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).
Test report on grooved main bearings for Kestrel and Goshawk aero engines to increase oil flow.
| Identifier | ExFiles\Box 179b\3\ img184 | |
| Date | 10th February 1933 | |
| ORIGINAL To R.{Sir Henry Royce} From Ha/Pmr. c. to Sg.{Arthur F. Sidgreaves - MD} c. to Wor.{Arthur Wormald - General Works Manager} c. to Rg.{Mr Rowledge} c. to E.{Mr Elliott - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} Ha/Pmr.3/MJ.10.2.33. x2965. x 3859. AERO ENGINES. Grooved Main Bearings. In consequence of a number of connecting rod big end bearing failures on both the Kestrel and Goshawk type engines, a scheme in which the main bearings are grooved to allow the uninterrupted oil flow to the big end journals, and consequently increase the oil flow to the bearings, has been tested on a Goshawk type engine having articulated rods and Lead-Bronze bearings. Kestrel 27 engine was used for the tests, the main bearings being modified to drawing E.36327, in which the grooves are arranged so that the feed passages to the journals are in constant communication with the main feed to the bearing instead of intermittent as on the existing type. The result of the modification is such that the oil flow to the big ends is considerably increased and serves a dual purpose of maintaining an increased supply of oil to the bearing for lubrication, and consequently better cooling of the bearing. The conditions under which the tests were carried out consisted of the endurance running of the special Category Type Test, i.e. 591 BHP. at 2750 R.P.M. using special fuel, and F.2 oil. At the commencement of the tests it was found that the oil pressure was lower than previously, and decreased considerably as the temperature increased. It had fallen to 30 lbs/sq.in. before the normal working temperature of 70°C. inlet had been reached. This we considered due to increased oil flow past the bearings and consequently decreased pressure. The relief valve to the system was fitted with a much stronger spring in order to maintain the pressure as close to normal as possible, but the pressure again decreased with temperature, which shewed that the valve was permanently closed and the pressure was only 41 lbs/sq.in. at 70°C. temperature, so the tests were carried out with a main oil temperature of 65° instead of the usual 70° in order to maintain the pressure as close to 50 lbs/sq.in. as possible; actual average pressure being 47 lbs/sq.in. We then ran the engine for a period of two hours at 2750 R.P.M. developing 591 BHP., and then stopped in order to examine the oil filters. These shewed perfectly clear, no indication of bearing trouble, and therefore a further two hours running was carried out under the same conditions and the subsequent examination of the filter shewed no indication of bearing failure. | ||