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 the tightening of big end bearings and the resulting effect on oil consumption and pressure.
| Identifier | ExFiles\Box 114\3\ scan0131 | |
| Date | 30th September 1937 guessed | |
| -3- bearings when they are effecting change overs. The Depots on one hand maintain that they are giving the recognised bearing clearance, whereas I on the other hand have found the big ends are tightening up. The case I have in mind is Embricos' 4 1/4 litre. The big ends fitted by K in a normal manner were found by me when the engine was dismantled at the Paris Depot to have tightened up considerably. Another case was B.202.GA 4 1/4-litre. This car came into K with a poor oil consumption soon after Derby had attended to main and big end bearings. (A complaint of main bearing thump - recurrent). K called my attention to the fact that these rods were tight. Mx{John H Maddocks - Chief Proving Officer} will remember the case, as when he called at K his attention was drawn to them by me. These are not isolated cases and this tightening up has been worrying us for some time, although we are of the opinion that bearings that have been in use for a considerable mileage let together and nipped up are not so prone to this tightening up phenomenon, and in these cases we are of the opinion that the standard clearances are sufficient, but with new big end bearings we are of the opinion that the standard clearance is not sufficient, and that this clearance must be increased to approx. .003 to avoid the tightening up. This was proved to our satisfaction in the case of B.117.JY with the two new bearings fitted. No 4 & 5 were given the extra clearance on journal dia and which on dismantling on this occasion were perfectly normal in every respect and were a 100% job. From the condition of the big end shells that I have examined I have come to the conclusion that the distortion, bell mouthing and rolling up of the metal shells is the indirect result of the tightening up of these bearings on the pins. The direct cause of the trouble being excessive local oil temperature rise due to inefficient ventilation. Another aspect of this tight bearing question is the rise in oil pressure and the effect it has on poor oil consumption. In the first case the high oil pressure lulls an owner into a feeling of false security and in the second case an engine fitted with drilled con.rods, the oil feed to the cylinder walls is greater than can be coped with by the standard scraper rings, also the oil flow to the cylinder walls does not cease at the low r.p.m. as would be the case in a bearing with normal leakage and clearance. 3. Bearing nip or precluding the bearing shells in their housing. As I am of the opinion that journal and pin clearance -contd- | ||