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).
The effect of increasing the primary gap on the high-speed performance of Watford and B.T.H. aero magnetos.
| Identifier | ExFiles\Box 43\4\ Scan057 | |
| Date | 27th January 1927 | |
| WC.3. 27.1.27. EFFECT ON HIGH SPEED PERFORMANCE (ADVANCED) OF INCREASING THE PRIMARY GAP ON WATFORD AND B.T.H. AERO MAGNETOS. Tests have been made to determine the above on Watford IS.12 magneto No.83119 and B.T.H.SC.12-7 magneto No.73791. In the case of the Watford the primary gap could be increased to .019" before any misfiring on 5.0 mm. gaps occurred; with this gap a speed of 4200 r.p.m. could be attained with the contact breaker fully advanced without any irregularity of H.T. sparking. When the gap was still further increased misfiring commenced at relatively low speeds. The normal primary gap for this magneto was .010". In the case of the B.T.H. with the primary gap normal, i.e. .011" the maximum regular sparking speed was 4400 r.p.m. With the primary gap increased to .016" this maximum advanced speed became 4100 r.p.m. The gap was then increased to .020" when missing commenced; as the speed was still further increased sparking was practically cut out. These tests shew that the Watford magneto gives the better high speed performance in the advanced position when the primary gap is increased. Watford - primary gap normal .010" - increased .009" to .019" - maximum speed for regular H.T. sparking on 5.0 mm. gaps in the advanced position 4200 r.p.m. B.T.H. - primary gap normal .011" - increased .009" to .020" maximum speed for regular sparking on 5.0 mm. gaps in the advanced position 2900 r.p.m. EFC/H.E.West. | ||