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).
Report page detailing various valve timing comparisons in a table and discussing resulting mechanical troubles, specifically valve bounce.
| Identifier | ExFiles\Box 133\2\ scan0082 | |
| Date | 11th October 1934 guessed | |
| (6) VALVE TIMING. In order to make comparison easy, the various valve timings to which reference is made in this report are tabulated below:- I.O. I.C. E.O. E.C. Overlap 1. Standard Bentley ........... 4°E 51°L 51°E 7°L 11° 2. For best power at 3000 RPM. 14°E 36°L 52°E 8°L 22° 3. " " " but overlap } 10°E 36°L 52°E 2°L 12° limited to 12° } 4. " " " but at 2000 } 6°E 16°L 49°E 6°L 12° RPM. } 5. For best power at 4000 RPM. 11°E 44°L 56°E 11°L 22° No. 2 Ramp head gives the best power curve when using the second of the above timings, but, owing to the undesirable amount of overlap, the third is suggested as a more suitable one; this causes no sacrifice in power up to almost 1750 RPM., but a gradually increasing loss from that speed up to 2% at 2500 RPM. which loss is then maintained throughout the rest of the higher speed range. This is illustrated on Sheet 4 of the curves. When using the standard Bentley timing, the No.2 Ramp is actually worse than the standard below 2500 RPM.; a curve taken with standard timing is shown on Sheet 3 (full-line curve). The fourth timing improves the power output up to 2500 RPM, but at the cost of a large power loss at higher speeds (Sheet 6). The fifth timing gives slightly more power than the second at speeds above 3750 RPM, but is inferior below that speed. MECHANICAL TROUBLES. VALVE BOUNCE. Since fitting the strengthened tappets and push rods to Lec.4048 we have been troubled with valve bounce at 4500 RPM, presumably due to the extra mass of the new tappets etc. Double valve springs have been tried, but these do not improve matters. If the duration of the valve lift is reduced but slightly, trouble is experienced at approximately 4200 RPM. It seems indicated that considerably stronger springs should be fitted to the inlet valve in order to overcome this trouble. | ||