QUIETER CARS.

Press, Volume LXIII, Issue 18917, 4 February 1927, Page 5

QUIETER CARS.

CHARM OF SILENCE. DETAILS REQUIRING ATTENTION It is not ninny years ago (sa\s a writer in the J»y'.]n«?y "Daily Telegraph") that tlie parsing of a motorcir was reminiscent of a travelling : ironmonger's simp with Iho noise of , the exhaust thrown in. Since then vr.sl ; improvements have been made, in the. j matter of reducing both mechanical ; and exhaust noises, and now the tnodI ern tar is almost inaudible on both I counts. There are, however, minor tici tails which still need the skilled atI lention of designers. ! Mechanical noises, by which aro | meant sounds other than those emailj atiii- from the. exhaust of the engine, ; are always an irritant to persons tra- ! veiling in the car, or to others who ! liear them at close quarters. On a ; long journey noise becomes a promiu--1 cut factor in (he matter of comfort; tired nerves are just as much a cause if the feeling of weariness as continual physical effort. No less important is the question of wear: it is quite correct to say that "here there is noise there is wear. . Me.-hanieal sounds are generally ■ nti««-il liy impact, with rapid attrition "f the surfaces in contact. Noisy Valve Gear. Ono of the most prominent of engine noises is clatter coining tioni tho mlvcs and valvc-opcruting nicchatiisni. Although tho modern engine is a considerable advance upon its predecessors, much remains still to ho done in this connexion, and it is quite probable that tho wider adoption of positively operated valves would go a long way towards the reduction, if not the elimination, of valve noises.

In order to counteract the effects of heat and consequent expansion, tappet clearances are provided, and these are prolific causes of the rattle and clicking which are objected to in many instances. The modern car engine which has side-by-side valves, usually has cover plates for the valve springs and tappets, but the adoption of the principle of lubricating the parts hy means of direct connexion with the crankcase, thus admitting oil vapour, is not as widespread as it might be. The provision of a cushion of oil between the valve stem and tappet head as occurs in a valve compartment fed bv oil spray, considerably quietens the clatter. Overhead .valves used to be regarded as inherently more noisy than the side by side typo, but this aspersion cannot be upheld in the light of modern example.;. Here, again, covers are highly desirable, not onlv to damp out the sounds which arise, but to keep out the dust which is bound to enter through the radiator and from below, setting up rapid wear and consequent mechanical noise. The use of springs on the rocker spindles is advisable for the elimination of side-play, which gives rise to clatter, and pressure lubrication to the rocker bearings is preferable to "hit-and-miss" methods, by which are meant systems depending upon the owner's memory for their efficienev. They consist in many rases of small oil-cups, which are very likely to be overlooked.

The practice of relying upon the oil mist from the crankcase passing up tho push-rod passages does not seem to have much to recommend it, especially in the high-speed engines which are embodied more particularly in the majority of modern light cars. Engines Once All Noisy.

Either the upper end of the pushrod or the underside of the rocker arm must have a cup into which tho other part fits; for the sake of retaining the oil which acts as a cushion between the parts, the cup should bo placed on tho push-rod, as it is then mouth upwards and can retain lubricant, whereas when the rocker arm is cupped it is mouth downwards, and runs almost dry for the wbolo of its life.

