Since all the parts of the engine follow a regular sequence of operation, only the position of the piston and valves in the No. 1 cylinder need be considered in this process, and the three remaining cylinders may be practically disregarded. There are numerous methods, varying in their degree of accuracy, for locating the position of the engine pistons, but the most dependable one is that of removing the cylinder head so as to expose the pistons and valves to full view. With the head thus removed, the engine should be cranked slowly by hand until the No. 1 piston has risen to the top of its compression stroke and has just started to descend on its combustion stroke. At this moment the spark, when fully retarded, should normally occur in No. 1 cylinder.
Under circumstances where it is not convenient or desirable to remove the cylinder head the following approximate method for determining the location of No. 1 piston may be employed with a fair degree of success. Open the cocks of the priming cups on all the cylinders, and crank the engine slowly by hand until the No. 1 piston has just reached the top of its compression stroke. This can be ascertained by holding the thumb over the No. 1 priming cup and noting carefully the moment when the compression ceases to increase. After locating the dead center position of No. 1 piston in this way, turn the crank shaft a very slight distance further until the No. 4 exhaust valve is just at the point of closing. Under these conditions, provided the No. 4 exhaust valve lifter is in correct adjustment, the No. 1 piston should be approximately in the desired position of 5 engine degrees beyond dead center.
With the No. 1 piston thus carefully set in accordance with one of the above methods, preferably the former, bring the distributor into the position of full retard. To do this, disconnect the manual control attachment and turn the break-box as far as it will go in the direction in which the vertical shaft rotates. Then after making sure that the ignition switch is turned off, remove the distributor-head and the distributor rotor and the breaker box, and with a broad bladed screw driver back off the breaker cam nut until the cam is free to turn on its shaft. Next, replace the rotor temporarily, and turn the cam slowly until the breaker contacts just begin to open when the rotor occupies the position where it normally makes contact with the No. 1 distributor terminal. This adjustment can be made to the best advantage by turning the cam forward to separate the contacts then back again slowly until the contacts just come together, at which point the cam should be allowed to remain.
After the proper setting has thus been obtained, remove the rotor again and lock the cam securely in position by tightening the slotted nut that holds it. Finally, replacing the rotor, rock the vertical shaft backward and forward as far as the slack in the gears will permit, and note carefully the action of the break contacts. The setting of the cam must be so accurate that when the gears are rocked forward to take up the slack, the contacts will be just held apart and yet when the gears are rocked backward as far as the slack permits, the contacts will be actually closed.
A convenient method of verifying this adjustment is to turn on the ignition current and connect an ordinary 14 or 16 volt 2. c. p. lamp across the two binding posts of the breaker box. The lamp thus attached, will serve as a sensitive indicator for representing the action of the contact-points when the vertical shaft is rocked forward and backward to take up the slack in the gears. The moment the contacts begin to be separated, the lamp will light; but as soon as they are allowed to come together the lamp will at once go out again.
Should the test prove the first setting to be inaccurate, the cam must be readjusted, and the test repeated several times if necessary until the correct setting is finally obtained. Too much care cannot be employed in making this adjustment, because even a very slight inaccuracy in the setting of the cam will produce a considerably magnified effect upon the operation of the engine. This is due to the fact that the engine speed is twice as great as that of the vertical shaft.
General Care.—Under normal operating conditions the ignition system requires very little care aside from the usual precautions against moisture and dirt. There are, in fact, but three points of importance that need attention during service:
1. Lubrication.
2. Cleaning and adjustment of the breaker contacts.
3. Inspection of the wiring and the spark plugs.