FIG. 53-B. How A STORAGE BATTERY IS MADE

must be charged with a current generated by a dynamo.

Now a dynamo and a motor are made exactly alike,

FIG. 53-C. THE ELECTRIC ENGINE DRIVE

and if you rotate the armature the machine will generate a current, and then it is called a dynamo; on the other hand if you pass a current through the

machine it will rotate the armature and then it will be a motor.

The motor drive is the mechanical part of the starter; it is formed of a screw gear mounted on the projecting shaft of the electric motor; it meshes with teeth that are cut on the rim of the flywheel of the engine, as shown at C, and demeshes from it after the engine is started. It is shown complete at D.

FIG. 53-D. THE ELECTRIC STARTER COMPLETE

The switch is a simple device for opening and closing the circuit. Now when you throw on the switch the storage battery energizes the motor and this screws the drive gear into the flywheel and turns it; as soon as the engine has started, the motor drive demeshes automatically; you release the switch and the electric motor stops. When the engine is running the motor can then be driven by it, and it will then generate current and charge the storage battery.

The Knight Sleeve Engine.-To get rid of the noise that the poppet valves make, Knight invented

an engine in which the inlet and exhaust ports are opened and closed by a sleeve that slides between the cylinder and the piston. It is shown in Fig. 54.

PART III

THE MOTOR BOAT GASOLINE ENGINE

Gasoline engines for motor boats are of the two and four cycle types and are made with one, two, four, six and eight cylinders.

The Fuel Feed System Again. The gravity feed, the air pressure feed, and the vacuum feed systems of fuel supply are all used on motor boat engines, and these are identical with those used on motor car engines.

In small boats, the gasoline tank is often made to fit in the bow of the boat, and as this is higher than the carburetor the gasoline flows down by gravity. Where a larger supply of fuel is wanted a cylindrical pressed steel tank can be mounted on the boat back of the seat just as it is on a runabout car.

The regular float valve carburetor is used on motor boat engines, and the speed of the engine is controlled by a throttle, that is, by a lever which opens and closes the throttle valve. On large engines the flyball type of governor is used, and by means of it any speed desired can be kept up.

Electric Ignition Systems.-There are three kinds

of igniters used for firing the fuel charge of motor boat engines, and these are (1) the make and break, (2) the jump-spark coil, and (3) the magneto sys

tem.

The make and break scheme of ignition is used on single cylinder engines. Where a make and break coil is used the timer is worked by an eccentric on the camshaft. It is preferred to a high tension system, as it is not as easily short-circuited by water.

The jump-spark coil system is practically obsolete on motor boat engines, the more positive and less troublesome magneto having all but superseded it.

The Oiling Systems.-On small engines grease and oil cups are used to lubricate the piston and crankshaft. These cups have been described and pictured in Chapter III. The larger engines are oiled by the splash and force feed systems, as explained under the heading of Motorcycle and Motor Car Gasoline Engines.

The Engine Cooling System.-Since a constant supply of cold water is always at hand for cooling a motor boat engine a radiator is not needed. The water is pumped from that on which the boat rides, through an intake pipe that connects the supply with the jacketed cylinders, and it flows out of the latter back to the supply by an outlet pipe.

Kinds of Pumps Used.-There are three kinds of pumps used on motor boat engines, and these are (1) the ordinary piston, or plunger pump; (2) the centrifugal pump, and (3) the gear pump.