Page:Motors and motor-driving (1902).djvu/185

Rh connection with the other end of the armature-winding, through the metal of the engine. When the moment of firing arrives the striker is caused to drop smartly on, causing  to separate from. At the same moment the shield E assumes such a position with regard to that a current is induced in the windings on, and being conducted through the connecting wire, a spark is caused to pass between the points of  and  igniting the charge in the engine.

. (1) Failure of Insulation. The stud which is brought through the wall of the combustion chamber has to be most carefully insulated from the metal flange in which it is placed. If this fails, the current will jump across to the frame of the motor in a similar manner to that of a broken sparking plug. The insulation is very liable to be burnt, and great care is necessary to make it good again. Thin washers of mica are used, but the intense heat generated in the interior of the combustion chamber appears to quickly affect it.

(2) Failure of Magnets.—After considerable use, the magnets are liable to lose their magnetism, thereby reducing the intensity of the spark. The only remedy is to return them to the makers to be re-magnetised.

(3) Faulty Adjustment.—It is obvious that the position of the shield at the moment of firing must be absolutely accurate, and when it is remembered that the working parts of this whole apparatus are moving at the rate of 350, or more, oscillations per minute, it may be seen that considerable wear is likely to take place, with the result that the parts get out of adjustment. The diagram opposite shows the relative position of the various parts, and, to assist the novice in accurately adjusting them, the following instructions are appended:—

Remove the top plate of the magneto machine by unscrewing tin- screws at the corners; the moving parts of the machine will then be open for inspection. Turn the engine gently round till the ignition point is reached, i.e. when the ignition rod drops, observing carefully the direction in which the oscillating