Engines of, say, 12 or 14 years ago, were almost universally noisy as regards the timing gear, which whined particularly when the engine was running and the car was stationary, owing to the absoncc of other noises to drown the humming. Spiral gear-wheels and silent chains have, for tho most part, replaced the offending straight-tooth gearwheels which give rise to the noise in question. There are, however, minor details which deserve attention even in these days, such as removable covers in the front of the timing case, so that the owner may be able to test tho actual adjustment from time to timo. At present it is often necessary to remove the whole front of the timing case in order to see whether the chain is slack, which, of course, is not a task that is undertaken cheerfully. In some instances fabric wheels arc employed in the gear train to eliminate the resonance of metal wheels, and tho life of these "soft" wheels is infinitely longer than would bo imagined. Their use does not appear to be so general as it might be. End play in the camshaft is another cause of noise, particularly when gearwheels are employed. It is quite common to find that one of the camshaft bearings is flanged, and a collar on the camshaft abuts against it, and, as narrow surfaces are used, tho durability of this system is generally poor. It would seem that a hardened screw passing through the tapped, timing case, and abutting against the cud of the camshaft would bo a preferable method, as it would be adjustable and easily renewable. More Rigid Support. Gearwheels mounted on the ends of camshafts have, as a rule, only one bearing, which takes the vertical loads. This bearing is in the crankcase, and, consequently, the stresses imposed upon tho wheel tend to bead tho end of the camshaft, which projects from tho crankcase. The proVision of outrigger bearings in the timiug case, into which the end of the camshaft would fit, would provide a steadier mounting, and give better and more permanent meshing of the gearwheels, which, of course, tends to quieter running.

Auxiliaries—by which are meant magneto drives, fans, magnetos, dynamos, and cross-hhafts —are responsible for a large proportion of the sounds coming from art cngiue. Back-lash is the most ; common cause of trouble, and the remark!* which apply to gearboxes, dealt with in a later paragraph, may be takeu as holding good in tliip case. " Tans and Starters. , Fans arc very apt to cause rattles in cases where tho bearings are not adjustable. Positivo fan drives arc becoming more popular, and, provided they are weil designed, thev are to be encouraged. An efficient cooling svstcm which operates without the aid of a" fan, is. of curse, preferable. Dynamos themselves are not generally noisy, but lack of efficient maintenance on the part of an owner eome-

i,. in tho coniniutinufi sets up squeaks in "ie tator. This of course, is no fault o. the design. . ~<- ~,:„„ It mav I* said. «itli .iust.fi«.t'nn. that tl.c" clcc-tru- stnrtcr_i> one ; most imisv auxiliary lit Imp.. «' ' , in cases where silent chain-drive.-, .111.1 the like :irc employed. i^„ r i', T There is no doubt mat " pinion is an efficient piece of mci-lia-•Mii. hut the noise "hich it. sets up. particuh.rlv after a little wear. mi fc iit well Ke Vliminatcl. for sliia I <-• engines, the .lvnann.tnr or s-inzc-unit svstcm has advnntaso. It may l>o driven hv means of •■. silent, rhnni, and it is quiet when driving tiee.ipne, o r hcing drive,, l.v it. A sde-,Cam and frcr-whccl poarins f»r a starting motur are an alternatif" whirl, "as prnveil efficient in practice in several cases. A Great Offender. l.»ne of the noi.-i'-st features of every cap is its -earbox. In recent, years the grinding of £cars during manufacture has ctiected a great improvement bv giving smooth-surfaced gear teeth, instead of ones which are minutely corrugated, and (ho principle of mounting gear-wheels on splincd shafts, so that tho wheels take their hearing upon the shaft, rather than on the tops of the (.plincs has resulted in reduced noise. The tendency to reduce the overall dimensions of gearboxes has given rise to narrow-faced gear-wheels, small bearings and narrow gear-wheel hubs, which "may involve a tipping of the wheels on'their shafts, thus upsetting tho pro|>or meshing and giving rise to whining. The modem gearshift is of much stouter section than that employed in o'cler vehicles, hut tho absenco of support in the centre is a lamentable feature. Take, for instance, a four-speed gearbox; there is a heavy load upon the second and third speed gear-wheels, which are mounted approximately midway between the two end-bearinps. Hie first and fourth snoeds have the benefit of support by arTjacent bearings,_ hut. the whole strain has'to ho transmitted through the shaft to the bearings, when running in second or third speeds. Casings which Distort. Aluminium, which is the material of which most gearbox casings are made, is not really the most suitable for its purpose from the sound-deadening point of view, but is commonly used because of its light weight and ease of machining. Aluminium is a material which does not possess great strength, and it is quite easy to distort a gearbox casing, which means that tho mesh of tho wheels is upset, and noise is caused. Cast-iron, although somewhat heavier, would be less flexible, and give an improved mounting for all gearshafts and wheels.

