These magnetos are of the rotating magnet type, that is, the magnet system revolves, while the less robust parts, such as the winding and condenser, are stationary, and the contact breaker does not rotate, so that these parts are not subjected to mechanical stresses.

Some magnetos are fitted with an ignition switch which provides a means of stopping the engine, while with other types provision is made for the ignition switch to be situated remote from the magneto.



Although a magneto should not be dismantled or interfered with unnecessarily, a little periodical attention to the ignition system is essential if it is to give its best performance.



CAM. The cam is lubricated by a felt pad. About every 100 hours running inspect the pad, and if it is dry, apply a few drops of thin machine oil.
CONTACT BREAKER PIVOT. About every 25 hours running place a very small amount of clean engine oil on the contact breaker pivot. This is accessible when the cotter pill and washers are removed. Do not allow any oil to get on or near the contacts.



The magneto has, in many cases, to work under conditions where it is exposed to dirt and moisture. Although the design of the magneto is such that it cannot gain access to the interior, an accumulation of wet and dirt on the insulating surfaces of the plug, cable and high tension terminal will tend to cause bad starting.

It is advisable therefore to wipe these parts with a clean dry cloth occasionally. Next examine the contact breaker; the contacts must be kept clean. If necessary, polish then with fine carborundum stone or very fine emery cloth, and afterwards wipe with a cloth moistened with petrol. To render the contacts accessible remove the cotter pin and nut securing the contact breaker lever and spring. The lever and spring can now be lifted off their locating pins, taking care not to lose the collars and washers. The metal and fabric washers must be re-fitted in the correct order.

The cam must be clean and free from any deposit; a cloth moistened with petrol should be used for, cleaning.



Check the gap between the contacts by turning the engine over slowly until the contacts are fully opened, and then insert the gauge provided in the gap. If it is correct the gauge should be a sliding fit. Do not alter the setting unless the gap varies considerably from the gauge. If adjustment is necessary, keep the engine in the position to give maximum opening of the contacts and slacken the two locking screws in the contact breaker base (do not slacken the screw nearest the felt pad). Then insert screwdriver in slot provided and lever the bracket carrying the contact until the gap is set to the thickness of the gauge. Afterwards tighten the locking screws. It is advisable to check the gap again to ensure that no movement has taken place.

The correct gap should be .010 to .012 in. (0.25 to 0.3 mm.).


Replacement of high Tension Cable.

If, on inspection, the high tension cable shows signs of perishing or cracking, it should be replaced. Replacement cable must be 7 mm. rubber-covered ignition cable.

The method of connecting the cable is as follows: Remove moulded cover by unscrewing the two securing screws, unscrew the cable fixing screw oil the inside of the cover, push the cable, which must be cut off flush to the correct length, well home into its terminal and then tighten the screw, which will pierce the insulation to make contact with the cable core.



The magneto has been correctly timed by the engine makers before despatch, and should not be interfered with unnecessarily. Should it, however, be necessary to re-time the magneto, the procedure stated in the engine instruction book must be adopted.


Sparking Plug.

The plug electrodes burn away slightly in service, and thus in time the gap length increases. Occasionally examine and clean them, adjusting them if necessary to the right setting. The gap between the points should be normally .020 in. (.5 mm.), and should never exceed .025 in. (.6 mm.).



If a failure of the ignition is suspected, unless the cause is at once apparent, the reader is strongly recommended to proceed in accordance with the following routine, which should quickly enable him to locate the trouble.

If misfiring occurs, either the plug lead or the plug may be at fault. An examination of the high tension cable may reveal the fault; the rubber may show signs of perishing or cracking; it will not last for ever. If a spare plug is at hand, it may be substituted, or if it is merely the gap that is too large, it may be adjusted (see page 3). Missing with full throttle is sometimes due to the plug gaps being- too wide. Bad plug insulation is sometimes caused through sooting, and occasionally may be remedied by washing the plug. out with petrol.

It is sometimes recommended to remove the plug and, allowing the body to rest on the cylinder head, to observe whether a spark occurs at the points when the engine is turned by hand.

If the fault is not yet apparent, remove the contact breaker cover, and with the engine slowly turned by hand, examine the action of the contact breaker rocker arm; it is possible that the arm is not answering to its control spring, and is remaining permanently open as the cam is rotated. If this appears to be so, remove the contact breaker lever as described on earlier, and examine the pin on which the lever works. If necessary, clean the pin with fine emery cloth, wiping away all grit and moistening with grease, before replacing the lever. No trace of grease should be left anywhere near the contacts after this has been done.

If the magneto has recently been replaced, it is possible that it may have been timed incorrectly. Timing is by no means a simple matter to remedy, and it is advisable to have it done by a skilled mechanic.

If, after exhausting the above scheme of inspection, there is still any doubt or difficulty about the ignition system, it is little use continuing the examination. The magneto should not be further dismantled, but returned to the Works or nearest Service Depot.