MOTORING ......... NOTES

Manawatu Times, Volume 62, Issue 105, 5 May 1937, Page 12

MOTORING ......... NOTES

(BY “CAMSHAFT.”)

found that tho mixture can then be weakened, without causing flat spots or ! impairing pulling in top gear. Before drawing conclusions from the above tests, it is of course essential to make sure that where an adjustment is ' provided for altering the strength of j the slow-running mixture, the setting is ) correct. Most motorists, however, are j familiar with the symptoms of an over-1 rich idling mixture, which results in ' ‘‘hunting,” accompanied by black smoko from the exhaust. Plug Gap and Slow Running In this connection it is still a fairly common belief that a reduction in the 'sparking plug gap will improve the slow running. This belief probably originat--1 ed during the days of magneto ignition, ! when a magneto had to be in good condition in order to provide a long spark • when turning slowly. As tho magneto became older, the plug points had to be I closed in order to allow the spark to ’ jump the gap when idling. I Functional}-, of course, the longer the spark tho better combustion will be, for any loan spots or local aberations in the mixture will be bridged. The difficulty is to increase the plug gap without imposing an undue strain on the windings of the high tension circuit. To-day, however, designers, with the cooperation of ignition-equipment manufacturers, are experimenting with wider plug gaps, and it has been found that the increase in efficiency when a wider gap is used applies not only to idling conditions, but throughout tho whole speed range, and that the improved combustion allows considerably weaker mixtures to bo employed. At present designers are successfully employing gaps of 40-45 thousands, while it is hoped eventually to increase the gap to 60 thousands, or even more. Spark Intensity An increased voltage is, of course, required as the plug gap is increased, for the intensity of the spark is as important as its length. A surprisingly largo number of people believe that tho intensity of the spark has little effect on combustion, arguing that if a spark takes place regularly the mixture will bo fired, and that beyond this point tho spark cannot have any effect on efficiency. Most owners are now aware that tho popular method of testing a plug by laying it on tho cylinder head with tho lead attached, and turning tho engine by hand, is not a conclusive one. Tho ability of the spark to bridge the gap under atmospheric pressure is no guarantee of its ability to do so when subjected to a pressure of 1001 b per sq- in. or more. Even should the current not leak across the insulator, the intensity of the spark may not be sufficient to ensure complete combustion. Similarly, many owners place implicit faith in the conventional form of neon tester; but this is only a limited guide to sparking-plug efficiency. It is usually taken for granted that a flash in tho tester proves that the plug under test is in order. In practice, there is only one condition that wil lead to the flash not occurring, and that is when tho current is short-circuited directly to ; earth as occurs for instance when tho [points are short-circuited by carbon or moisture, or when the current leaks across the insulator. On the other hand, should the insulator be only partly conductive, so that the current sparks across it, or 'from the insulator to the interior surface of the plug, a flash will be obtained in the tester, although from the combustion point of view the plug will bo almost useless. So far it has been assumed that current actually reaches the plug. Many owners will probably bo disconcerted to find that if a plug lead is removed whilo the engine is running and the neon tester is held to tho free-end, a perfectly satisfactory flash will be obtained in the tester, although no spark is occurring. i It is posible for an expert to diagnose plug condition by studying the appearance of tho flash, for its intensity will vary under different conditions, and it is worth while experimenting with plugs that are known bo bo faulty in order that the intensity of the flash under different conditions may be judged. Question of Contact Another misconception which is widespread is the attempt often made to cure an elusive misfire by tightening each plug terminal carefully. If a lead is removed from a plug and held a short distance from tho terminal, the manner in which the spark jumps the intervening g a P will quickly demonstrate that a perfect gap, or even a contact at all, is unnecessary. In the vast majority of ignition systems, tho high-tension current has to jump au air gup in the distributor, from the tip of the rotor to each of tho segments. On the other hand, it is not always appreciated that the efficiency of tne low-tension side of the circuit is very quickly impaired by bad contacts; yet this side of the ignition system receives very little attention from the average owner. When the voltago is low, as is the case with the six or 12-volt system fitted to a ear, very good inetal-to-mctal contacts are essential to ensure maximum efficiency, and careful cleaning and tightening of the L.T. terminals on the coil and distributer body, which are impaired by oil and greasy road dust, will nearly always bo repaid by easier starting and better running. Farthing, too, must be effective, since it is in this manner that the current returns through the frame to the battery. Misfiring cau sometimes be cured by careful attention to the earthing of the distributer body, particularly when a hand ignition control is provided, as the distributer then pivots, and earth connection is made either through the central driven shaft and gearing, which, of course, runs in oil, or through tho various sliding or rotating surfaces and the control joints—a far from ideal state of affairs. A flexible connection should be taken from the distributer body—the bolt j which locks the split clamp is a con-

