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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).
Letter discussing engine bearing wear, oil pressure issues, and flywheel balance on a Bentley.

Identifier  ExFiles\Box 83\1\  scan0201
Date  19th September 1936
  
X200a

To I.M. Waller,
Hotel de France,
Chateauroux,
Indre, France.

We have received your telegram re oil temperatures. We think it is a mistake to test a bearing material without knowing what the oil temperatures are. It may save a connecting rod going to the bottom half. Have you no parts on the 25/30 which you could transfer to the Bentley ?

We want you to keep an eye on No.6 big end. Last time we ran Hall's metal bearings we had a big end failure at 10,000 miles, fitted new big ends, and shortly afterwards had a second failure. We attributed this to the wear which had taken place on the main bearings. We do not want you to smash the engine up.

In view of the fact that you have a good oil pressure you ought to be getting oil to the big ends unless the flywheel bearing has worn so badly that the oil escapes at this point and starves No.6 connecting rod. You could do a test by removing the bottom half and putting the crankshaft under pressure to see how much oil is coming out of No.6 bearing.

We were never able to substantiate that the main bearing wear on the last 15,000 miles car was anything like the figure suggested by G.W.H. We attach measurements taken by the shop after the unit was stripped. From this you will see that the greatest possible clearance on No.6 bearing was .006", whereas Hancock said .020". We do not know why No.6 bearing should wear more rapidly than the others, unless the flywheel is out of balance. Can you improve the balance on your engine by adding a small mass to the flywheel at any point ?

How much can you lift the flywheel on 22-G-V ?

We are sending out some better big end bearings to you, but if the trouble is due to oil shortage, they will not be much use. We want all the information you can give us.

Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}
  
  


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