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).
Analysis of engine big-end bearing failures, investigating causes related to oil flow and testing alternative bearing schemes.
| Identifier | ExFiles\Box 141\2\ scan0226 | |
| Date | 22th July 1940 | |
| - 4 - Cont'd.{John DeLooze - Company Secretary} Lr{Mr Ellor}/GWH{George W. Hancock - Head Chateauroux} who compiled these records states that failure can occur on any big-end bearing and is generally due to the high inertia force of the oil preventing flow to the bearing surface at speeds greater than 3,400 r.p.m. The belief is firmly held by other people, however, that failures occur mainly on big ends 3 and 4. i.e. on big ends fed by part annular grooves in the main bearings. Furthermore, failures occur in the air and not on test, all pointing to an intermittent feed and aeration of the oil. Lr{Mr Ellor}/LBH{Mr Hall - Aero Design Engineer} states that this condition can be reproduced on test beds with the same consequent bearing failure. In the case of either or both of these troubles, the increased capacity increased pressure main oil pump introduced on Merlin XX by By.{R.W. Bailey - Chief Engineer} should do much to overcome them. 2. It had been suggested that intricate passages in the main oil system might be responsible for loss of pressure at the bearings. Since oil pressure is measured at the point where the main high pressure oil leaves the relief valve and therefore ceases to have a velocity head, it is not possible for any drop in pressure to take place unless a very great restriction is encountered. Since this does not occur it is safe to assume that oil reaches the bearings at the specified pressure. 3. A copy of a report by Lr{Mr Ellor}/AT on the rig testing of various proposed main bearing schemes is attached. The thin shell bearing referred to in Section A.3.b. is a two-piece bearing having a flange in L.T.I. (1% tin) and a thin shell in L.A.4. (4% silver.) Owing to it's flexibility a thin shell bearing does not tend to nip in. In this respect Vandervell bearings might be good, but H1/EJW considers that trouble might be experienced due to end rubbing caused by torsional vibration of the crankshaft. 4. With 1% tin lead bronze the centre main bearing becomes liable to failure as the result of T.V. dives in which the engine is running at 3,600 r.p.m. for a negligible power output. A polar loading diagram for the bearing running under these conditions has been obtained. - Continued - | ||