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 a 20/25 single-cylinder unit detailing performance, lubrication issues, and adjustable valve controls.
| Identifier | ExFiles\Box 133\2\ scan0008 | |
| Date | 21th March 1934 | |
| x4706 To Sg.{Arthur F. Sidgreaves - MD} From Hs{Lord Ernest Hives - Chair}/CHP. c. to Wcr. c. to E.{Mr Elliott - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/CHP.2/KW.21.3.34. 20/25 SINGLE-CYLINDER UNIT. This engine has now completed 16½ hours running on the test-bed. A large percentage of this time has been occupied in running-in, owing to the fact that three new pistons have already been fitted. We have experienced two partial piston seizures (Aerolite Pistons) at speeds above 3750 R.P.M. apparently due to inadequate lubrication. It will be remembered that this engine is fitted with a roller bearing crankshaft which is not fed with oil under pressure; therefore there is considerably less oil thrown up into the cylinder than is the case with a normal engine. The lubrication appears to be quite sufficient for speeds up to 3750 R.P.M. as this speed has been held for fairly long periods without trouble; but two minutes full load running at 4250 R.P.M. in the first case, and 4000 R.P.M. in the second, was enough to cause a seizure. We hope to overcome this trouble by fitting an oil jet in the side of the crankcase in such a position as to squirt oil onto the big-end of the connecting rod, and thus cause a greater amount of splash in the vicinity of the cylinder walls. Power and consumption figures up to 3750 R.P.M. will be found on Fig. 1. It will be seen from the B.M.P. curve that the power is still rising at 3750 R.P.M., and would apparently peak at between 4000 and 4250 R.P.M. The torque curve peaks at 2750 R.P.M. These figures were obtained with the normal Bentley valve timing of: I.O. 4º early, I.C. 51º late; E.O. 51º early, E.C. 7º late. The carburetter is a Zenith triple diffuser type, fitted with a 32 m/m.{Mr Moon / Mr Moore} choke. The induction depression at 3750 R.P.M. was approx. .525 ins. head of mercury. The effect on the power of varying the valve timing has not yet been tried out. Controls are fitted on the engine to vary - (a) The height of maximum valve lift from .345" to .419" in the case of the inlet; and from .337" to .413" in the case of the exhaust, to 252º (b) The duration of lift from 202½º (flywheel) for the inlet valve; and from 199º to 258º for the exhaust. (These figures refer to .020" tappet clearance) (c) The phasing of the timing over a total range of 20º (flywheel), for both inlet and exhaust valves. The inlet or exhaust valves may be altered in any of the above respects quite independently of each other. | ||