meet squarely across the entire face. The rotor distributes the high tension current from the center of the distributor to the proper cylinder. Care must be taken to see that the distributor head is properly located, otherwise the rotor brush will not be in contact with the terminal at the time the spark occurs.

Combination Switch. The combination switch is located on the cowl board and makes the necessary connections for ignition and

lights. The "M" button controls the magneto type ignition and the "B" button, the dry battery ignition. In addition to this both the M" and "B" buttons control the circuit between the generator and storage battery. When the circuit between the generator and the storage battery is closed by either the "M" or "B" button on the combination switch, the direction of flow of the current is from the battery to the generator when the engine is not running,

as well as when it is running below 300 R. P. M. But the amount of current that flows from the battery at the lowest possible engine speeds is so small that it is negligible. That used on Buick 1915

cars is shown at Fig. 44, the type supplied on 1916 cars is outlined at Fig. 42.

To Time the Ignition.-1. Fully retard 2. the spark lever. Turn the engine to mark on flywheel about one inch past dead center to the ""7 degree" line, with No. 1 cylinder on the firing stroke. 3. Loosen screw in center of timing mechanism (Fig. 45) and locate the lobe of the cam

proper

by turning until the

Fig. 46.-How Cover is Removed from Delco Distributor.

button on the rotor comes under the high tension terminal for No. 1 cylinder. 4. Set this lobe of the cam so that when the back lash in the distributor gears is rocked forward the timing contacts will be open, and when the back lash is rocked backward the contacts WILL JUST CLOSE. Tighten screw and replace rotor and distributor head. The construction of the distributor head is clearly shown at Fig. 42, which shows the internal view, while Fig. 46 shows the exterior and plan of contact brushes.

Fig. 47.-Parts of Westinghouse Timer-Distributor, which Includes the Induction Coil.

Westinghouse Vertical Ignition Unit.-The Westinghouse vertical ignition unit, shown at Fig. 47, can be used for ignition from storage batteries or plain lighting generators. This set contains interrupter, spark coil and condenser, and distributor, all in one unit. One wire from the battery or generator to the ignition unit and one wire to each spark plug are all that are requiredthe simplest possible connections. The interrupter, located at the lower end of the set, has the same type of circuit-breaker as that

on the Westinghouse ignition and lighting generators, but no automatic spark advance feature. It can be used equally efficiently for either direction of rotation without change. The interrupter is enclosed by a spring collar which can be readily removed for inspection or adjustment of the contacts. The collar makes a tight joint and is clamped by a screw which prevents it from slipping.

The spark

coil is embedded in heat proof insulating material, and the condenser is well insulated. Both are contained in a tube of Bakelized Micarta which forms the body of the unit. The distributor is of very simple construction. with a wiping brush contact of the same type as that used on the ignition generators. It clamps to the upper end of the set. The wiring diagram of this system is shown at Fig. 48. The device

To Spark Plugs

Distributer Brushes

Induction Coil

Interrupter
Contacts

is sometimes mounted in connection with a generator when that member is driven by direct gear connection from cam shaft which provides a properly timed drive for the ignition unit. This method of application is clearly shown at Fig. 49.

Spark Plug Design and Application.-With the high-tension system of ignition the spark is produced by a current of high voltage jumping between two points which break the complete circuit, which would exist otherwise in the secondary coil and its external connections. The spark plug is a simple device which consists of two terminal electrodes carried in a suitable shell member, which is screwed into the cylinder. Typical spark plugs are shown in section at Figs. 50 and 51, and the construction can be

easily understood. The secondary wire from the coil is attached to a terminal at the top of a central electrode member, which is supported in a bushing of some form of insulating material. The type shown at A employs a molded porcelain as an insulator, while that depicted at D uses a bushing of mica. The insulating bushing and electrode are housed in a steel body, which is provided with a

screw thread at the bottom, by which it is screwed into the combustion chamber.

When porcelain is used as an insulating material it is kept from direct contact with the metal portion by some form of yielding packing, usually asbestos. This is necessary because the steel and porcelain have different coefficients of expansion and some flexibility must be provided at the joints to permit the materials to expand differently when heated. The steel body of the plug which is screwed into the cylinder is in metallic contact with it and carries sparking points which form one of the terminals of the air gap over which the spark occurs. The current entering