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).
Tests to determine the variation of tappet clearance during the warm-up period of the 1st Japan 3 Unit.
| Identifier | ExFiles\Box 179\3\ img016 | |
| Date | 2nd March 1932 | |
| ORIGINAL T. From Hs{Lord Ernest Hives - Chair}/Wths. C. to Sd. Mr. C. to S. My. C. to Dm.{D. Munro} Hs{Lord Ernest Hives - Chair}/Wths.2/MA.2. 3. 32. 1st JAPAN 3 UNIT. X5770. Since our report of the 19.2.32., we have carried out the following tests on the above unit. Tappets. Tests have been made to determine the variation of tappet clearance during the warming up period. The tappets were first of all set at .006 with the engine cold and were again checked after the engine had been warmed up rather quickly to 50°C water temperature, the oil at this stage of only a few minutes running was of course comparatively cool so that the push rods had hardly expanded at all whereas the crankcase top half and cylinder block and head had expanded quite an appreciable amount. The tappet clearance was then found to have increased to .012 to .014 on all tappets except those with overhanging rockers, in this case the clearance was found to be .018 and tappets very noisy. The engine water was then cooled off and the clearances again checked, in this case of course the cylinder block and head contracted to approximately their original dimensions but the push-rods were slightly warm due to the heat transmitted to them by warm oil after contact with cylinder head, and by heat radiated by warm cylinder block and head, the tappets were then found to have no clearance at all and in one or two cases the rockers were exerting considerable pressure on the valves and very nearly opening them. The tappets resumed their normal clearance when the engine had thoroughly cooled down. The test on the tappet mechanism confirms our suspicion of a bad warming up period and with this construction of aluminium top half, cylinder block and cylinder head (the rocker pedestals of Duralumin also making conditions worse) it seems evident that some form of self adjusting tappets are necessary in order to maintain silent tappet operation. | ||