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).
Technical analysis of ignition spark timing and retard settings, including a formula.
| Identifier | ExFiles\Box 54\5\ Scan310 | |
| Date | 17th December 1928 guessed | |
| -3- Contd. The circumstances may be such that it is less than 60°, in which case a spark could not be produced by retarding the lever. The fraction reckoned from the retard end of the range of the advance lever up to the point where the spark would be caused on retarding is f = S - 120r + d ---------- R If S were 66°, R 40° and r and d as above, then f = 66° - 66° + 10 ------------ 40° = 1/4 implying that the spark would occur after having retarded 3/4 of the full amount from the advanced position. It is further seen that the larger S is, or d is made, the more certainty there is of the break coming on the range of retard, and the larger r is, the less certainty there is of this occurring. Thus it is important from this point of view that the platinum gap should not be allowed to be so small that r shall exceed .55. r is made .55 in the first instance because it is likely that in the long run at any rate the platinum points will wear more relatively than the rubbing block, thus giving a tendency for r to be reduced. It is also clear that the ignition setting at full retard should not, from this point of view, be altered to be much less than 5° A.D.P. EFC. {E. Fowler Clarke - Electrical Engineer} | ||