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 excessive oil consumption and bearing issues on Chassis 93 NK.
| Identifier | ExFiles\Box 71\4\ scan0277 | |
| Date | 6th July 1925 | |
| X8940 Hotel de France, Chateauroux, Indre. France. To: "HS{Lord Ernest Hives - Chair}" From: G.W.Hancock. GWH.{George W. Hancock - Head Chateauroux}I/Crn.6.7.25. Re Chassis 93 NK. We held the car up in the garage yesterday to try and investigate the cause of our excessive oil consumption. We dismantled the bottom half, and by contriving we managed to rig it up so that we could obtain an oil pressure on the crankshaft, with the engine standing. We observed that oil poured from the crankshaft bearings. Nos. 1, 2, 3, 4, 5 & 6 - oil literally poured from these. No. 7 was not bad. This is accounting for our drop in oil pressure, when the oil gets hot. We also assume that this has a lot to do with the oil consumption becoming poor; as a quantity of oil is thrown up into the cylinders, with the oil streaming on to the webs of the crank, the quantity being so great that the piston rings cannot deal with it. The piston rings in question did not shew an even bed all round when we dismantled the pistons to fit the new rods. From looking at the piston rings, we could not definitely state whether they have worn oval, as you stated was the case when piston rings were lapped. We dismantled all the main bearings of crankshaft to see whether there was anything silly in the refitting of these the last time the bearings were down, but everything is O.K. With the bearings in this condition, we think it is useless trying to get any sort of oil consumptions. To try and rectify these here would be a mistake. To do this the engine wants taking out completely, and the crank bedding down to the bearings in case, then the packing pieces would have to be reduced and the top caps then rebedded. We consider this is too big a job for us here, also we think that it is a much better policy for these bearings and the crankshaft journals to be measured up when the car returns to Derby, so as to obtain the actual wear on same. This does not mean that the car is unrunable, as at speeds over 25 to 30 m.p.h., the oil pressure is O.K., except when the weather becomes hot, when our oil pressure drops to 17 lbs. We dismantled the whole of the conrod bearings, and found that No. 1 conrod bearing has already got a small crack. Nos. 2 & 6 have also started to crack. No. 2 conrod was evidently the one that caused the engine to tighten up, as this rod shewed signs of a slight seizure, but nothing detrimental. This has been rectified in the refitting. We are sending you a diagram of the conrod bearings, shewing the positions of cracks, etc. We are continuing our running tests to-day, and shall | ||