As the shaft E rotates and carries with it roller I, the roller makes contact with the sectors in order B-C-D-A, if rotated in the direction shown by arrow, which rotation grounds the primary coils of the spark coils R3-R4-R1-R2 in succession; the connection from the timer to the primary being to the primary binding posts P3-P4-P1-P2. A high tension spark occurs at each contact of the roller with the sectors, as the contact allows current to flow through the primary of the coils. The high tension binding posts S1-S2-S3-S4 are connected with the spark plugs or spark gaps U1-U2-U3-U4 by means of high tension cables. As soon as the timer grounds a coil, the coil produces a high tension spark in its corresponding spark plug.
It is evident from the foregoing that the timer not only determines the time at which a spark will take place, but it also determines the cylinder in which the spark will be produced, providing of course that a spark coil is provided for each cylinder.
The contact sectors A-B-C-D are insulated from each other by the insulating walls W-W-W-W, the inner surface of which provides a path on which the contact roller I revolves.
The contact sectors and insulating walls are encased by the protective housing Z, to which they are rigidly fastened.
The housing Z can be moved back and forth on the shaft E for advance and retard, by means of the lever K.
The current flows from the battery terminal V (with the roller in the position shown) through the switch M, through coil R3, post P3 to sector B, from which it passes through the roller I, levers H and F to ground. From the ground on the engine frame the current flows back to its source, the battery O, thus completing the circuit. When the roller makes contact with sector C, the coil R4 is energized, contact with D energizes R1, and so on. No two coils can be thrown on simultaneously as only one coil is grounded at a time. The high tension current flows from each coil to its plug as soon as the current passes through the primary of that coil.
In some timers, the current is taken from the revolving arm through a separate connection to ground instead of grounding the shaft through the bearings. With these timers, the connection is not affected by worn bearings or an oil film that tends to insulate the shaft from the bearings.
(94) Operation of Timers.
Timers frequently cause misfiring which is generally due to dirt or oil getting between the contacts, or to the wear of the insulating walls W-W-W-W, or to the wear of the moving parts.
Dirt or gummy oil will prevent the contact coming together and completing the circuit, or will clog up the rollers or levers so that they cannot perform their functions properly. This will of course interfere with production of the spark.