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).
Request to produce two experimental sets of connecting rods and bearings for the Wraith III model.
| Identifier | ExFiles\Box 115\3\ scan0076 | |
| Date | 23th October 1937 | |
| To HPS.{Horace Percy Smith - Experimental Factory Mgr} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} c. whym. 1020 Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}1/AP.23.10.37. WRAITH III. Will you please produce two sets of connecting rods and bearings as follows:- (1) A.C. big end bearing shells .062 thickness of section. (2) The housing bore of the connecting rods will be reduced accordingly, it will be necessary therefore to take rods before the bore has been machined to the existing Std. dimension. The dimensions of the outside diameter of the bearing and the housing bore of the rod should be such that there is a diametrical interference fit of .00075 with limits to give size and size. (3) Dowels to be fitted in both rod half and cap half to locate the bearing shells similarly to way it was carried out by you on Ph.III. in accordance with x.28937/8. This has proved very satisfactory on Ph.III. endurance and automatically deletes the use of shims. (4) Bearings to stand proud of joint faces by .0005 on each half to give 'nip' of shells. (5) Bearing clearance diametrically on the crank-pins to be between the limit of .002-.00275. It is intended to run one set on endurance and if successful other set will be run on 15,000 miles test. The object of reducing the sectional thickness of the bearing shell is to prevent the pistons hitting the cylinder head in case of bearing failure. We would like your opinion regarding the advantage of producing bearing nip by deletion of shims. It is understood that production have difficulty of giving the correct nip on the Bentley where shims are used. The reduced bore of the rod will, to a slight extent, increase the reciprocating weight which we do not anticipate will be noticeable. This will be offset by having a stiffer rod with a reduced tendency to distortion as at present experienced on Bentley when in service. We are anxious to get started with this experiment as soon as possible, and would be glad if you will regard it as very urgent. | ||