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 issues with AC.2 bearings in Bentley engines, comparing them with AC.7 metal.
| Identifier | ExFiles\Box 114\3\ scan0047 | |
| Date | 5th December 1938 | |
| To By.... from Rm{William Robotham - Chief Engineer}/GWH.{George W. Hancock - Head Chateauroux} BENTLEY - Re: AC.2. BEARINGS. ------------------------- You will have received K/KC's reports on six chassis dealt with. The results of the findings, may possibly confuse the issue of finally stating whether or not the whole of the engines fitted with AC.2. should be changed. In view of the conditions in which the bearings have been found, I personally still maintain that only known hard drivers should have the bearings changed at once, the remaining to be dealt with as they come in for top or bottom decarbs. My reason for this is the result of the following investigations:- (1) The oil flow test result was confusing, the times recorded being in the region of 4 mins. (2) This time from all our previous tests should have shewn the position to warrant attention i.e. bearings slack in the housings, whereas the condition of the bearings proved that they would have run a considerable mileage under normal running conditions. (3) The explanation of the oil flow time being 4 mins. is due chiefly we found to bearing clearance of the centre bearing, and a general increase of bearing clearance in the remainder, but it has not been due to excessive slack developing of bearings in the housing. (This is the danger point of AC.2. metal, in so much that it does not give the warning as the AC.7. material does). (4) The difference between the AC.7. metal and AC.2. is AC.7. hammers out more readily and becomes slack in the housing if not pressed in with more preloading, than AC.2. (5) The reason then that an engine fitted with AC.7. metal with a flow time of 4 mins and requires attention is due to the escape of oil through the housing rather than actual bearing dia. and being slack in the housing causes a rough engine and thumps. Cont'd..... | ||