On the cheaper makes of motorcycles the jumpspark coil system is used, while the better makes are equipped with the high-tension magneto-system. The jump-spark-coil system and the high-tension system used on motorcycle and other mobile engines work on the same principle as those described in connection with gas engines.

FIG. 42-B. PERSPECTIVE OF A STROMBERG CARBURETOR

The Ignition Timing System of a Multi-Cylinder Engine.-Where a jump-spark igniter is used on a single cylinder engine a timer, or interruptor, as it is called, is used to make and break the primary circuit, as previously explained, but where two or more cylinders must be fired successively a revolving timer, or distributor, as it has been named, is employed.

A distributor consists of a disk around which are fixed as many metal contact segments as there are cylinders to be fired, and each segment is connected by a wire with a spark-plug, as shown at A in Fig. 43.

A metal contact arm is pivoted to the center of the disk and the former makes contact with some

FIG. 43-A. A DISTRIBUTOR FOR TIMING THE IGNITION OF A FOUR CYLINDER ENGINE

part of the engine, that is, it is grounded, so that it will form a connection with the spark-plugs.

The contact arm is turned by the camshaft and makes one complete revolution to every two revolutions of the crankshaft. Now every time the arm makes contact with one of the segments of the disk a spark takes place between the electrodes of the

spark-plug that is connected with that particular segment all of which is clearly shown at B.

A lever is attached to the disk of the distributor and goes up to a control lever on the handle-bar, so that the disk can be moved ahead or set back, when the spark will be advanced or retarded, as the case may be.1

FIG. 43-B. WIRING DIAGRAM OF A HIGH TENSION JUMP-SPARK MAGNETO, INTERRUPTER AND DISTRIBUTOR FOR A FOUR CYLINDER ENGINE

Kinds of Lubricating Systems.-There are two schemes used for oiling motorcycle engines, and these are (1) the splash system and (2) the force feed sys

tem.

1 The theory of advancing and retarding the spark is ex plained in Keeping up with Your Motor Car by the present author and published by D. Appleton & Co., New York.

FIG. 44. THE SPLASH LUBRICATING SYSTEM OF A FOUR

it is fed into it from a tank by gravity, or (3) it is forced into it from a tank by a pump.

The oil is then splashed into the cylinder and onto the connecting rod bearings by little scoops, or spoons, fixed to the lower ends of the connecting rods which dip into the oil. It is shown in Fig. 44.

The Splash System. This is a simple system for oiling the working parts of a mobile internal combustion engine but it must be looked after rather closely. In this system the oil is (1) poured into the crank-case through an opening called a breather; (2)

CAM SHAFT
BEARING

MAIN
BEARING

The Force Feed System.-All the finer makes of mobile engines for all purposes use the force feed system of lubrication, or mechanical oilers as they are sometimes called.

In this system the oil is put into a well in the bottom of the crankcase, or sump as it is called, and from there it is forced by a pump worked by the en

gine through an oil tube above and parallel with the crankshaft.

From this tube the oil is forced or flows through ducts, or holes, in the crank-webs to the crankshaft bearings, on through to the crank-pins and through hollow connecting rods to the wrist-pins. The pistons are kept lubricated by the oil that runs out and which is thrown from the lower ends of the connecting rods. The whole scheme is shown in Fig. 45.