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).
Experiences with fitting aluminium and Zephyr pistons, including issues with clearances, piston knock, and performance over mileage.
| Identifier | ExFiles\Box 35\2\ scan 030 | |
| Date | 14th November 1918 | |
| X3400 R.{Sir Henry Royce} from EP.{G. Eric Platford - Chief Quality Engineer} Extract from Ep{G. Eric Platford - Chief Quality Engineer}3/F141118 c. to CJ. c. to EH. c. to EY. X.3400/2. With reference to your memo R1/C3D1018, referring to aluminium pistons for cars, a copy of which I attach, I am very anxious that our valuable experiences with reference to aluminium pistons in cars should not be understood. It is certainly a fact that when we first turned out Commander Briggs' car, 64-LB, with the barrel type aluminium pistons, there were no audible piston knocks. In tackling the job, however, a considerable amount of time was spent in continually easing the pistons after running, this being done six or seven times, in order that the engine could be safely runs under full power, high speed conditions on the dynamometer, without seizing up. This we did in order that we could have the closest fitting pistons, and avoid piston knocks. The minimum clearance was about .008 to .009". We found we were not able to produce this clearance by one operation, owing to the considerable distortion which took place, which was not regular or consistent, and we started with pistons which were .006" clearance, and then commenced our running and easing. Commander Briggs, after running the car, also confirms the above, but it was not very long before he pointed out that piston knocks were slightly audible, but as far as he was concerned, it was of no consequence, as the engine itself in other respects was running excellently. When the car was returned to the Works, however, after about 20,000 miles running, piston knocks were distinctly bad, and in taking measurements of clearances, we could only discern about an extra .001" clearance, the piston having worn. Zephyr pistons were fitted later, as per your instructions, but we were not able to obtain with these such success as regards absence of piston knocks. At the same time, we also fitted the high lift camshaft, and there was an all round increase in power. The car has since run 30 to 40,000 miles, and two of these pistons have smashed. EH. has kept in touch with these tests, and I understand has reported to you in detail. | ||