MAGNETO RETIMING

Sun (Auckland), Volume IV, Issue 1012, 1 July 1930, Page 7

MAGNETO RETIMING

the PROCESS summarised A Although drivers should not be en-j niiraeed to be tampering constantly it Sth engines and running gear, it has c. Xftea been found desirable for drivers, a“specially when engaged upon long o. journeys, to know how to retime a g “sometimes quite a simple trouble si may necessitate the removal of a mag- f. neto for a repair which is well within tl he driver's ability to remedy. 1' or t. example, a water hose connection a. breaks spreading water all over the m"iue After the joint has been re- o: paired the engine refuses to start he- h rau S e the magneto is saturated with i R water and cannot be dried out with- “ out removal and partial dismantling. | P Similarly, in a case of total magneto ; h breakdown, when a replacement mag-1 S neto is available, if the driver is able f to cope with the job of retiming, the trouble and consequent expense neces- 11 sitated by sending out a fitter are 0 avoided. , , , „ Haphazard methods are useless a when dealing with magnetos, but a u knowledge of the subject such as is siven here and attentiou to detail will b ensure success to operators who pos- J] sess merely elementary knowledge. the process summarised 1 Before attempting to fit a magneto to an engine it is necessary to knowcertain simple but essential facts about both the engine and the magneto. There are nine points which ! need consideration, and they can be | summarised briefly as follow:-—(1.) j Find the firing sequence of the cylinders. (2) Set the engine with No. 11 1 (front) piston at the top dead centre c

at the beginning of the firing stroke. ( 13) Note the direction in which the j distributor of the magneto will rotate. " (4) Retard the magneto. (5) Choose ( the most convenient terminal on the c block for locating No. 1 high-tension , lead as suggested by the direction in J which the distributor rotates. (G) ( Turn the distributor brush into con- j tact with the terminal thus chosen: j (7) Set the contact breaker with the , points barely opening. (S) Couple ; up and secure magneto. (9) Connect j the high-tension leads in their firing <. order to the distributor terminals as , served in turn by the rotating distribu- , tor. s FIRING ORDER AND TOP DEAD 1 CENTRE One point that must be discovered ' before the engine is set to receive the ! magneto is the firing sequence of the j cylinders: that is, the order in which ) the remaining cylinders will fire following No. 1. Four-cylinder engines, . have only two possible firing orders j and they are 1.3,4,2 and 1,2, 4, 3 1 respectively. If the firing order of the engine to be timed is not already known it can be found by turning over the engine and watching the action of the valves. Watch | No. 1 inlet open and close. Tho next inlet valve to open must be that on No. 2 or 3 cylinder. If it is on No. 2 cylinder the firing sequence is 1,2, 4,3, and if it is No. 3 the order will be 1,3, 4,2. These are the only possible combinations. The type of engine in general use today is the four-stroke engine. The strokes in their order are induction (suction), compression, power and | exhaust. The critical point when fitting j a magneto is that between the end of the compression stroke and the he-; ginning of the power or firing stroke. At this moment the piston is at top dead-centre. 'Phis position can bo found by getting someone to turn the j engine over slowly while the action ; of the valves of No. 1 cylinder is watched. After the inlet valve has opened and closed the piston will he approaching top dead centre on the stroke required. Top dead centre is usually marked off on the periphery of the flywheel, and the mark should be made to register with the pointer situated close by for the purpose. If the flywheel cannot be seen, insert a piece of wire through the sparking plug hole in No, 1 cylinder and feel for the piston moving upwards. When the piston is absolutely at the top of its stroke gently disengage the starting handle, exercising care not to rotate the crankshaft any further. The engine is now ready to receive the magneto, which in its turn must be set in the correct position to deliver a spark to No. 1 cylinder. THE ACTION OF THE CONTACT BREAKER The part of the magneto which determines the instant that the spark shall occur is the contact breaker. As this revolves a fibre brush, mounted on a bell-crank arm, strikes against a cam, causing the platinum contact Points to open. The moment they begin to open a high-tension electric current is produced in a circuit that includes the distributor block terminal which is then registering with the distributor brush. The platinum contact points open twice during every revolution of the contact breaker. Thus two complete revolutions are required to supply each of the four contacts on the distributor block, whence the current is carried by way °f the high-tension cables to the respective plugs of the cylinders. The contact breaker setting, in relation to fhe distributor, should be so arranged that the distributor brush is always ln contact with one of the distributor segments at exactly the same moment [hat the points of th ■ contact breaker begin to open. One hundred curves and hairpin heuds are in the IS miles of the Nurburg Ring, which has just been laid Put in the Eifel country. It is tho mrgest racing and testing motor track •n the world. The gradients range hom 12 to 27 in the 100 going upward, end the down gradients to 11 in the 100. There is hardly a level yard of it.