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).
Discussions on engine development, including bearing issues, crankshaft hardness, test conditions, and valve materials.
| Identifier | ExFiles\Box 173\1\ img332 | |
| Date | 26th January 1934 guessed | |
| -2- During conversation with Mr. Brown, one of their Engineers, development experience on Curtis main bearings was revealed, and whilst Curtis state all their lead bronze experience has been obtained with balanced crank-shafts, considerable development was carried out by Bohn's (who incidentally have full test bed equipment) at request of Army Flying Corps with Conqueror engine fitted with soft unbalanced cranks and I was shown copies of development reports; they have been through exactly similar troubles on center bearings, which were ultimately overcome by introducing external grooves and oil holes already stated. EQUIVALENT OF Whilst bearings completed type approval tests satisfactorily, it was found that center crank case bearing panel was fractured, consequently balance weight crank, with reinforced center crank case panels, was adopted. It was also stated that cranks should not be below 300 Brinell, as even with improved lubrication, scoring of bearing surface is liable to occur unless that hardness is obtained. Bohns stipulate that oil pressure should on no account be below 100 lbs.□inch. It should be noted that whilst eventually bearings proved to be satisfactory, the overspeed test, in this case only consisted of 30% overspeed or 3400 R.P.M. max. for period of 30 sec. restored to normal conditions for 2 min. and repeated 20 times making total 10 min. American high speed test conditions consist of running engine at normal power and speed, easing break to give 30% over speed and restore to normal, which therefore are light as compared with searching tests on R.R. engines running under light load at high speeds which imposes high inertia loads on bearings. All concerned consider high speed tests rediculous and point out diving cannot be continued for that period, therefore 20-30 second tests sufficient to prove reliability of engines under these conditions. ⊕ see next Page In the afternoon I visited Wilcox Rich and met Mr. Jardine and Mr. Heron who thought perhaps lead content was being misconstrued and pointed out that 6 C C lead per Imp. Gal. equals 4.8 C C lead Amer. Gal. and 4 C C of lead Imp. Gal. equals 3.3 C C Amer. Gal., and whilst Curtis' are in much the same position with regard to test bench results on valves, Conqueror engines are running satisfactorily with 6 C C lead in service, a resume of points discussed being: 1. No alternative valve seat materials have yet been tried, neither have stiffer seats been tested. 2. Sodium cooled valves were considered less liable to lead attach. 3. With stiffer cylinder heads which will eliminate distortion, fully cooled valves will be required. 4. It was not considered good practice to make flexible valves at least from results Heron had obtained. | ||