For DRIVERS MECHANICS, & FOREMEN.
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TEN SHILLINGS is _paid to the sender of any letter Which, we vublish on this page, and an EXTRA _FIVE SHILLINGS to the sender of the one which we selectas being the best each week. Ali notes are edited before being published. Mention your .employer's name, in confidence, as evidence of good faith, Address, D., M. and F., "The Commercial Motor." 7-15, Roseberv Avenue, London, _E.G. .1,
On Saturday, March `26th, light your lamps at 6.50 in London, 7.0 in Edinburgh, 6.54 in Newcastle, 7.1 in Liverpool, 6.57 in Birmingham, 7.0 ,in Bristol, and 7.44 in Dublin.
Repairing a Timing Case Cover.
The sender of the following communication has been . awarded the extra payment of 5,s. this week.
 "A.L." (Notting Hill) writes :--" It is extraordinary the number of uses to which ordinary gas and steam pipe fittings can be put. They are extremely useful sometimes where an emergency repair is necessary, and have the advantage that they can be bought at any time at the local ironmonger's. The sizes advance up to 1 in. in eighths of an incht, and in those sizes the threads are of varying pitch. From 1/ ins. to 3 ins, the sizes advance by eighths of an inch, and from 3 ins. to 4 ins, by a quarter of an inch at a• time, but in all sizes a.bove 1 in., the pitch of the thread is one-eleventh of an inch. This is important, and should be ,borne in mind by all mechanics. . The following describes one occasion when gas fittings came in very useful. "A lorry had met with an accident which resulted ie the starting handle bracket, which was in one with the timing case cover, breaking off, close to the latter. At first sight it looked like a job for the welders. On running my. rule over it, however, I found that the dimensions were such that, by .trimining up the outside of the sleeve, I could screw it near the Junetion with the timing case, so as to accommodate a 24 in. gas flange. Moreover, the thread of the Tatter was sufficient to overlap the breakage and served to hold the broken pieces together. To make the assurance doubly sure, however, I procured another flange and put that on the inside of the cover, after -having trimmed it down a bit in thickness so as to leave plenty of clearance for the gearwheels. I also took eff the threaded part. This repair was carried out some five weeks ago,, and, as I have not heard about it since, I anticipate that it is still doing well."
Some Ignition Problems.
 "C.T." (Penzance) writes;—" The most frequent cause of trouble in a high-tension magneto system is in connection with the sparking plugs. it can easily be traced to one or other ef the following causes :--0) Insulator cracked or, if of porcelain, broken ; (2) points set either too widely apart or too close together ; (3) plugs dirty, insulator being fouled by carbonized oil or soot. To remedy these failings (1) fit a new plug; (2) adjust the sparking plug points by means of a gauge, which can be procured from any accessory merchant, to .016 in. or, if the engine is oily, .02 in. ; improper spacing of the plug points is often the cause of difficult sparking; (3) the insulator should be scraped and the plug cleaned. " Troubles with the modern magneto are rare. They are usually indicated either by the engine misfiring at low speeds, or by its refusing to start at all. There are three causes of trouble, which should be immediately investigated :--(I) The contact .breaker may be dirty ; (2) the gap between the points maybe too small ; (3.) the arm may' be sticking. In this case the engine may probably falter, stop, and refuse to restart. The remedies are :—(1) Clean the contact breaker, using a few drops of petrol ; (2) adjust the gap by moans of the gauge, which is usually provided as part of the magneto spanner ; it should measure not less than .012 in. and not more than .016 in.; after any adjustment \ef this gap the greatest care should be taken to ensure that the locknut is properly tightened up ; (3) the fibre bush should be eased and the pivot cleaned until it works freely.
" If the trouble does not lie in sny of these three directions, take off the distributor cover and examine it for the presence of oil, carbon, or other foreign matter. This is sometimes found lying on the surface between the brass segments of the cover. Clean the 'distributor thoroughly with a few drops of petrol on a piece of cloth which is free from lint. While the distributor is open, examine the brush to see that it is quite free in its holder., and -that it is clean. Take great 'care when replacing the cover that the brush is not broken. If, after all this, the magneto still fails to give a spark, take off the dust cover and examine the collector holder and brushes. Be sure that the latter are quite free in. the sockets and clean. Inspect collector ring and give it the same treatment, as advised in the ease of the distributor.
"Over-oiling is a fregeent cause of magneto trouble. A drop or two every thousand miles is quite sufficient, -and, although in most magnetos a drain hole is made in the base, any excess of oil will find its way to some spot where it will cause trouble.
" Therei is one other .possible source of trouble lying between magneto and the sparking plugs. I refer to the high-tension leads. These may be the cause of short circuits if the insulation has been chafed through or if it has parished. To test this, disconnect the suspected lead from the plug and hold the end of it about one-fortieth of an inch from the plug or cylinders, then either run the engine on three cylinders or arrange fer someone to turn the starting handle sharply. If no spark occurs at the end .et the lead, the trouble may generally be traced to the insulation. Finally, if after all this there is still no spark, then clearly the magneto itself is at fault, and it is advisable to send it to an efficient firm of magneto repairers or to the makers; preferably to the latter, as they are most likely to do justice to a; machine of their own manufacture."