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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).
Analysis of the failure of the No.1 Big End bearing for chassis B.238-CA.

Identifier  ExFiles\Box 114\3\  scan0161
Date  22th December 1937
  
RM{William Robotham - Chief Engineer}/GWH.{George W. Hancock - Head Chateauroux}
c. PHC/Mr.Goodall
C. BY/NS.{Norman Scott}

CHASSIS NO. B.238-CA. H.{Arthur M. Hanbury - Head Complaints} PEAKE.
RE: FAILURE OF NO.1 BIG END.

I have examined the pieces of the bearing which Hd.{Mr Hayward/Mr Huddy} submitted to me and it is quite clear from same that the big end failure was due to insufficient lubrication.

From enquiries made it is clear that there was no obstruction in the oil ways, and the reason for poor lubrication must therefore be looked for in a different direction.

In examining the fractured bearing, it was clear that it had broken completely across in three places, the lines of fracture being parallel to the axis of the crankpin. The failures had started from the outer edge of the flange and worked inwards and across the bearing. The reason for this in my opinion being that the rod was built with insufficient nip in the first place. This is a fault which has been recognised and cured (by instructing .002 of nip). The absence of nip, apparently in conjunction with a rod on the upper side of the limit has resulted in it being possible to bend the big end of the rod, and through the rod the bearing. Whilst the rod would stand the flexing the bearing would not, owing to its very considerable lower modulus of elasticity. This resulted in cracking being started from the flanges inwards, the cracks worked across the bearing, and when due to movement the cracks were worn to a certain dimension, oil was allowed to escape via the three cracks, leaving the pin itself short of lubrication.

The above emphasizes the need for the .002 nip which has recently been instructed for the aluminium bearing material on both main bearings and big ends.

BY.{R.W. Bailey - Chief Engineer}
  
  


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