MOTORING

Nelson Evening Mail, Volume LXI, 11 August 1928, Page 12

MOTORING

NOTES FOR THE OWNERDRIVER ELIMINATING BODY NOISES COMPLETE SILENCE SOUGHT It has- been proved that a motor cat* travels with less,noise than any other vehicle, yet designers are not satisfied, and are always,striving to provide complete silence. Early investigations proved that metal sheets set up vibration, and sound was reduced by stopping resonance. As the more obvious causes of noise were eliminated, the investigations became more complex. Straight panels, curved surfaces, padding, and various experiments have led to a general improvement. The noises which occur to upset the occupants of a closed car are often directly produced hv the chassis or bodywork. Others may be called secondary noises, in that they are set up by the sympathetic vibration of a part, such as a metal panel, which is excited- at certain speeds (varying according to its natural resonance.) by vibrations coming from part of the engine ,or the trains-, mission system. “Sympathetic .vibration” is. well known, a good example being a thin glass howl on a piano which will respond to the striking of a certain note but to no other.

' Another aspect of the subject is the use of the bodywork to insulate the occupants of the ear from'' the noises produced iit the mechanism. A simple experiment may be made by removing the carpet and floorboards at the front and driving the car without them. Most people who try this are surprised by the amount of noise coming up from the engine and gear-box. The degree of noise insulation produced by various substances is shown in a series of diagrams reproduced, which indicate the amount of noise transmitted through the substance, and the balance which is 'reflected. It will be seen that threeply wood and glass are excellent noise insulators, compared with a combination, qf cloth and fabric. Unfortunately, however, the very materials which are excellent as sound insulators are apt to set up noise by resonance, whereas cloth, while not a good insulator, cannot very well lie sot into vibration in this way. Some combination is therefore indicated, such as three-ply covered with fabric, with a layer of wood between the two. j

The degree of irritation caused by drumming also depends materially upon the effectiveness of the body in absorbing noise; the sound must be given means of escape or it will build up to a volume which is unbearable. Thus to open the windows of a saloon ear which is being driven at the speed at which drumming occurs would greatly relieve the trouble, whereas at other speeds it would allow external noises to enter the body more readily. It is not generally known that a human being has a considerable capacity for absorbing sound, roughly equivalent! to 5 square feet of window space, which means that the carrying of an additional passenger is as effective as opening a window with an area of five square feet. It follows that a drumming period is less troublesome when a ear is full of people than when it is carrying the driver oilly.. Other materials have been compared with the effect of an open window in the releasing or absorbing of sound by Major Tucker in his researches on the subject of noise in civil aircraft. He found, for example, that balsam wool has an effectiveness of 48 per cent, of “open window” area for area, making it particularly suitable as a lining for fabric bodywork. A carpet with a thick pile has an efficiency equivalent to .25 per cent, of its area in open window space, and so on. These figures have been determined experimentally for a sound frequency of 512, and average pitch. PROPER CARE OF TUBES

