MAGNETO TROUBLES
If the ignition fails, and the question arises as to the reason, the condition of the magneto may be tested quickly and in a most satisfactory manner. It either gives a current or it does not, and to learn its condition it is only necessary to disconnect it from the ignition system, and to connect one end of a length of wire to its terminal. Holding the free end of this wire in the bare fingers of one hand, and cranking the engine with the other hand, also bare, a shock will be felt as the armature revolves, if it is in good condition. If this test is too strenuous, the free end of the wire may be held lightly against the teeth of a gear while an assistant cranks the engine briskly. As the wire falls from tooth to tooth, a time will come when the point of maximum current coincides with the breaking of the circuit at the gear, and if the magneto is in good condition, a flaming spark will appear.
There is little about a magneto of the type described to get out of order. Oil or dirt between the spring or brush and the end of the conducting rod may prevent the flow of current, or, what is more unlikely, the wire of the armature may be broken. The last trouble is of rare occurrence, for when winding the wire on the armature it is shellacked, and for all practical purposes the whole becomes a solid mass. The only point where the wire can break is the half-inch of it that is connected to the inside end of the conducting rod that passes through the shaft, and the condition of this may be learned by removing the dust cover and looking. If broken, a drop of solder, carefully applied, will repair the damage.
A question that is frequently asked is regarding the liability of the field magnets to lose their magnetism. If made of the proper material, and handled and used under proper conditions, they should hold their magnetism indefinitely. The strength of a toy magnet may be increased by tearing its keeper sharply away from the poles, and as sharply replacing it, the operation being repeated. When the armature of a magneto revolves, it performs the same office for the field magnets, and it has the effect of keeping them up to strength indefinitely. If the magneto is mishandled, however, it is another story, and an inquisitive or careless worker can almost instantly weaken a field by removing the armature without taking the proper precautions. The armature, when in position, acts as a keeper, and provides a path of low resistance for the passage of the lines of magnetic force. If the keeper is taken away, the lines of force are required to traverse the higher resistance of the air, and many of them then being overcome, their number decreases and the field becomes greatly weakened. This takes place instantly on the removal of the armature. It is rarely necessary for a chauffeur to remove the armature of a magneto, but when it is required, the first step is the placing of a heavy plate of iron under the arch of the magnets, and in close metallic contact with the pole pieces, the dust plate being removed. This will act as a keeper, and the armature may then be removed. If such a plate of iron is not at hand, both of the end plates may be unscrewed and one of them removed, and then, as the armature is drawn out slowly, small steel tools, or short lengths of iron rod, well cleaned, may be fed in after it, so that the cavity is well filled. If these precautions are taken the armature may be removed with safety, but it is better not to attempt this, and it is never advisable to detach the magnets from the base or pole pieces. So much damage may be done to a magneto by an unskilled man, that some of the manufacturers go to the length of equipping their magnetos with seals, the breaking of which is evidence that the machine has been tampered with, and that someone is directly to blame if it does not deliver current.
When an engine is equipped with a double system of ignition, or when there are two sources of current, one being a magneto, the greatest care must be taken to prevent even the momentary flow of the battery current through the armature winding, for this will result in the demagnetization of the field. The same trouble will result if the magneto current is led through the winding of a primary induction coil in the hope of intensifying the current. Should the battery current flow through the armature winding, the core would be magnetized, for it would then be an electro-magnet, and the magnetic field set up by the armature under such conditions would overcome the less powerful field set up by the field magnets and their strength would instantly be reduced.
It is very essential to keep the armature bearings thoroughly lubricated in order that there may be as little wear as possible. The clearance between the armature heads and the pole pieces is so slight that a trifling amount of wear in the bearings would permit the two to rub or strike. The best magnetos are equipped with ball bearings, provided with wick feeds that keep them lubricated, but even with these the lubrication must be watched. Oil cups are provided, which must be kept filled, but it must be remembered that an excess of oil may make trouble in working its way into the armature winding and destroying the insulation. In some cases the oil cups are provided with an overflow, which prevents excessive oiling and the collection of surplus oil around the bearings.