In its simplest form the timer consists of a cam mounted on the camshaft; the cam presses against a spring which is fixed at one end and has a contact point on its free end. When the corner of the cam strikes the spring it presses it against the stationary contact and this closes the primary circuit.
The spark-plug, see B and C, is simply a metal tube with threads on the outside to permit it to be screwed into the head of the cylinder and inside of which a porcelain tube is fixed. A heavy wire is secured inside of the porcelain tube, one end termi nating in a binding post and the other end projecting out of an inch. To the lower part of the metal plug another heavy wire is soldered and the ends of these two wires form a spark-gap about of an inch long, and they are connected to the ends of the secondary coil, as shown at A.
It is not necessary to use a wire to make a con nection between the metal parts of the spark-plug and the secondary coil. Instead, what is called a ground is used, that is, the metal part of the spark plug makes connection with the iron of the engine, and hence all you need to do to complete the circuit is to fix the other end of the secondary coil to any part of the engine where it is convenient to do so.
The High Tension Rotating set up currents whose tension is high enough to make a jump spark with a magneto the armature must have two coils of wire wound on it just like the battery spark coil above described.
In this kind of a magneto when the armature ro tates the primary coil on it sets up low tension cur rents so that no battery is needed, and these currents induce high tension currents in the secondary coil which is wound around it. Different from a spark coil, though, one end of the primary coil is con nected to the iron core of the armature, that is, it is grounded, and the other end of the secondary coil is connected to a brush which presses on a slip-ring; in this way only one ring and one brush are needed, as shown at A and B in Fig. SO. A cross-section of a high tension magneto is shown at B and the magneto complete at C.
Where a stationary engine has two or more cylin ders it is the usual practice to provide each one with a complete ignition system so that in this way they work independently of each other.
Governors and How They types of governors are used for keeping the speed of the engine steady, and these are (1) the hit and miss governor and (2) the throttling governor.
The Hit and Miss Governor.—It is so called be cause it allows the cam to open the gas inlet valve when the engine tends to slow down and keeps the valve closed when the engine begins to run too fast. If the load is at all variable the engine will very often miss firing its fuel charge and then perhaps fire it several times in succession.
How the Governor is Made.—There are many dif ferent forms of this type of governor, but a good and simple one is that used on the Otto engine, and this will serve to show the principle on which the others work.
It consists of (1) a pair of flyballs; (2) a conical weight to hold (3) the governor shaft down; (4) a beveled gear on the lower end of the shaft to rotate the flyballs, and this gear meshes with (4) another beveled gear on the camshaft. On the shaft is (5) a sleeve with a groove cut in it, and in this sets (6) the forked end of a horizontal lever, to which is fixed (7) a vertical lever with a fork on its free end.
This latter forked lever straddles (8) a thin steel wheel called a gas roller, which is mounted on a roller shaft. Under the gas roller and on the cam shaft there is (8) a cam; the roller shaft, which is hollow, slips over (9) the pin of a crank, or roller lever, as it is called, and finally this is fixed to (10) the gas valve lever, the arm of which rests on the end of the gas valve poppet, all of which are shown at A and B, in Fig. 81.
The Way It Works.—When the engine is running the balls are rotated by the vertical shaft by means of the beveled gears and the weight tends to hold the shaft down against the centrifugal force which makes them fly apart.
When the balls spread apart they lift up the grooved sleeve and, as the :fork of the horizontal lever rests in the groove, it moves up with it; in turn this moves the vertical forked lever, which is fastened to it sidewise. When this action takes place the fork slides the roller over and makes it miss the cam on the camshaft.