Four Cycle Motors

The four cycle cylinder has both the intake and exhaust openings at the top of the cylinder, and they and operated automatically by valves instead of by the piston as in the two cycle. To explain, we will follow the operation. Commencing with the piston at the top of the cylinder, the down stroke of the piston draws in a charge, the inlet valve being open and the exhaust closed. At the end of the down stroke of the piston the inlet valve closes and the up stroke of the piston compresses the charge, which is exploded driving the piston down. At the end of this down stroke of the piston the exhaust valve opens and the up stroke forces the exhausted charge out. At the end of this up stroke the exhaust valve closes and the inlet valve opens, ready to repeat the operation.

The argument in favor of the four cycle is that the cylinder is better cleared of the exploded charge before the fresh charge enters. This is not entirely true for the reason that the piston does not travel clear to the top of the cylinder, therefore the compression or firing chamber may still retain a portion of the exploded charge.

This is the most important factor in the operation of the motor. There are several forms of ignition in use. First, the hot tube method, a device but little used by manufacturers in this country except for stationary motors using natural gas, so we will not trouble to describe it.

All electrical sparking devices are supplied with electricity, either from the cells of a battery or a small dynamo. As the latter will not generate the current uutil in motion it is always necessary to have the battery to start the motor. After the motor is in motion the bttery is switched off and the current supplied by the dynamo only. This results in saving the battery and is in all ways most satisfactory. This is particularly true in reference to the larger motors.

The electrical sparking devices may be divided into two classes. The first class consists of the the jump spark. The second class may be classified under three heads, the make and break, the wipe spark and the hammer break.

The jump spark is becoming the most popular method and is fast superseding all the others for two cycle motors. The jump spark mechanism consists of three or four dry cells, an induction coil with a primary and secondary winding fitted with a vibrator (commercially known as a spark coil), a spark plug and a suitable device attached to the shaft for making the circuit. The spark plug screws directly into the firing chamber and contains the points orterminals. These are properly insulated and at their end are not more than 1-16 inch apart. Without technical explanation it may be stated that when the circuit is formed the excitement of the coil causes a strong spark to jump between the terminals of the spark plug within the firing chamber.

The points in favor of the jump spark are less moving parts, positive ignition, simplicity of mechanism and no moving parts within the firing chamber.

The objection to the jump spark is that the space between the terminals is liable to become fouled by soot ifthe vapor is too rich in gasoline or by oil if too much lubrication is given the cylinder. However, the objectional conditions seldom occur after one becomes familiar with the requirements of the motor, and when the points do become fouledthe spark plug may be instantly removed and cleaned.

The second class, the make and break, wipe spark and hammer break all operate on the same principle with numerous different mechanical methods of operation. Therefore, we will not attempt any definite description other than to state that they consist of two electrodes or terminals within the firing chamber. One of these is stationary and one movable. The spark is given by the separation of the terminals. When the points lap by and wipe together it is called a wipe spark; when separated by a spring it is called a make and break, and when separated by a blow from a projecting arm it is called a hammer break. Of the three, the make and break is most in favor. The objection to all of these is the mechanism required and its liability to get out of order; that the firing chamber is twice punctured by the electrodes; that it is difficult to keep the joint tight where the moving electrode enters the firing chamber; that it is hard to lubricate - this for for the reason that the pressure within tends to force back the oil; that the points of the terminals wear out and are apt to become fouled or gummed with oil and soot.

Although our experience is in favor of the jump spark, especially with the smaller types of motors, we must, in justice say that some of the make and break devices give splendid satisfaction, particularly when used on the larger multiple cylinder motors.