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).
Power development through modifications to cylinder head Ex.22594, detailing changes and test results.
| Identifier | ExFiles\Box 82\4\ scan0381 | |
| Date | 1st October 1936 | |
| -4- PART 2. Power Development. The cylinder head was now modified in the following way, from the results in Part I of this report. Modified Cylinder Head Ex.22594 :- (a) General thickness of combustion chamber walls reduced. (b) Water passages cleaned up round the combustion chamber, by deleting webs supporting stud bosses. (c) Lower sparking plug position, thus increasing the water space above it. The two water holes in the head face immediately below the plug joined into one long slot, to allow water to pass freely below the plug. Eight of the corresponding holes at front end of the cylinder block blanked up to even up the temperature in the head. (d) Exhaust valve guide boss lowered, causing less area of valve stem to be exposed to flame, and the water space being brought down behind the guide boss, thus increasing the water space round the valve. Results. A very big improvement all round in the cooling of the head. The compression ratio was raised to 9 : 1, with further slight advantage, but no apparent disadvantage. Nothing was gained by raising the ratio above 9 : 1 however. As a further endeavour to cure valve pocketing, another identical head was made and tested, the only difference being that the valve seats had been chilled during casting. It certainly had the effect of hardening the seats, as experienced in the efforts to machine the valve seats. This test, as far as it was taken, looked promising, and showed a slight improvement in pocketing. The endurance test was however cut short by a piston failure; the piston breaking in two parts above the gudgeon pin boss. The break originated in the "heat-Break" saw cut in the ring groove. The piston failure was not considered to be serious, as it had completed a total running time of over 80 hours, including power curves, of which 47 hours was high speed, full throttle work. | ||