Ninety per cent, of the tube troubles are due to pinching from improper application of the tyres to the rim. Either a flap gets misplaced, a tyre tool gets jammed, against the tube, or the beads of the.ease, catch it at some place where it is creased. The result may be merely a pin-hole puncture,, or the pinch may be large enough to blow the casing off the rim. Practically all instances of a tube letting go inside the case, without outside evidences of injury, are due to this cause, or to a bruise break in the fabric pinching the tube. When a tube is put in a case it should be lightly inflated and the hand slipped around inside the case to feel that there are no wrinkles. The flap, if any, should be put in position in the same way. After the case is on, and before final inflation, the bead should be raised all round with a tyre tool to allow the tube to escape into place if the beads are pinching it anywhere. Sec that the valve stem is free by pushing it in and out. Attention to these particulars will prevent subsequent trouble. Many tyre experts agree that more than half of the number.of tyre are due ( directly or indirectly'to under.-inflation.- As- it is, in the case of the pneumatic tyre, not the lubber, but the air which carries, suspends, and cushions the weight of the vehicle, everything, of course, depends on having as much air as possible in the tyre tube, without approaching the breaking point of the rubber at the weakest point of the tube.. Every molecule of air which can he safely held in place in the tube helps to do tlie work for which the tyre is employed. Incidentally it keeps tube and casing in the most desirable form for which they arc designed, and holding them rigidly, offers stones, nails, and other soad sundries such resistance as is needed to make the impact harmless. OVER-COOLED ENGINES In the winter months it is by no means unusual to find an engine running at too low a temperature to develop full power and to run with the utmost economy in fuel. Troubles clue to overheating in hot weather have led manufacturers to provide more 'efficient fans and belt drives. As a result the air draught through the radiator will frequently not only prevent overheating in summer, but will cause overcooling in winter. Especially is that the case when an industrial vehicle is used for short runs on town journeys. The engine never has time to get warm, ami pulls sluggishly all day. In such cases it is often advantageous to remove the fan belt in cold weather to allow ih? cooling water to reach a. h’jsKef .Itompefatuic. ;thc ’best: temperature sip which tto>' run "air' internal ''combustion engine' has 'been shown to lie higher than that‘of tlie boiling point of water. Obviously, however, this temperature cannot bo attained with the usual cooling medium. The nearest safe approach to it is 10 nr la degrees below tlie boiling point of water; but even if tlie fan belt be removed on cold clays the temperature will rarely reach this point on short

runs, and in some eases it will not he exceeded oil long journeys, except in hilly country. FAIR PLAY FOR THE STARTER Where coil ignition is installed, the greatest caution must he exercised to avoid using the starter motor without first placing the ignition lever at the retarded position. .Neglect of caution may he responsible for very serious damage to the starter motor housing, and, what is worse, to the flywheel gejir. In the case of some ears, damage tojthe ilywheel gear is the more serious because the teeth are cut in the easting itsjelf, and a replacement is quite an item. When damage of this kind has occurred, the best course is to have the flywheel machined to take a detachable gear riiig. The price of a steel replace, meat (which is stronger than the gear of the existing flywheel), together with the. cost of machining, assembling, and fitting, is very much less than the price of a new flywheel, and though tin; ring is not obtainable from the manufacturers, it can be supplied by those who specialise in replacements for American cimssis. GEARBOX IMPROVEMENTS The gearbox has received a tremendous amount of Study during, the last .few,years with a view to reducing the noise emitted on ah indirect drive, and nowadays it is almost invariably the. practice to grind the gear teeth after hardening to correct the-effects of the distortion occasioned by heat treatment. Coupled with this, the mounting of the shafts has been improved, so that, although the ideal condition has by no means been reached, the gearbox is not nearly so bad an offender as formerly. Developments in this connection are represented by the use of internally cut gear rings in America, and constant-mesh, helical toothed wheels in England for the third-gear ratio' of a four-speed box in order to promote silent running. There has been a corresponding improvement in finaldrive gears, and bevels do not now, as a rule, become noisy until a considerable mileage has been covered. Latterly several important manufacturers have gone over to. the worm drive, and, while it is inopportune to enter into a technical discussion of its relative merits, it may he remarked that a, worm-and-wheel gear, if properly lubricated, never loses its initial silence of operation.

EXAMINE THE WIRING In many low-priced cars the tail lamp wire passes through a hole drilled in the mudguard or rear cross member, which, having sharp edges, will cut the insulation and short circuit the wire within a few months. As this exposes the owner to the risk of a fine the wiring should be examined, and if it passes through such a hole measures should be taken to protect the insulation. The best way is to get the local garage man to turn up on his lathe a small fibre brush to fit tightly irf the offending hole. Another good plan is to wind insulator tape round the Wire until it is a very tight fit in the hole, and as no movement is then possible there is little risk of the insulation being* damaged. A further safeguard is to pass a short length of rubber tubing over the wires.