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).
Main bearings, discussing issues with forged aluminium liners and recommending a new design without liners.
| Identifier | ExFiles\Box 115\3\ scan0096 | |
| Date | 15th November 1937 | |
| To HY.{Tom Haldenby - Plant Engineer} & Rm.{William Robotham - Chief Engineer} c. to Hs.{Lord Ernest Hives - Chair} Da.{Bernard Day - Chassis Design} c. to Ha. Hr. 1020 SWDL{Len H. Swindell} RHC{R. H. Coverley - Production Engineer}/SB.{Mr Bull/Mr Bannister}6/MJ.15.11.37. MAIN BEARINGS. The present Bearing Assembly on the Bentley [strikethrough] engines incorporates a forged Aluminium Liner for the purpose of adjusting bearing sizes during overhauls and preventing rotation of bearings. The fact of this Liner being produced in forged Aluminium introduces certain difficulties in manufacture which prevents sizing by any reliable machine process whereas the Steel Liner formerly used could be produced to the required thickness by surface grinding. Whilst boring the crankcase it is necessary to use temporary steel packings which are later replaced by the forged aluminium Liners referred to and the slightest difference either in thickness or parallelism between the temporary and finished Liners results in a distorted crankcase bore. In order to guarantee that equal "nip" is provided it is essential to machine individual half bearings to a predetermined height above the cap or housing face, because it cannot be guaranteed that the liners are exactly on the centre line of the crankshaft bore. The introduction of Aluminium Alloy also demands a change in assembly conditions owing to the unstable nature of the material, which requires an increased "nip" as compared with the previous steel backed bearings. It is therefore recommended that the present method of construction be abandoned owing to the difficulties outlined above, and that bearings in true halves be introduced having butted faces and no liners. The fact of deleting liners would permit of bearings being finally sized internally and externally before assembly to predetermined dimensions which would be arranged to give the correct amount of 'nip' in the crankcase and a suitable contraction allowance in the bore. This will eliminate the practice of final reaming after assembly which is liable to affect alignment of the crankshaft with the camshaft because there is no guarantee that the bearing bore will be concentric with the housing, the result being that inaccuracies crepp in with regard to the gearing and introduce difficulties in connection with gear quietening. | ||