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 design and performance of distributor and ignition system components.
| Identifier | ExFiles\Box 164\5\ img110 | |
| Date | 3rd December 1931 guessed | |
| -2- The heel centre is approximately 1" from the pivot, so that .002" wear on the heel causes the contacts to close .003". The flat spring not definitely attached to the lever is used in conjunction with a separate flexible earthing connection, one end of which is screwed to the lever and the other end to the body. The end of the spring remote from the lever is bent round a rivoted arm which takes up any longitudinal movement of the spring. This would seem to be unnecessary and even undesirable, as it prevents the increase of spring pressure as the contacts open, which tends to reduce fling at high speeds. The fibre heel is held in place with two rivets, one parallel to the cam face and the other at right angles to it. The riveting is very poor, and, in the case of one of the rivets, has split the heel. The low tension terminal of the distributor consists of a screwed pin (with nut and spring washer) entering a moulded bush in the side of the casting and clamping the plate which carries the stationary contact. This plate is a bent piece of brass 3/32" thick which affords an inadequate length of thread for the actual contact screw, there being only two complete threads in the hole. It appears likely that a certain amount of wipe action would take place on the contact face, however, owing to the flexibility of the plate. The condenser is a large paper wound one enclosed in a narrow metal case which fits into a recess inside the body and is retained in place by a strong spring which presses the case against the side of the distributor body. The side of the condenser case had been distorted by the spring. The capacity of the condenser is 4 to 5 times that which we have to be the optimum value for 12 volt ignition coils. Endurance tests made here show that increasing the capacity of condensers beyond .12 mfd actually causes more wear of contacts, and the analysis sheet attached shows the large falling off in performance due to the large condenser. This condenser is also very leaky, as 39% of its was lost in 10 seconds. While it has never been proved that a leaky condenser is any worse as regards contact wear, it is extremely likely that a leaky condenser is more liable to break down. Ignition Coil. This is of the inside primary type and is enclosed in a bakelite moulding with a removable moulded cover over the low tension terminals. Contact is made to the H.T. cable by means of a pointed screw which pierces the insulation of the cable, the screw being moulded into a large serrated head. This H.T. terminal is situated on the side of the coil. The two tapped brass inserts are provided in the base of the coil for fixing purposes. | ||