MOTORING.

Gisborne Times, Volume LXXII, Issue 11452, 28 February 1931, Page 10

MOTORING.

HOW CARS CATCH FIRE. •v Dealing with lio subject of motor car fires the “Motor” remarks that the safest position for the tank is only one ground for inquiry ; another is its design and construction. In at least one case the tank is so built that it is practically invulnerable, while in others it is so lightly constructed and it is easily ripped and the contents spilt. ' ' , An important consideration is ease of exit in cases of lire. In some cars we have tried it has only been necessary to place the wheels on the kerb on one side of the road for body stresses to be set up which make it almost impossible to open the doors. Two'-doyr .saloons, not so popular as they were, have tlio disadvantage that the rear passengers cannot jump out until the front passengers have escaped. Narrow windows make it difficult to clamber out of a car that way, even if the glass can be readily broken, and this is naturally more difficult in the case oi the unsplinterable type. 1 It would he important, it it were possible to ascertain what is the direct cause of cars catching fire, but in no single case lias it been possible to do so. Exhaust pipes do not run hot-, although there is always the possibility of the exhaust from a fractured pipe igniting spilt petrol. So far as the electrical equipment is concerned, tho chief risk is that of short circuit of leads connecting with the battery. In a general smash-up it might occur at the switch-box connections. The fact that leads arc usually armored diminishes the risk to some extent, but with a charged battery there is bound to be some danger. Another possibility is that a spark from the dynamo brushes might fire the petrol, as tli e dynamo may continue to run a sufficient time after the accident. Possibly even a spark from tlio distributor might cause ignition. It is extremely difficult to seo what can be done to elucidate tlie causes of fires in tho case of overturned cars, the chances being that experiments would not reproduce tho conditions that occur in accidents, each one of them probably # being different. CLICKING NOISES, PHEN OMENON~WHEN CAR COOLING. When a car is parked immediately after a run on the. road clicking noises ai-e often produced. No harm is done by this action. • “Clicking” is usually duo to tlie cooling and contraction of tho exhaust manifold, exhaust piping or silencer. There is »- number of joints in ’the system, gripping by friction, and'when contraction of tho cooling metal occurs such a joint , will not at first give way; tho metal is thereby placed- under tension. . This tension increases: to a point sufficient to overcome tlie friction and then a sudden “give” takes place, producing clicking: Tho process repeats itself until finally tho system becomes cool. The flanges-with which an exhaust manifold is secured to the cylinder block constitute a good . example of this- proccts, particularly in the- case of a lengthy engine". Rib by hit cadi fla-ugc slips, grips and slips again until the manifold- is cool. Tlio total movement is, of course, very small and-is permitted by tlie clearance between . each holt and the hole through ,which it passes, INCREASED: ENGINE SPEED. ’ ONE OF WONDERS OF AGE. One of the most important develop-ments-in automobilo \ehgin© design of , recent years- has been the stepp-ing-up of , tb© ; revolutions a minute. Less* than 20 • years ago, -the fourcylinder power units, oven in racing i cars, ran-at about 2500 i\p.in.; today racing engine spe.eds of 5000 to 6000 r.p.m, ar© not uncommon, ancl even passenger,- cars • nowadays often touch between 3000 and 4000 -. revolutions. _• - Tho object of; lliis increase in ©hr , giuoV speed is to • obtain mof e - power 'displacement. ;V , ' ■ ■ : i' V - '

This increased spqd is obtained by better balance of reciprocating parts, larger valves, different cam setting and lighter pistons. The latter arc now usually made of aluminium alloys instead of the heavier cast-iron typo, an additional advantage being that the alloy piston conducts heat away from the piston head quicker than the heavier metal.'

That engineers have bqen able to design and produce power units of extremo lightnoss and high efficiency that will stand up to sus twined work for long periods without-engine fatigue is one of the wonders of the inotor-car-ago

ENGINE’S CONDITION

DEVICE FOR DIAGNOSING

As a doctor can tell the condition of the human body by means of a stethoscope, so can the -service, man ascertain the condition of an engine by tlio use of a device which has been, invented, This device is a well-made and compact unit having two dials. It has many applications and can be used lo indicate the condition of each. part of? the ignition equipment, to ■show the cylinder balance and the degree of vacuum .in each cylinder; it shows also whether a valve is leaking or sticking and whether tlio valvc-timjing is late. Air leaks are revealed, and weak valve springs arc indicated, in a quite simple manner. Thus, with this instrument, a service man is able to dagnose quickly any of these particular faults which frequently are hard to locate. The result is that there is no wastage of time and trouble, with a probable saving of expenditure for the car owner.

There are two dials on th e device, one on the left indicating the degree of vacuum which exists in each cylinder, while that on the right, in conjunction with a plug indicator above it, is used in testing tlio ignition system. The necessary connection's for linking to the ignition or the induction manifold arc provided, siiid it* is a very easy matter to use the device for any of the tests indicated.