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).
Experiments carried out on bearings for the 4 1/4 litre Bentley.
| Identifier | ExFiles\Box 115\1\ scan0126 | |
| Date | 15th November 1936 | |
| 1020 To ~~Mr. H~~ from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} File C. to E.{Mr Elliott - Chief Engineer} C. to ~~Mr~~ Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}10/AP.15.11.36. BEARINGS. We have recently carried out a number of experiments on bearings, with a view to overcoming the following principle troubles which have occurred with Hall's Solid Metal now standard on the 4 1/4 litre Bentley. 1. Complete failure of big end bearing during 15,000 miles French test in which the bearing was crumbled to pieces. 2. Hammering out of the rear main bearings creating excessive clearance and engine roughness. No.1. being the most serious this was tackled first and actually the big end failures were a surprise to us in view of several 50 hr. and 100 hr. endurances which had been carried out on the test bed without failure. It was decided to run 1/4 load endurances in order to represent the throttle being closed after running full throttle at high engine speeds on the road. This gave us the results we had been looking for and the average running time before a big end seizure with any type of Hall's metal was 2 hrs. under these conditions. Each hour of endurance at 1/4 load was composed of:- 30 mins. at 4000 R.P.M. 25 mins. at 4250 " 5 mins. at 4500 " the inlet oil temperatures being at 100°C. and oil pressure of 30 lbs.sq.in. The type of Hall's metal run was (AC.7.std), AC.4, AC.2 and (AC.1.Forged) the numbers representing the percentage of tin in the alloy. In the main Nos.2 and 5 big ends comprised the majority of failures and it was noted that the cap half was the half where the seizure commenced. This indicated that the reduced pressure on the rod half of the bearing by the 1/4 load running is, on the upward stroke overcome by the inertia of the rod, resulting in loading on the the cap half, thus destroying the oil film. continued. | ||