MOTORING

Gisborne Times, Volume LXXXI, Issue 12398, 10 November 1934, Page 11

MOTORING

■ KNOCKS AND PINKS. DIFFERENCE BETWEEN ONE AND THE OTHER . If your engine is knocking, can y ou tell whether it is really knocking, pinking, or detonating? (askn Captain dc Normanvillc in the “NewsOhronicle”). All these three are generally looked upon as being the same. But they are quite different. And, ias their importance differs considerably, it is as well that you should know “t’other from which,” and how to find out what nilf. your engine. And it is a comparatively simple matter. A genuine “knock” is a matter which should have your early attention if you do not wish to be stranded and incur extra, repair bills. There is a distinct difference in the sound effect of knock by comparison with pinking or detonation. But many motorists find it difficult to tell one from the other.

If you have an unpleasant sound from your engine of the knocking or pinking variety, you should immediately see that you stop it. If retarding the spark elimin >tes the noise entirely, it is only pinking—and not serious.

But if when you retard the spark you still have a dull and subdued “thud” emanating from the engine, it is time to fear the possibility of a genuine “knock.”-Such a knock will be due to a worn bearing, either the “big end” or the gudgeon pin bush—' the latter is sometimes called the “little end.”

To make sure, you must become your engineV* doctor! You know bow n. doctor sounds a patient’s chest with a stethoscope ? You, can sound your engine’s chest ;n just the same wav.

You want a piece of hard wood, about a, foot ° r two in length and about half-an-inch fn diameter. One of the old-type circular wood miles is excellent for the purpose. The feared “thumping” of your engine’s heart is cither in the big end or little end of the connecting rod. Put one end of the stethoscope on the outside of the front or rear hearing of the crank-shaft casing, as may be the easier.

With the engine running slowly, placo the lobe of your ear on the other end of the stethoscope, and press your ear against with sufficient pressure to close the ear to any sound other than that coming up the piece of wood. Y T ou will now find your “dull thud” takes on a more definite sound. Transfer the stethoscope to the outside of the cylinder walls taking each cylinder in turn. The cylinder whic-li i's at fault will give a pronounced louder knock in the stethoscope than the other cylinders.

If you heard a similarly loud knock on the crank-shaft end bearings as well you will know that it i:> r, big end that i s worn. If the sound is louder on the outside of the cylinder wall, it will be the little end which is at fault.

Either should he seen to before it gets worse, but instead of saying to your repairer, “Thore’is something wrong with the engine,” you can say. “I want you to take the bottom half down, and just tighten- up No. 3 big end.” It’s a much cheaper j°h when you give Instructions like that! Momentary pre-ignition pinking (or, as it is so: often erroneously called, “knocking”) does no real damage—so long av, it is only momentary. But if the spark is not quickly retarded you tend to produce worse ills. Pre-ignition generally comes in this way. As your engine gets carbonised you reduce the available compression area, this tending to cause automatic ignition, and particles of tho carbon stand,up pinwaclc-wise and become incandescent.

This incandescent spot may fire the charge before the “official spark” actually sparks. And that firing taken place too early on the upward travel of tho piston. If your engine i s clean, and still shows an inclination to pre-ignite, the sparking plug is tho probable cause. Cham go it for one of accepted make with -a thicker centra] electrode.

SPEED MOTORING FOR A PURPOSE.

OVER, 3000 MILES DONE IN , TWENTY-FOUR. HOURS.

Ah. Jenkins, veteran speed king, shattered 75 world, international, alkl A,A.A. speed records a.n his recent 24 hours mn on .the hot salt desert .of Lake Bonneville, Utah, tJ.g.A,, with an average speed .of, 127.2 miles an hour including all stopo, oyer a distance of more than 3000 miles.

In writing of his experience i;n this adventure Mr Jenkins states: “This ; endurance run was the severest tent • to which I have ever subjected amy motor, and especially tyres.- My ear-, ; weighing over 5000 lb,- 7 travelled 3, 000. niilcS, averaging a speed of 127.2 nliles nari' hofir—breaking ' 77 world, international' and American records- ' all without tyrd troii'blo of any kind. .Firestone tyros gave an almost unbcliovcahlo performance in this run, particularly when you realise that the temperatures were as high as 120 degrees and that the holes in tho course had l been filled with crusted rock, that was ais hard as flint and I had, knife-sharp edges. This is tho • toughest rffn, I Have.'over mado in my :23 years of breaking .speed records.