venient point—and a bolt on tne engine, i If the engine is flexibly mounted, it maybe advisable to take the wire directly to a point on the chassis frame. ‘ CLEANING THE UPHOLSTERY. I STAINS, AND HOW TO REMOVE THEM. i Car manufacturers are devoting groater attention to tho beauty of tho car and its appointments, and in selecting accessories and fabrics for upholstery, manufacturers have learned to appeal to desires for luxury and cleanliness. But to keep any motor-car fresh and new looking on the inside, it is necessary to give an occasional cleaning. The first thing to be remembered is that the sooner dirt, stains, or spots are removed the easier will be the task and tho less danger there is of harm to the upholstery. Try to decide the nature of the stain and the type of upholstery material on which it is found. Cenerally speaking, motor-car upholstery can be classified in tw r o groups; pile fabrics and flat fabrics. Mohair velvets are pile fabrics. Leather, Bedford cords, and broadcloths are flat fabrics. The textile industry has been making rapid strides in the development of new fabrics suitable for the hard use to which motor-car fabrics are subject. < Just recently a new pilo fabric has been introduced. This is a mohair velvet, and it water and dust proof. It has 1 unusually short pile, and is known as Velmoda. This new fabric is the modern development of the old type plushes, but the perfection of a special coated backing has made possible new features and new advantages not offered in the old plush materials. Ease of cleaning is one of the outstanding virtues of this new fabric. Tho special backing prevents dirt from penetrating tho fabric, and dust can bo rapidly removed by uso of a whisk broom or vacuum cleaner. Tho material i is washable, and stains and spots can bo removed without evidence of slcaning rings. Mohair Velvets Mohair velvets have a low pilo surface made up of thousands of tiny, up- 1 right fibres in every squaro inch of fabric. Mohair, recognised by thousands as the most durable and most easily cleaned of all textile fibres, is used for the pilo of mohair velvets. They are pliable; therefore it is easy to get at the spots and remove them once and for all without fear of their returning. Tho surface of Bedford cords and broadcloths is flat and spots on them are not broken up by fibres, as in the case of pile fabrics. Spots on flat fabric surfaces tend to spread along the surface and be absorbed. Because of this it is more difficult to clean these fabrics, and care should bo exercised. , Cleaning rings may be made when , removing stains from Bedford cords aud ’ broadcloths, because cleaning solvents have a tendency to spoil the finish of } these fabrics. When this occurs, the ( entire surface should be gone over with ( the solvent, so that the appearance becomes uniform. . There are several common causes of stains, aud if the following directions are followed closely, little trouble will be had in cleaning automobilo upEolstery. All cleaning materials mentioned are obtainable at a first-class chemist, j Lipstick.—Pour a little petrol or carbon tetrachloride on the stain and imi mediately press a blotter firmly on the spot. Repeat this procedure, using a clean section of blotting paper, until the , blotter no longer shows stain. } Paint.—Rub lightly with a clean cloth (saturated with turpentine. Repeat until I the stain is removed. After removing the stain in this manner, rub over the j • spot with methylated spirits. | Sweets.—Sweet stains other than sweets containing chocolate can be re- } moved with a cloth wet with hot water or sponged with petrol or trichJorethylene. Chocolate stains can be removed . by rubbing with a cloth soaked in luke- ' warm water. After the spot is dry it | should bo sponged with petrol or tri- ' ehlorethylene. Battery Adds.—Speed in removing these spots is essential. Pour enough household ammonia water directly on • the spot so that it will be well covered. J Permit the ammonia to remain on the i f spot about a minute so that it will i have ample time to neutralise tho acid, t Then rinse the spot with a clean cloth r thoroughly wet with cold water. • Blood.—Rub the stain with a clean i cloth wet with cold water. For each i rubbing use a clean portion of tho cloth, t If this fails, pour a little household - ammonia water on the stain and, after ■ standing a minute, sponge with a clean > wet cloth. Hot water or soap will only set the stain. J Grease and Oil.—First remove all s superfluous grease with a dull knife. ’ Then rub the stain with petrol (free S from tetraethyl lead). To prevent i greaso rings, start well on the outside of > the spot, and ruT> toward it with a i circular motion. Always use a clean i * portion of the cloth. It is sometimes 1 ' advisable to wet the spot with the sol- | vent and immediately press a white [ blotter over the spot, repeating the pro* l 'ccss, but each time it is repeated be > sure to use a clean section of the » blotter. Water Spots. —Sponge the entire section showing the stain with a clean i cloth dipped in cold water. Sponge the spot with a cloth wet with petrol. AIR LEAKS AND ENGINE ! BALANCE. i s To make an engine run at low speed i without “missing” is considered a good j test of balance. It cannot be done un- , less valves are properly ground in and j each has tho same amount of clearance I between the end of tho valve stem and 1 the head of the plunger or tappet, or, in the case of overhead, push-rod operat- ; ed valves, between the end of the pusht rod and tho end of the rocker lever. • The adjustments to obtain these con-

