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).
Tappet and valve bounce issues on the Phantom engine, with conclusions and proposed solutions.
| Identifier | ExFiles\Box 17\6\ Scan195 | |
| Date | 20th February 1934 guessed | |
| -3- PHANTOM. This set of tappets gave similar troubles to the Vulture set, the eccentric bearing clearance having to be increased to .0025" before they would operate at all. The valve bounce speeds (the head was fitted with standard valves and springs) was 3100 r.p.m. approx., No. 1 inlet valve showing signs of this trouble before any of the other valves. We are at present waiting for a set of stiffer springs to try on this head. This set of tappets which was working reasonably well on its own cylinder head was then tried on the Vulture cyl. head (with the very strong valve springs) - it exhibited the same signs as the previous set, intermittent sticking of the eccentrics. CONCLUSIONS: (1) If these tappets are to be used on any cylinder head, the valve bounce speed of the valves must be put well above the max. engine speed obtainable, either by re-design of the springs, which will necessitate very heavy loadings on the timing gears, or by re-design both of the springs and camshaft. NOTE The effect of the valves being held off their seats owing to this valve bounce effect is not only that of dropping the top speed power - it results in grooving of the tappets running on the camshaft and will scrap the camshaft in a very short time, less than half an hour's running at top speeds on the test bed under these conditions was sufficient to ruin a complete set of tappets. (2) Owing to variations in height of pedestals, plunger casings etc. allowed by limits, and also owing to valve spring loading (especially in case of highrating and loading of springs), heat effects etc., considerable distortion of rocker shaft takes place, resulting in failure of eccentric bearings to function correctly. As soon as possible we shall obtain figures showing distortion of shaft due to clamping and valve spring loads, but it is difficult to measure the distortion under actual running conditions. Either a more effective type of bearing for the eccentrics must be found, or else a stiffer rocker shaft and better methods of clamping it down must be used. At present, if the eccentric bearings are examined, it can be seen that owing to bowing of the shaft, they are only bearing at their ends, resulting in a very small bearing area. In any case, such a bearing, which depends | ||