The substitution of fabric disc joints for the metal typo of universal in transmission systems has silenced much of the clatter which used to accompany old-fashioned cars. Two points which seem to escape attention in certain cases are the desirability of rigid propeller shafts and correct balancing, as, even with fabric joints, the vibration set up due to defective bnlance seriously stresses the bearings of the gearbox and rear axle, imposing additional wear and consequent noise.

Spiral bevels have now taken the place of the old straight-tooth type in rear axle, and have cut out the "singing" which used to be so common. The worm-driven axle, of course, is well known for its silent properties. Adequate thrust bearings are not always provided, and it is generally this defect which gives rise to noise from the back axle when cornering, duo to tho endwise forces upsetting tho correct meshing of the bevel wheels. The use of steel dine wheels is apt to intensify any noise which may exist in tho rear :mc.

A matter of importance in connexion with the castings for crankcases, gearboxes, rear axles, and so forth, is the necessity for avoiding large, flat surfaces, which net as sounding boards. For simplicity of casting, the avoidance of "nooks and crannies" is keenly watched, but the tendecy to increased noise is often overlooked. Sounds Which Travel. Those who have had the opportunity of using sound-detecting instruments have frequently been struck by the transference of sound which occurs in wings, body panels, valances, and so forth. It is quito common to be able to trace a small knock in an engine, for instance, being broadcast into space by means of wings and large flat surfaces about the car. The presence of rubber insulators behind the wing stays counteracts this tendency. Rigidity of mounting is essential for all parts, such as wings, undershields, and panels. If one portion only of a wing, for instance, be in firm contact with th© chassis, the rest of the part will "dither' and give off sounds in a similar manner to a diaphragm of an electric horn. The body of a car is apt to squeak if its various wooden members be distorted or caused to move relative to one another. Insufficient attention is often paid to tho desirability of having flexibly mounted bodies,-so that chassis distortion will affect the body to as small a degree rs possible. Particularly in tho case of saloon cars is the absence of humming or rattling desirable, as the windows and roof all tend to retain tho sounds, and, in many cases, magnify them. A small point, but ono worthy of observation, is the method of arranging the final discharge of exhaust gases. If the silencer tail pipe finishes in front of the rear axle it often directs tho flow of gas against the axle or brake rods. This would not seem to be at ai! a matter of importance, but tho variation of exhaust noto one to the movement of the axlo across the gas path is most noticeable in certain cases, and jars on tho nerves on long runs.

It should he remembered that a new car is almost invariably silent; tho true test of noiseless running is made when the car is past first youth. Good design and good materials in combination give durability and longlived silence.

An engine that is permitted to Jose compression is disagreeable- to the good driver and creates a larger running expense, causing loss of fuel and power. It is_ advisable to check up on compression in each cylinder at regular intervals upon all priming cups or remove all spark P'ugs, one at a time, and revolve crank. If tli » cylinder which has its priming cup closed or nlng inserted, resists to a good extent the efforts to revolve the engine, that cylinder has good compression. All cylinders can be tested in the same manner, closing priming cups and replacing spark plugs i" each cylinder when the test is completed. There are ether methods for testing, such as listening for hissing noises on compression strokes of pistons, a Mowing the car to go down hill with ignition turned off and with transmission in low or second speed to note the resistance of the movement of the ear which each cyeliuder offers, or a compression gauge may be used. L'sc a wet sponge or soft cloth when cleaning a dusty windshield, to remove (he dust, as the grit will scratch the surf-ire if it is wiped with a dry c.o.a. All tools neciib-uy for emergency Tork thonld be earned ifl a ear.