THE “TIMES” ROAD REPORTS A feature of these motoring notes is the report on the road test of a new car. These will appear every week and are intended to help would-ho motorists in the selection of a car that will suit their needs. Reprints of the tests may he had free of charge on application to the Motoring Editor, the “Times.” Box 92, Palmerston North. ditions have been dealt with at lengt* in previous issues of the Times. But even when these conditions have been obtained, there are faults which will mitigate against even running. However well an engine may be balanced, mechanically, by the makers, it may be put out of balance if all the cylinders do not receive the same amount and quality of mixture. Since tho explosive force of the ignited gas in the cylinder varies with any variation in the proportion of air and petrol, it is obvious that anything which cau affect this proportion must also affect the expansion pressure produced above the piston, and this affects the balance just as adversely us au actual lack of balance in tho reciprocating and rotating masses. A little experiment will show this at once. Slacken off two or three manifold studs, just enough to allow some air to be drawn in on the induction stroke, and the smooth running of the engine at low speed will be at once upset. It will show how a very slight mal-adjustincnt may upset smooth running. Amongst the points where unwanted air can enter the cylinders are at the joints of inlet manifolds and the connections from the carburetter to the ' manifold. In the case of a multipleport manifold it is essential that all the j washers should be of the same thick- ; ness. If one must be renewed, it is wie to renew them all, for a manifold with several ports cannot be bolted up with equal security unless all the washers are of the same thickness. Worn Valve Guides. . The most usual cause of unwanted air introduction is at the inlet valve guides. The valve stem wears tho guide due to the frictiou and to the Jack of lubrication: this objection is best overcome by the uso of an upper-cylinder lubricant .in tho petrol. j ' Valves aud their guides do not all jwear to tho same extent. If they did, no greut disturbance of balance would bo caused by air leakage, since the carburetter could easily be set to provide a slightly richer mixture—which would l later bo weakened. But, since the w ear does vary, the leak must be eliminated by fitting new, oversize inlet valves and having the valve guides reamered out to lit the new valves. It is no use replacing valves with worn stems by new valves in valve guides which are themselves worn. Thus, when replacement is necessary, all the valves and all guides should be replaced by new. Alternatively, tho guides should be reamered or ground out true, and valves with oversize stems accurately fitted into them, integral Guides. Some engines—notably some smaller American engines—are not fitted with separate valve guides. The valves fit in holes bored and reamered in the iron casting of the cylinder block. This ap- ! pears to be a cheap form of construction, but as a matter of fact, a steel valve stem wears remarkably well in a cast-iron guide. In such a case the steel valve stem wears more rapidly than the guide and often the latter is so little worn that a new valve alono will cure the trouble. Where the guide is slightly worn, a dead parallel reamer can be put through the hole (from the underside, because there is no room to manipulate the reamer from above) and will make it true again without removing very much metal. An oversize valve will complete the repair, provided that the valve seat is refaced concentric with the guide. In some cases a simpler remedy can be effected where a collar washer is fitted round the valve stem. This washer nips a felt washer between the end of the valve guide and a coned recess in the end of the guide. The pressure for nipping is provided by a small spring around the valve stem, resting at its bottom end on the washer which holds up the valve spring proper and pressing at its top end on tho under side of the combination felt and steel washer. This has the effect of making an air-tight joint. The felt should bo occasionally lubricated w r ith engine oil. The spring can be wound out of spring steel wire of the gauge of very thick cycle spokes.