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).
The weights and clearances for new Bentley RR.56 connecting rods.
| Identifier | ExFiles\Box 85\3\ scan0059 | |
| Date | 11th October 1933 | |
| To Hs.{Lord Ernest Hives - Chair} from RHC.{R. H. Coverley - Production Engineer} X214 RHC.{R. H. Coverley - Production Engineer}9/BE11.10.33. BENTLEY RR.56. CONNECTING RODS Attached are particulars of weights for the Bentley Connecting Rods which have been forged in RR.56 material(produced by Hughes Johnson) and are of the drilled to provide lubrication to the small end. There is a reduction in weight of .483 lbs. compared with the Standard Bentley Connecting Rods. The increased section of rod(as shewn) gives ample clearance between pistons and cylinder skirt. It is intended to run the connecting rods direct on the crankshaft without the separate whitemetal bearing and also deleting the small end bronze bush. Therefore, in order to determine the correct bearing clearances, tests have been carried out to ascertain the rate of expansion of both large and small end bores over a range of temperature up to 180°C. from the results of which the attached curves have been drawn. At the small end, a gauge fit represents a diametral clearance of .000075 and a push or rotating fit a diametral clearance of .00025. This clearance would be insufficient. It is therefore suggested that in the initial assembly the clearance should be .0005, which under running temperature conditions in the region of 100 to 120°C. and taking into account the expansion of the gudgeon pin, should give a running clearance of .00075 to .001. At the large end, a gauge fit represents a diametral clearance of .00015 and a push or rotating fit a diametral clearance of .00035. An initial assembly clearance of .00075 is therefore recommended. Assuming a working temperature of 60 to 80°C. and making allowance for a crankpin expansion of .0005 to .001, running clearance under these conditions would be .0018 to .002. Standard Connecting Rods are assembled with small end clearances of .00075 to .00125 and large end clearances of .00175 to .002. We should like to know whether you are in agreement that the first set of connecting rods being prepared for test should be given the clearances stated. RHC.{R. H. Coverley - Production Engineer} [Signature] | ||