MOTOR & CYCLE.

Taranaki Daily News, 1 November 1919, Page 9

MOTOR & CYCLE.

MAINTAINING EFMCIEIfCY. t it is strange how often one hears a motorist boast of the fact that his car has run for two or even ihres years ■without being overhauled or tuned up. Where this occurs, it is generally to be found that the owner is without that sensibility and sympathy which enables him to realise when his power plant begins to slowly tout surely fall oif in effectiveness* The change is slO'V and gradual, no doubt, but still it should he possible to locate it, and ic is of great importance that it should bp realised at once, for it inevitably denotes the need for attention. Tiia most serious source of loss, as a rule, is want of compression. This may arise from a variety of causes, such as the pitting of the valves, the fact that one or other of the valves fails to close absolutely, duo to the end of the tappet rod remaining in contact, the breakage or wear of piston rings, or the shifting of same, so that the slots come adjacent to each other; a bad joint in the cylinder head, allowing the escape of compression: or wear in the cam surfaces (which is rare). Sometimes the trouble may be only in one cylinder, making it more difficult to diagnose. If the trouble is serious one can test it by slowly turning the starting handle, but. as a rule, a compression gauge is necessary, and unless the owner has some exper', Knowledge it would'be better for him to take the car to an expert. Another fruitful source of trouble is the deposit of carbon on the tops of the pistons' anil the wn'ls of the combust ion chamber, due, osualiy, to excessive lubrication causing the cil to get past the piston rings, and in some cases to faulty earburation. Such deposits, needless to say, reduce the size of the combustion chamber, and also is likely to cause pre-ignition. The valve timing also may bo faulty, needing the re-setting of the tappets. The clearance should be only jußt sufficient to leave the smallest possible space between the top of the tappet and the valve stem; about l.C4th of an inch is ample. Ignition troubles, also, will cause a falling off in power. These may result from ordinary short circuits, or may be due to the ends of the plug electrodes being too far apart, or too close, or through the space in the respective cylinders varying. These snould be set absolutely to gauge, and. to ensure tlioir synchronisation, should be checked at regular intervals. Wear in the contact maker disc or contact points will also cause trouble, and sometimes the fibre disc is at fault, or the distributor is dirty or worn. An occasional overhaul of a car is wise, and a payable outlay in the long run. ? LIGHT MOTOR CYCLES. Those firms who confine their programmes to the manufacture of lightweight motor-cycles alone are, says an Knglish writer, experiencing an nnpre. ccdented demand for machines at the present titne, and if it were possible to compare the number of orders pmced for all classes of motor-cycles, it i= more than likely the lightweight would predominate. A factor in the situation is no doubt tile lower initial cost- 01 the medium powered, and especially the single-geared, machine, although tnis approximates to, and in many efcscs e> eeeds. that of the SV, li.p. standard of the pre-war period. Then again, purchasers loo!: to the cost of Tunning their machines when they ;rct them, and the lower petrol consumption, longrr life of tyres, and greater economy generally of the lightweights weigh in favnr of the latter to a considerable extent Mot that the more, powerful and higher, priced models are not, in demand, the nor.ition being in many factories that orders for delivery this year have ceased to be accented for the reason l hat in present circumstances it would be impossible to execute them before the end of 101!) The lightweight firms, including those who niarkc-.t. heavyweight machines as well, are equally stressed with work, and it is often the lightest and cheapest, machines that form the bulk of the trade. The popularity of the lightweight is already established and the conditions now prevailing appear likelv to accentuate rather than diminish this. THE SH.EXCER. It is rather remarkable tliat the silencer, of all parts of motor vehicle construction, seems to have received less consideration from the manufacturer and designer than other parts, which anparentlv appear to be of more importance. But there is no doubt that a great deal of car inefficiency is due to inefficient silencers. If a silencer impresses a considerable hack pressure on the outflowing gases, it has the effect, of interfering with the scavenging of the cylinders on the exhaust stroke. This will result in overheating, ns well as bnck pressure, and both will tenil to reduce the nower given off very considerably. Not only this, but inefficient scavenging is a direct cause of carbonising in the cylinder head and on the pistor.s. and for that reason alone it is advisable to get as large as possible an outlet for the exhaust gases. WEIGHT OF MOTOR CYCLE OUTFIT. When the first sidecar was clipped into position beside its 2 h.n. machine little did we. think that a few short years would see machines on the road tipping the beam at 4ewt. Yet this is the total weight of an outfit as quoted by a weighbridge. Needless to say, the machine was equipped with a roomy body, and ifs owner was one of the fraternity who insist upon bavins-"two of everything"' as far as practicable. It should lie interesting to any owner of a really business-like turnout to see it on the scales, and it is feared that the example just, referred to would have plenty of company in its own class. As a matter of fait, verv few riders realise the weight of their outfits until a kirk, starter packs up and a start has to be mnd»> on a hill, at which period anvhodv will believe any old weight, provided it 1 runs wll into tons! Tt. is sincerely to he hoped that the sidecar will e.ol cventunlly die. the ?ate of the ancient tricar through over-elaboration. TtuUie;' let it , revert to the single-cylinder combina- ■ tion of ten years ago, sans clutch ftnd 1 gears.