bakelite. I do not feel that we are likely to have an epidemic of this type of failure, it only occurs after considerable mileage, and then I am inclined to think it will be confined to a few cars where the engine revv. runs up towards the maximum allowable. So far we have had three failures on Bentley and one on the 25/30. I am modifying the design to give an increased 'heel' to the block, in order to take the blow in compression instead of tension. Incidentally the Phantom lll has the block reversed and should be from this point of view immune from the trouble. BY.{R.W. Bailey - Chief Engineer} | ||