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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).
From Wellworthy Piston Rings Ltd. detailing recommended working clearances and nip for connecting rod and main bearings.

Identifier  ExFiles\Box 115\5\  scan0079
Date  7th July 1938 guessed
  
W.EES/RB{R. Bowen}

diameter greater than the diameter of the housing into which its fits. The figure we usually work to is 0.0005/inch diameter.

Nip of Bearings in Housing.

By nip of bearing, we mean the amount by which the bearing halves stand proud of the joint face. This should be 0.001" on each side of the bearing relative to the joint face for each half of bearing.

Working Clearance.

We recommend the following clearances for bearings -

(a) CONNECTING ROD BEARINGS.

For connecting rods we find the following clearances satisfactory -

Minimum - 0.001"/inch diameter.
Maximum - 0.0015"/inch diameter.

(b) MAIN BEARINGS.

For main bearings where crankcase and crankshaft distortion must be taken into account, we find that the following clearances are necessary -

Minimum - 0.0012/inch diameter.
Maximum - 0.00155/inch diameter.
Preferred - 0.00135/inch diameter.

We trust that this information will prove of interest to you and if there is any further help we can give you please let us know.

Assuring you of our fullest co-operation and service at all times,

Yours faithfully,
For WELLWORTHY PISTON RINGS LTD.,

Technical Manager.
  
  


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