MOTORING WORLD

Manawatu Standard, Volume LVIII, Issue 52, 29 January 1938, Page 7

MOTORING WORLD

TRACING FUEL LEAKS. A good deal of petrol can be wasted by leaks at the various union nuts on the pipe lines which connect the pump and carburettor with the rear tank. These should be examined occasionally and tightened carefully if there are any signs of such leaks. Perhaps the best way of testing them is to feel around each union with the fingers while the engine is running and sucking the petrol through. Any seepage of fuel will be felt immediately. In tightening these unions, some care must be exercised not to exert too much pressure on the union nuts. As they are of brass, it is comparatively easy to split them. Always use a well-fitting spanner and under ho circumstances a pair of pliers, as these will almost immediately make the comparatively soft hexagonal nuts round. When ethyl petrol is used, the search for leaks is easier, as this fuel will leave behind it a red deposit from the chemical with which it is coloured. OVERHEAD VALVE ENGINES. Although overhead valves are regarded in some quarters, quite unjustly, as an obsolete feature of design, the fact remains that some of tlie most popular, as well as some of the more famous of the expensive makes, adhere to this type of valve arrangement. The common objection of the practical motorist to overhead valves is that they are apt to be a little noisy in action after some thousands of miles of service, but, while this may be due to an extent, it is very doubtful whether this noise is not more than offset by the increased efficiency which is generally obtained from this valve arrangement. Sometimes their noise can be practically eliminated by very careful adjustment of the valve rocker arm clearances at the head of the push rods, but the motorist who insists on having this work done must remember that overhead valves are much more sensitive to valve clearances than side valves. Even in the interests of silence, it is very unwise to adjust overhead valves too closely, because the long push rods operating them naturally expand more under the influence of heat than the shorter tappets of side valves., Consequently, overhead valves must never be adjusted to closer tolerances than those advised by the makers. If, when this has been done, the valves are still a little noisy, it is unfortunate, but by no means serious. In any event, noise from overhead valves, generally, is only heard when the engine is idling. At ordinary cruising speeds, it is not apparent at all.

MODIFYING SHOCK ABSORBERS

Motorists dissatisfied with the riding comfort of their cars on the grounds that far too much bounce is evident after passing over potholes and bumps, can often improve matters by having the shock absorbers adjusted to impose a more restraining influence on the springs. If the shock absorbers are of the type which cannot be adjusted, the experiment may be made of draining them of the original oil and having a heavier grade put in. This, by not passing through the vnives so freely, lias the same effect as closing the valve-apertures in the adjustable type.

REDUCTION OF WHEEL WEIGHT

Some very important changes have been made in wheel design in the last few years. For many years, American cars were fitted with hickory wheels having detachable rims, while British makers favoured the steel artillery type with the manufacturers pf expensive and sports models using the wire type, then the strongest type known. The revolution started with the gradual reduction of wheel diameter to make room for tyres of larger section, and it was aided by the gradual disappearance in America of the hickory forests from which came the wood employed. In America, the first step was to adopt the wire type, a very smart wheel, but an appalling thing to keep clean. English makers followed suit. An early, short-lived attempt to after wheel design was to adopt the disc wheels, but this acted as a diaphragm and so exaggerated chassis noises that it was dropped very quickly. After the wire wheel came the pressed steel artillery wheel, light, strong and good looking, and this lias been followed in the last two years by a revival of the disc wheels, but with perforations round its periphery to help stop drumming, a fault which in any case would not be so apparent in these later types, as they are practically only a hub with a very fat tyre attached. As the wheel as such is gradually disappearing, a writer in an English periodical puts forward a suggestion that the tyre should be attached directly to a rim formed on the brake drum. This would aid brake cooling, but, more important, reduce the weight of the wheel and brake gear. It is pointed out that-very light wheels, having practically no flywheel effect, are most important for quick getaway, while they also improve a car’s suspension.

INSTRUMENT LIGHTING. A fault with many cars is that the illumination of the driving instruments, even though it be of the indirect sort, is far too bright, and after some time tends to dazzle the driver and interfere with his view of the road. In one case, the lighting was so bad in this regard, that the driver found a reflection of the two brightly illuminated dials rising in front of him on the screen and was forced to the expedient of pasting paper oyer them, as there was no separate instrument light switch. It is essential, however, that the instruments should have some illumination, so that the oil gauge and ammeter can be seen, while the imminence of rlie speed limit makes a view of the speedometer essential. As it is now, however, many drivers switch the instruments off at night. The problem is solved in an excellent wav in some British cars, and the idea is so good that there seems no reason why it cannot he applied to other models Brieflv, the instrument light switch is a rheostat, by means of which the degree of illumination can be varied to' suit the man behind the wheel. A rheostat is not a, very expensive device (those commonly used in radio should be excellent for the purpose), and there would be little difficulty in introducing it in the instrument board lighting circuit. It _ s operated by turning a small knob.

GUIDE TO MIXTURE STRENGTH

A T ough and ready guide to the strength of the mixture provided the engine by the carburettor is the condition of the sparking plugs. If they are sootv, Rie mixture is too rich. If they are dried up, with traces of a flaky

white deposit, the mixture is too weak. Particular notice of the plugs for this purpose should only be taken if they all display more or less the same condition. It is possible that only the two cqntre ones will show traces of soot, the others beings normal. If this is so, an indication of the difficulty manufacturers face in getting an even distribution of the mixture to all cylinders, and the condition is caused by faulty induction pipe design. The motorist can do little about it.