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ROAD AND WORKSHOP by HANDYMAN

13th August 1965, Page 54
13th August 1965
Page 54
Page 54, 13th August 1965 — ROAD AND WORKSHOP by HANDYMAN
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Which of the following most accurately describes the problem?

Taper Fits—Steering Ball Pins

DECENTLY I was shown a steering

lever removed from a tractive unit where the ball pin had been found loose in the lever eye, being retained only by the nut. The eye of the lever was split. and this had released the tapered section of the pin from the grip of the tapered eye. The ball pin had been dancing for several miles with the split pin loose and ready to slip out or shear; the nut was also free on the thread. In actual fact, a few more miles would have meant the steered wheels would have gone their separate ways, with the fair certainty of an accident or ditching.

The driver had, in fact, reported something wrong with his steering—although not of a constant nature. There were periods of normal steering for several miles on smooth road, then a bump made the machine at once difficult to control. This meant no more than the ball pin dropping down and taking up the slack, and vice versa.

The main point of concern, however, was not so much that a steering lever was to be replaced, but how this lever managed to split. In the normal way, the matched taper of ball pin and lever eye can be mated together and tightened almost to the limit of the thread capacity. such is the tensile strength of the lever material.

Therefore, it would need a fault or flaw in the lever material to produce a

fracture. Careful examination found no trace of fatigue or flaw, but it did bring to light at once that the metal around the eye had been subjected to some very considerable hammering during its lifetime and was clearly bruised.

There was no mystery here. It meant that the ball pin had been removed on one or more occasions, and the eye had been hammered as a means of releasing the nip on the ball pin taper. This is a common enough habit, and can be seen in many workshops, yet it is not good engineering practice to hammer at the actual eye metal, which is already stressed because of the wedging force exerted by the taper pin. It is fairly certain that the eye failure was brought about by the hammer blows, which distorted material already under stress, and narrowed the safety margin below the point at which it could survive road knocks.

Whilst it is well known that many such ball joints need rather savage treatment

to loosen their grip, and many of them are difficult to get at (other than in the region of the eye) it should be remembered that striking the eye is a dangerous practice. There are extractors, of course. but in the main a shock is still required at the end of the ball pin thread: again. this can damage the thread section.

This is where science scores over strength, and to relax the grip or tension set up between two taper fits such as steering ball pins, all that is needed is a vibration wave in the region of the tension.

Therefore, if two hammer blows can arrive simultaneously on the lever or arm just clear of the eye and on the solid bar, the wave set up will loosen the grip. This requires space and a little practice, but never fails if correctly applied. Alternatively, where space will not permit double hammering, a solid anvil and a suitable heavy drift will produce a satisfactory result.

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