Motor-car principles; the gasoline automobile

by Roger B. Whitman

Any interference with the regular running of an automobile is usually due to engine trouble, and the nature of the irregularity or the unfamiliar noise will often give a clew to the experienced driver by which the fault may be located. When the engine shows that something is wrong, it is of little use to guess at the cause, for changing an adjustment without being sure that it is the right thing to do will probably add to the difficulty instead of remove it. The laying out of a system for the location of a fault is not difficult, and its application simplifies matters when trouble is encountered. By following a process of elimination, the condition of the different parts of the mechanism can be learned, and if on test the ignition system proves to be operating correctly, the production of the mixture may be considered to be guilty until that in turn is shown to be innocent.

MAKE-AND-BREAK IGNITION

An engine equipped with the make-and-break ignition system is always provided with a conducting bar across the top or side of the cylinders, called a bus bar, connected with the source of current, and each igniter is connected to it through a switch. If one of the cylinders fires regularly, it is an indication that the current is being generated properly, and that no time need be wasted in examining the generator. By means of the switches, the igniters may be tested individually by cranking the engine with one switch closed and the others open. When the clutch is disengaged the engine should run on one cylinder, and if this is the case, the igniter on the line of the closed switch is shown to be in good condition. The opening of this switch and the closing of the next will give a comparison when the engine is again cranked, and if explosions occur, the igniter points may be adjusted until the two cylinders work equally well. If the cylinder does not operate, the stationary igniter point should be withdrawn and its contact examined; this should be bright and clean. The movable point should be worked by hand, to determine whether the joint is stuck or the spring weak or broken.

If none of the cylinders show signs of explosions, the connections should be examined to make sure that they are secure. On systems employing a magneto alone, the wiring consists of a single wire from the magneto to the bus bar, and the shorter wires from there to the igniters. These wires are clearly visible, and any loose connections or broken wires may be detected without difficulty. If the connections and wiring are in good condition, the fault may be located in the magneto, or, if it has recently been dismounted, its incorrect setting in relation to the crank shaft. (See Appendix.)

If the ignition system proves to be in proper working order, attention may be paid to the carburetor and its connections.

JUMP-SPARK IGNITION

In testing an engine fitted with the jump-spark ignition system, the circuit should be closed and the crank shaft revolved twice, attention being paid to the sound of the vibrators. On a four-cylinder engine, the timer makes four contacts in two revolutions of the crank shaft, and if all of the vibrators are heard it is proof that the primary circuit is in good condition, and not the seat of the trouble. If only one of the vibrators buzzes, the battery circuit may be considered to be working properly, for otherwise no current could have passed to the coil box. The trouble may then be identified as being in part if not altogether in the adjustment of the vibrators of the dead coils, their connections with the timer, or in the timer itself. One end of a short piece of wire should be touched to the timer binding post of one of the dead coils, and the other to any metal part of the engine, the lubricator, for instance, to form a short circuit through the primary circuit with the exception of the timer and its connections. If the vibrator buzzes, the trouble is not in the coil, but in that part of the circuit cut out by the short-circuiting wire. The same piece of wire may be used to bridge across to any metal part of the engine from the binding post on the timer at which the wire from the coil is connected, and if the wire from the coil to the timer is in good condition, the vibrator will again buzz, showing that the fault must be in the timer, for all other parts of the primary circuit of that particular coil have been proven to be working correctly. A dirty or faulty contact in the timer, or a loose connection, will probably be the cause.

If the primary circuit is shown to be in good order, attention may at once be given to the gasoline feed, for while the secondary circuits have not been tested, it is extremely unlikely that the spark plugs or their connections will prove defective on all four cylinders at the same time.

THE CARBURETOR

Touching the primer of the carburetor will show whether the gasoline flows to the float chamber, for if it is present it will spurt out of the opening through which the priming stem passes. If the air inlet is so arranged as to permit it, gasoline dropping out of it when the carburetor is primed excessively indicates that the liquid flows out of the spray nozzle, this part thus being shown to be clear. If no gasoline shows around the priming stem, the feed pipe or float valve may be suspected of being clogged, it being taken for granted that there is gasoline in the tank and that the supply cock is open. If it is found that gasoline is present in the air inlet, and that the carburetor is damp with it when the primer has not been touched, it indicates that the float chamber is flooded; the carburetor should be taken apart for inspection and thorough cleaning.