HIGH ROAD & BY-ROAD.

Waikato Times, Volume 108, Issue 18159, 25 October 1930, Page 23 (Supplement)

HIGH ROAD & BY-ROAD.

GAS IN FUEL LINE. LOSS OP ENGINE EFICIENCY. Motorists will be surprised to learn that it is computed that about one car in every five loses engine efficiency in some degree owing to petrol gas forming in the fuel line. The cause of this trouble is usually owing to the petrol leading running too close to the exhaust pipe, or the carburetter, or the vacuum tank is over-heated owing to high temperature under the bonnet; this has a tendency to boil petrol and the resulting gas fo.rms-into bubbles that interrupt the even flow of petrol. This causes engine to lose power, misfire, and even sometimes to stop entirely owing to fuel starvation. It will surprise many car owners to learn that at about 90 degrees atmospheric temperature, the heat under the bonnet may climb ass high as 230 degrees, whiist the temperature of the carburetter jet may reach 175 degrees. This “jet” figure, the Dunlop Company states, was ascertained during recent tests at the University of Michigan (TJ.S.A.), where a carburetter made of glass was tested for petrol bubbles, under varying degrees, of heat. In the tests it was found that the petrol bubbles, at hight engine speed, were sucked through jet with little effect on engine running, but once the revs, got down, the bubbles increased in size, and choked the small orifice of jet. When it is pointed out that the volume of petrol gas is approximately 185 times greater than an equal weight of liquor petrol, it will he realised how impossible It is fpr the very small hole through carburetter jet to pass sufficient gas-to enable engine to function properly. This explanation will probably elucidate for many motorists why their cars run so much better and smoother during cool weather, than when the thermometer figures register high. To cure the trouble cited is in some cases a difficult matter, but where it is found that the petrol lead runs close to exhaust pipe or near exhaust box, and gets unduly hot, this can be remedied by lagging exhaust pipe with asbestos cord, or by removing petrol pipe to the oposite side of chassis. A cure has been effected in some instances by fitting a larger petrol pipe, and covering vacuum tank with asbestos sheeting. A change of petrol will sometimes overcome the trouble, for the more volatile the fuel is, the readier it will form gas, under heated conditions in petrol lead. A heavier grade fuel may therefore improve matters, although it may silghtly affect starting of engine, but that trouble, does not often worry Australian motorists during the summer months.

VULCANISATION. MADE RUBBER TYRE POSSIBLE. Vulcanisation first made possible the manufacture of rubber tyres and on this account it is interesting to know just how this process was discovered. Charles Goodyear spent many years in experimenting with gum trying to discover a method of treating it so that it would not stiffen with cold and melt with heat. He was only partially successful, however, until 1839, when, while talking and demonstrating to some friends in the kitchen of his home, he dropped a piece of rubber mixed with sulphur on the stove. It charred like leather. This was the discovery of vulcanisation. A discovery which has enabled the production of innumerable rubber goods. IGNITION. A very interesting point is raised in regard to car ignition by a well-known English competition driver, who states that there is no objection to coil ignition for ordinary speeds, but for high reving engines his experience has not been what he calls, “altogether happy,” and offers a word of warning to those whose engines are. expected to turn over at 4.000 or 5,000 r.p.m. with this means of ignition. Unlike a magneto, the spark Intensity of which increases as the speed rises, a coil does just the reverse, for the reason that, while the former both produces and converts its own current, the latter is a converter only and is fed by a constant current from outside sources.

The electrical procedure of conversion is the same in both cases; a low tension contact breaker closes for a certain are of rotation, during which the current, whether internally produced or supplied from outside, passes round the primage windings and builds up the magnetic field. The spark which passes on the subsequent “•break” depends for its intensity upon the strength of this “field,” the building up of which is not instantaneous, but depends upon the period of the contact and voltage of the low tension current supply. In both cases the contact period varies, of course, inversely with the engine speed; the higher the revolutions per minute the less time for building. Tn the case of the magneto being a producer as well as a converter the voltage of the primary current rises with the speed and balances up the shorter "building” period by producing a heavier current, so that the spark strength is intensified up to a point and then maintained, but not so the coil; while its building period is ever shortening as the speed rises its current supply does not rise, and the spark intensity 'falls' off. Ordinarily the windings and the contact breaker design are calculated to produce the requisite spark intensity up to the highest speed that the engine will fittain, but whereas a slight disorder will mainly affect starting and slow running in a magneto, It may readily cause the spark to fall below the useful ignition point at -high speeds in the case of the coll. This often occurs, especially when engines are speeded up a few hundred or perhaps a thousand revolutions in competitions. The coil maker is not altogether to blame, his apparatus is generally quite equal to peak revs., for which the engine was originally intended, but it would be well, perhaps, if the owners were warned that coils have a rev. limit, which very few motorists know. When therefore a coil-fired engine accelerates with great vigour up to a certain speed, just disconnect one high I tension lead, make an air gap at the plug terminal and rev. up hard. It I may he found that, the spark becomes | almost non-existant after a certain j maximum speed. !