AT THE HEART OF THE ROAD TRANSPORT INDUSTRY.

Call our Sales Team on 0208 912 2120

USEFUL IDEAS ON IGNITION.

18th November 1924
Page 31
Page 31, 18th November 1924 — USEFUL IDEAS ON IGNITION.
Close
Noticed an error?
If you've noticed an error in this article please click here to report it so we can fix it.

Which of the following most accurately describes the problem?

Informative Contributions from Two of Our Driver and Mechanic Readers.

AN interesting letter, containing full instructions for reversing the direction of rotation of a magneto, has reached ass from "R.D.F." of Newton-le-Willows, who secures the 15s, prize thie week, In order to simplify his argument, he assumes, in the first place, that the magneto with which he has to deal is designed to run in a clockwise direction, and that it is desired to fit it to an engiue with timing wheels set to drive the magneto in an anti-cleckwise direc tion. Fur the complete conversion of the magneto three alteration.; have to. be made. A new left-hand, or anticlpckwise, contact breaker must be fitted, the distributor gearwheel most be re. timed in relation to the armature gearwheel, and, in most modern magnetos, the pole pieces must be reversed.

As regards the first item, the expense of purchasing a new contact breaker may be avoided, and the old one used again.

The disadvantage of this course, a small one, is that the fibre heel on the rocker arm will strike the cam, when breaking the contact, instead of wiping into it, as it should. In the opinion of " R.D.F." this is of no great consequence.

He deals neat with the third item, describing haw the necessity for reversing the pole pieces may be determined. Ascertain in the first place if the pole shoes are of the extended ty-pe. To do this remove the end cover, the hightension slip ring and brush at the driving end of the magneto. Then take out the two screws which secure the

brush holder, and also the armature cover plate. The pole shoes will now be exposed to view, and will appear either as shown in the first of the accompanying sketches, or as depicted in the other two. These sketches show what is meant by the term extended pole shoes; these are used in order to ensure a spark of maximum intensity in all positions of advance and retard.

If the shoes be of the extended type it will be necessary to reverse them, and this will entail the complete dismantling of the magneto. Commence this operation by removing the end plates which house the ball bearings for the armature spindle. This exposes the pole shoes, mounted on a brass plate. The next operation is to remove the magnets. but before doing so be careful to place a keeper on them.

If the end plates of the magneto he interchangeable, the armature may now be withdrawn sad replaced in the opposite direction, thus obviating the need for removing the pole pieces from the base plate. If the end plates are not interchangeable, then the pole pieces will have to be removed and reversed.

The retiming of the distributor gear may be done as the magneto is being put together again, and in the folloWing manner :—On nearly all magnetos the distributor wheel is marked with two centre-punch dots, above which are the letters " R ' and " which stand for right-hand rotation and left-hand rotation. The particular magneto we are considering es clockwise, or righthand, and in order to effect the change to anti-clockwise, which is left-hand, the distributor gearwheel must be set so that the tooth apposite the letter "L" is opposite the centre-punch mark which will be found on the armature gearwheel.

Before replacing the magnet it is neeeesary, presuming that the old contact breaker is being used again, to reset this contact breaker and to cut a new keyway for it. To determine the proper position for the keyway, set the contact breaker in its full retarded position, and with the contact points past separating In the case of an extended armature type of magneto, the armature must be set so that the trailing edge of its cheek has left the extended edge of the pole shoe, and is 2 nom. or 3 mm. away from it. The key-way may then be marked and subsequently cut. If the pole shoes be not of the extended type, then the contact breaker should be set in the fully advanced position, with the

points just separating. Then fix the armature so that the gap between its cheek and the edge of the pole pieces is 2 mm. or 3 mm., and mark the keyway.

SPARKING plugs. can only be pro

perly tested if placed under pressure at least as great as that to which they are normally subjected. " F.C.S.," of Tremble, has seat the accompanying excellent sketches of an apparatus

which he has made to enable this to be done by any mechanic. The barrel of this apparatus is turned from a piece of 2-in. steel bar, the blank end being tapped to take a sparking plug as shown.

The ripen end is then screwed 11 threads per inch to accommodate the nut which secures the windoei in place. The latter

is a piece of glass in. thick. It is gripped between two fibre washers and held by a nut, turned to the shape shown from a 1,i-in. standard Whitworth.

The pressure within the tester is provided by an ordinary tyre pump connected up by means of the valve shown, aihich is screwed and sweated into the barrel. Provision is made for the fitting of a gauge which should be capable of registering a working pressure of 160 lb.

The outfit may be convenieetly arranged to screw down an to the workbench, and this can be done if it be equipped with a couple of clips of in. by 7'4 in. steel strip sweated round the barrel.

In operation the apparatus is quite simple. The doubtfid plug is screwed tightly into the end of the barrel, and a h.t. lead connected to its terminal. Air is than pumped in, up to a pressure of about 120 lb. per square in,, and current is then taken to the plug, either from a hand-starting magneto or an accumulator and coil, with a handoperated make-and-break.

Tags


comments powered by Disqus