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 report detailing measurements and fixes for engine connecting rod clearance issues.
| Identifier | ExFiles\Box 146\1\ scan0243 | |
| Date | 29th April 1938 | |
| Sr/VAI/ET.29.4.38 - 2 - We removed rather large "plugs" of decomposed oil and foreign matter from the oil ways in the crankpins, but we do not think that this was the cause of the trouble We measured up the crankpins and these were found to be 2.2485". We were informed by the Works, as per HPS.{Horace Percy Smith - Experimental Factory Mgr}I/VS.{J. Vickers} 30.IO.37 and Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}I/MH.{M. Huckerby}8.I2.37 that the diametrical clearance of the bushes on the crankpins should be between .00225" and .003". We made two mandrils which were ground true to the following size: 2.251 " 2.2505 " The remaining 5 rods were tried on the above mandrils. We noted the following: All rods found to be very light on 2.2505 diameter mandril and they could only just be moved on the 2.251" diameter mandril. We had in stock 6 new connecting rods incorporating big end bearing shells in Hall's A.6 alloy. These were also found to be tight on the above mentioned mandrils. We hand scraped all the big end bearings until they were a good bed and a free fit (with oil) on 2.251" diameter mandril. They were fitted up, engine erected and car then progressively tested and the engine found to be O.K. Since carrying out the above work, the car has covered I92I Kms. at slow, moderate and fairly high speeds, including a trip to Belgium and back. We think that the trouble was due to insufficient clearance. With reference to the dismantled rods, we propose to make them a free fit on the 2.251" diameter mandril (with the exception of N°6 rod, which we will return to the Works for reconditioning) and then take them into our stock at IOO% value, especially as duty has been paid on them. Sr/VA. | ||