THE REPAIR AND UPKEEP OF MAGNETOS.
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An Appeal for Specialization in the Treatment of these Valuable Components and Notes on Points Which Require Attention.
SLOWLY, but none the less surely, large road transport concerns are realizing the necessity for providing a special department for the care and maintenance of magnetos. In the very recent past, almost without 'exception, the fitter who repaired the back axle was the same man who overhauled the ignition apparatus. There is little doubt that this practice was the primary cause of so many magneto failures. The repair and maintenance of these little machines is essentially an electrical job.
It is rather a curious fact, but none the less true, that if an ordinary 200-volt electric drill failed in the workshop it would be sent to a specialist for repair; but if one of the magnetos failed—and this, by the way, has to work at a potential of about 10,000 voits—it would probably be given to cne of the engine fitters, and he would be expected to make a good job of it in about half an hour.
When it is realized what work these small machines have to do, and the abuse they generally get, it is little short of marvellous that they function at all.
Obviously, it would not be a practical proposition for a company owning about 20 vehicles to employ a skilled magneto fitter and install the necessary plant and testing instruments for his use. The alternative is, not to allow the engine fitters to repair them, but to keep two or more spare machines to replaceany that may become defective, and then to send the defective ones to a reputable firm of repairers.
Where the number of vehiclea warrants it, a special bench should be set apart for this work, or, if large enough, a special department suitably equipped. It should be remembered that it is not the initial cost of the repair that matters F50 much as the inconvenience to customer or passengers should the magneto fail on the road, with the resultant loss of time and temper.
Viewing this from a passenger transport company's point, it is absolutely essential. to maintain regular services with a minitritun number of failures and consequent lost miles. To accomplish this the magnetos must be kept at the highest possible standard of efficiency, and drivers and running shift men should only be allowed to change a defective machine for a good cite.
A very common mistake made by running shift men, often perhaps to save time, is.that, if they have to attend a break-. down Caused by magneto failure and find the contact-breaker defective, instead .of changing the machine for the spare they are carrying they -will merely change the contact-breakers.
Now, from a strictly mechanical standpoint, this would not appear to be,a very grave crime; but, as every contactbreaker must be adjusted to suit its own particular machine, it is obviously very bad practice.Of course, all contactbreakers of the ,sarrie type are probably standard when the machines are new, but after -six months' service each must be adjusted to its own standard to obtain the greatest efficiency.
Another malpractice is the changing of one magneto for another with the exception of the distributor board. The distributor of the old magneto is usually left hanging from the hth-tension cables and then the new magneto coupled to it. With the carbon-brush type of distributor perhaps this is not a very grave fault, but it is absolutely fatal to
_ the series spark type. Magnetos of this type have been observed trying to do their job with a series spark gap of approximately 5 ram. at the distributor segments, brought about by the indiscriminate changing of distributor boards.
In the ease of a concern which undertakes itg own repairs, it is of paramount importance that only spare parts of the best manufacture are used. It must be admitted that numerous magneto spares are offered for sale that are not worth the room they occupy in the stores. Components which require special attention when purchasing are rewound armature pores, condensers, bearings, all moulded insulators and platinum contacts. In nearly every case, unless the magneto repairs depart
ment is very well equipped, one has to depend on the integrity of the supplier as to whether his product has passed the necessary tests. Rewound armature cores should be capable of delivering at least a 10 rem. spark for 10 mine.
Condensers should have their capacity and the dielectric test voltage marked on them.
All moulded insulators should be guaranteed to have been tested in oil at a voltage of at least 30,000 for 2 mins.
Platintim contacts should be purchased to specification with regard to the percentage of iridium in the alloy. It is only by strict observance to these conditions that one can obtain really good magneto efficiency.
Until very recently a constant source of trouble was the swelling of the bearing bush of the lever in the contactbreaker. This was ustiallY made of fibre, and, although perhaps thoroughly impregnated with wax, could not be trusted implicitly. It is believed that a material has now been found which overcomes this defect.
We are told that "cleanliness is next to godliness." In magneto work cleanliness also makes for increased efficiency. Any machine generating thousands of volts cannot be expected to give satisfactory results if the armature, collecting rings and gearwheels are covered in .a sticky mixture of grease and carbon dust. Nfachines should' lit cleaned thoroughly and as frequently as Possible. If more than one machine is being cleaned at any one time, each must be dismantled as a separate unit and the various components 'confined to the tray or box allotted to that particular machine.
The small amount of time that might be saved by dismantling a number of machines together and cleaning all the parts on a mass-production basis is soon lost in, the fitting that is necessary to the changed components. Finally, with regard to running shift reports on breakdowns, do not be content with the curt diagnosis, "magneto trouble." Ask for an explanation as to why the machine failed. It is not uncommon for an engine to have two or even three magnetos fitted to it before the defect is discovered somewhere else,