LOCATING TROUBLE
Trouble in the ignition system is indicated by the motor “missing,” stopping entirely, or by inability to start.
It is safe to assume that the trouble is not in the magneto, and the carburetor, gasoline supply and spark-plugs should first be investigated.
If the magneto is suspected, the first thing to do is to determine if it will deliver a spark. To determine this, disconnect one of the high-tension leads from the spark-plug in one of the cylinders and place it so that there is approximately 1⁄16′′ between the terminal and the cylinder frame.
Open the pet cocks on the other cylinders to prevent the engine from firing and turn over the engine until the piston is approaching the end of the compression stroke in the cylinder from which the cable has been removed. Set the magneto in the advance position and rapidly rock the engine over the top-center position, observing closely if a spark occurs between the end of the high-tension cable and the frame.
If the magneto is of the dual type, the trouble may be either in the magneto or in the battery or coil system, therefore disconnect the battery and place the switch in the position marked “MAG.” The magneto will then operate as an independent magneto and should spark in the proper manner. After this the battery system should be investigated. To test the operation of the battery and coil, examine all connections, making sure that they are clean and tight, and then with the switch, in the “BAT,” rock the piston slowly back and forth. If a type “VN-1” coil is used, a shower of sparks should jump between the high-tension cable terminal and the cylinder frame when the piston is in the correct position for firing. If no spark occurs, remove the cover from the coil and see that the vibrating tongue is free. If a type “N-1” coil is used, a single spark will occur. The battery should furnish six volts when connected to the coil, and this should also be verified.
If the coil still refuses to give a spark and all connections are correct, the coil should be replaced and the defective coil returned to the manufacturer.
If both magneto and coil give a spark when tested as just described, the spark-plugs should be investigated. To do this, disconnect the cables and remove the spark-plugs. Then reconnect the cables to the plugs and place them so that the frame portions of the plugs are in metallic connection with the frame of the motor. Then turn over the motor, thus revolving the magneto armature, and see if a spark is produced at the spark gaps of the plugs.
The most common defects in spark-plugs are breaking down of the insulation, fouling due to carbon, or too large or small a spark gap. To clean the plugs a stiff brush and gasoline should be used. The spark gap should be about 1⁄32′′ and never less than 1⁄64′′. Too small a gap may have been caused by beads of metal forming due to the heat of the spark. Too long a gap may have been caused by the points burning off.
If the magneto and spark plugs are in good condition and the engine does not run satisfactorily, the setting should be verified according to instructions previously given, and, if necessary, readjusted.
Be careful to observe that both the type “VN-1” and type “N-1” coils are so arranged that the spark occurs on the opening of the contacts of the timer. As this is just the reverse of the usual operation, it should be carefully noted when any change in the setting of the timer is made. The timer on the dual type magneto is adjusted so that the battery spark occurs about 5° later than the magneto spark. This provides an automatic advance as soon as the switch is thrown to the magneto position “MAG.” This relative timing can be easily adjusted by removing the interrupter and shifting the cam in the direction desired.
Fig. 66.—The Dixie Model 60 for Six-Cylinder Airplane Engine Ignition.
THE DIXIE MAGNETO
The Dixie magneto, shown at [Fig. 66], operates on a different principle than the rotary armature type. It is used on the Hall-Scott and other aviation engines. In this magneto the rotating member consists of two pieces of magnetic material separated by a non-magnetic center piece. This member constitutes true rotating poles for the magnet and rotates in a field structure, composed of two laminated field pieces, riveted between two non-magnetic rings. The bearings for the rotating poles are mounted in steel plates, which lie against the poles of the magnets. When the magnet poles rotate, the magnetic lines of force from each magnet pole are carried directly to the field pieces and through the windings, without reversal through the mass of the rotating member and with only a single air gap. There are no losses by flux reversal in the rotating part, such as take place in other machines, and this is said to account for the high efficiency of the instrument.
Fig. 67.—Installation Dimensions of Dixie Model 60 Magneto.
Fig. 68.—The Rotating Elements of the Dixie Magneto.
And this “Mason Principle” involved in the operation of the Dixie is simplified by a glance at the field structure, consisting of the non-magnetic rings, assembled to which are the field pieces between which the rotating poles revolve (see [Fig. 68]). Rotating between the limbs of the magnets, these two pieces of magnetic material form true extensions to the poles of the magnets, and are, in consequence, always of the same polarity. It will be seen there is no reversal of the magnetism through them, and consequently no eddy current or hysteresis losses which are present in the usual rotor or inductor types. The simplicity features of construction stand out prominently here, in that there are no revolving windings, a detail entirely differing from the orthodox high-tension instrument. This simplicity becomes instantly apparent when it is found that the circuit breaker, instead of revolving as it does in other types, is stationary and that the whole breaker mechanism is exposed by simply turning the cover spring aside and removing cover. This makes inspection and adjustment particularly simple, and the fact that no special tool is necessary for adjustment of the platinum points—an ordinary small screw-driver is the whole “kit of tools” needed in the work of disassembling or assembling—is a feature of some value.
Fig. 69.—Suggestions for Adjusting and Dismantling Dixie Magneto. A—Screw Driver Adjusts Contact Points. B—Distributor Block Removed. C—Taking off Magnets. D—Showing How Easily Condenser and High Tension Windings are Removed.
With dust- and water-protecting casing removed, and one of the magnets withdrawn, as in [Fig. 69], the winding can be seen with its core resting on the field pole pieces and the primary lead attached to its side. An important feature of the high-tension winding is that the heads are of insulating material, and there is not the tendency for the high-tension current to jump to the side as in the ordinary armature type magneto. The high-tension current is carried to the distributor by means of an insulated block with a spindle, at one end of which is a spring brush bearing directly on the winding, thus shortening the path of the high-tension current and eliminating the use of rubber spools and insulating parts. The moving parts of the magneto need never be disturbed if the high-tension winding is to be removed. This winding constitutes all of the magneto windings, no external spark coil being necessary. The condenser is placed directly above the winding and is easily removable by taking out two screws, instead of being placed in an armature where it is inaccessible except to an expert, and where it cannot be replaced except at the factory whence it emanated.