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).
Investigation into crankcase cracks on two test bed engines and proposing solutions.
| Identifier | ExFiles\Box 182\M19\ img226 | |
| Date | 31th August 1931 | |
| To R.{Sir Henry Royce} From Ha/Gry.{Shadwell Grylls} c. to Sg.{Arthur F. Sidgreaves - MD} Mor. c. to E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design} c. to By.{R.W. Bailey - Chief Engineer} ORIGINAL Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls}2/WJ.31.8.31. P.11 CRANKCASES. X7000 Two of our test bed engines, each of which has done about 400 hours running, have developed cracks in the crankcases. In one engine the top half is extensively cracked in the vicinity of the centre journal. The webs of journals 3 and 5 are also cracked. We are sending you photographs of this crankcase. In the second engine both the top half and bottom half are affected. The flange of the top half is cracked as in the engine shewn in the photographs, and on both sides horizontal cracks are spreading from the inside of the crack in the flange. The bottom half on one side has a horizontal crack about one inch below the centre journal and about two inches long. We think the cause of these cracks is that the crankcase is insufficiently strong laterally to withstand the forces on the centre main journal. The cracks in both cases have spread from the outside of the flanges inwards. We have no evidence of cracked crankcases in cars the defect being only confined to test bed engines. The forces on the centre journal would of course be reduced by balance weights and the balanced shaft to L&S.2925 will be a great improvement in this respect. That shaft, however, necessitated a new forging. With the present forging we can increase the journal diameter by 1/8" to 3/16" and also the width of the web at right angles to the length of the shaft by about 1/8 to 1/4. Increasing this latter dimension has been found to increase the stiffness on aero shafts. Our object in fitting balance weights to the Phantom engine is not smoothness as on the 25 HP, but solely to increase bearing life. Making the suggested shaft from the existing forging we could probably balance about 2/3 of the crankshaft or just under half the centrifugal bearing loads of the centre and end journals using R's. eight weight scheme or rather less on these bearing and more on the others, using the Chrysler scheme. Photographs attached to R.{Sir Henry Royce} E.{Mr Elliott - Chief Engineer} By.{R.W. Bailey - Chief Engineer} Ha/H...ll-- | ||