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).
Experimental lightening of a Bensport crankshaft and related design considerations.
| Identifier | ExFiles\Box 85\5\ scan0032 | |
| Date | 12th May 1933 | |
| X217 To Hs.{Lord Ernest Hives - Chair} from E.{Mr Elliott - Chief Engineer} c. Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} By.{R.W. Bailey - Chief Engineer} RHC.{R. H. Coverley - Production Engineer} Bensport Crankshaft. We have issued a lightened crankshaft for experiment to Hs{Lord Ernest Hives - Chair}/Gry{Shadwell Grylls}'s suggestion, with the bores of the pins and journals increased, and the balance weights widened and reduced in inertia. We think this is a good move, but we have not carried it as far as suggested for a number of reasons. Firstly, the crankshafts at present fail at the pins, hence we do not wish this part to be unduly weakened. there is no doubt that any 6 cylinder crankshaft will fail on the critical period, but we do often get just in the fringe without failing, and under these circumstances any concentration of stress at a weak point is liable to accelerate failure. Secondly, we think trouble in production is occasioned if the section of the pins and journals is unduly weakened in bending, for example, the rigidity of the crankpin if lightened out to the maximum amount suggested would be less than half the present pin. Thirdly, we prefer to test the shaft with a moderate amount of lightening carried out on it first, and having satisfied ourselves that it will stand we can then proceed to bore it out afterwards a further stage or two, and carry out further tests as regards its rigidity both for manufacture and performance. The shaft as instructed to LeC.3486 has the present degree of balance employed on the 20/25 production engine, and there is a saving in overall weight of 6½ lbs compared with 10 lbs obtained by the maximum boring out contemplated. Hs{Lord Ernest Hives - Chair}/Gry{Shadwell Grylls} has made some calculations for the various sizes of bores considered for the journals and pins, and it is found that the master period for the proposal instructed will only be reduced about 2 or 3% on the engine speed. Regarding the question of the failure of crankshaft oil caps, we are awaiting further information from you on this point. We find that the oil caps we have used have been made in RR.alloy and that this metal is reasonably tough at the high temperatures at which the failure you reported occurred. E.{Mr Elliott - Chief Engineer} | ||