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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).
Meeting notes discussing crankshaft bearing failures on 4¼ litre Bentley engines and proposed modifications.

Identifier  ExFiles\Box 114\3\  scan0098
Date  10th December 1936
  
Hs.{Lord Ernest Hives - Chair}
C. by.{R.W. Bailey - Chief Engineer} Rm.{William Robotham - Chief Engineer} Hl. Da.{Bernard Day - Chassis Design}
Rm{William Robotham - Chief Engineer}/CWH. /JNR{Charles L. Jenner}
E.4/HP.10.12.36.

Bentley Crankshaft Bearings.

The following notes were taken at a meeting held to discuss the Bentley crankshaft and connecting rod bearing position. Hs.{Lord Ernest Hives - Chair} Ry. Rm.{William Robotham - Chief Engineer} E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design} Hl. Rm{William Robotham - Chief Engineer}/CWH and E/JNR{Charles L. Jenner} present.

In view of the two failures which have occurred recently on 4¼ litre Bentleys, one after only a short mileage, it is decided that some more urgent action and further modification will be required on production, and that retrospective action will also be necessary.

Rm.{William Robotham - Chief Engineer} has now got an effective test, reproducing it is thought the conditions under which failure occurs, and under this test RR.56 forged big-end bushes are still running at 15 hours, when the present standard cast Hall's metal bushes have failed in three hours.

The value of an improved oil feed to the crankshaft whereby the intermediate bearings are provided with wider grooves and the crank with two holes had also been demonstrated and tested.

To safeguard the oil feed to the big-ends by keeping down crankshaft main bearing wear to the minimum it is also proposed to fit a high pressure oil filter of the Tecalemit type; a similar one to those used on our Tank engines has already been tried with satisfactory results.

It will be necessary to change the filtering element at 5000 miles from new for the first time, and thereafter every 10,000 miles.

A larger oil pump has already been instructed for standardisation.

It is not proposed to change the material of the main bearings, but one development in connection with these is to use die cast bearings which have a finer grain structure, and
  
  


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