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HINTS ON MAINTENANCE.

23rd November 1926
Page 68
Page 68, 23rd November 1926 — HINTS ON MAINTENANCE.
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Which of the following most accurately describes the problem?

Recutting Stripped Axle Threads. Renovating a Thornycroft Camshaft. Curing a Fierce Clutch on a 15-ter Fiat. Obviating Boiler Trouble.

Renovating an Axle Casing.

TN certain makes of vehicle failure of the rear axle through stripping of the threads which hold the wheel-retaining nuts is a fairly common occurrence, not always due to the design of the axle so much RS to negligent maintenance, as, if rear wheels be allowed to become too slack so that the side play is excessive, they exert a hammering action on the nuts, which are quickly punched off the threads.

In one particular axle, which we illustrate, it was decided to recut the thread at the point (A). The thread diameter was 31. ins, and the size of the thread 10 per inch. Recutting reduced the diameter to ins., and a new nut to correspond was made from a solid piece of good quality steel, the threads being cut so that the nut was a tight fit on the axle. As a second precaution a steel bush was provided as shown at D. This was fitted into a thread cut in the inside of the axle tube, the threads, in this case, being 12 to the inch. This bush formed a locking collar for the larger nut, and to allow room for it the axle had to be shortened by 5-32 in. The driving shaft, of course, passes through the axle and through the bush nut, which was bored 2 1-32 ins, to allow the 2-in, shaft to pass. The original axle nut is shown at C.

No doubt users of this make of axle will recognize it from the dimensions given, although, of course, the principle employed in the repair can be applied to many types of axle.

Repairing a Thornycroft Camshaft. SOME time ago the owner of a Thornycroft found thot the end of the camshaft was so worn that it would not drive the pump, so that no oil was going through the bearings.

As the vehicle was performing an urgent task, and It was essential not to take it off the road for too long, the nut which holds the timing wheel on the camshaft was removed and a fresh nut made with a shank extending in. A i-in. hole was bored in the centre of this shank and was slotted to take the pump spindle. The nut was then fitted and fastened with a grub screw, which was also used for the ordinary nut.

This repair has proved so satisfactory that the vehicle has run over 20,000 miles without further signs of wear, and the expense of a new camshaft has been saved.

The Contraction and Expansion of Boilers.

IT is inequalities of temperature that cause most boiler troubles, and it has been demonstrated that these variations not only cause leaks, but also damage and the destruction of certain parts.

A plain jaiece of iron or steel can be heated within limits almost any number of times without decreasing c46 its strength, but a boiler is made up of many pieces of 'metal riveted together, and if one particular part be heated or cooled before another severe stresses are put on seams and plates ; in fact, the stresses caused by steam pressure are small in comparison with those caused by such unequal heating or cooling.

If, When boilers are on the road, they be maintained at a uniform temperature, top and bottom, and if, when cooled, this cooling takes place uniformly, boiler troubles will be materially decreased, and drivers can do 'much to help in obtaining a long boiler life by keeping the working temperature as uniform as possible.

Improving a War-time Fiat.

ONE of our readers has a 15-ter Fiat under his care, and for some time he experienced considerable trouble with the clutch. This is of the multiple-disc type. The trouble was that when the clutch was cold and the oil thick only partial disengagement occurred, causing grinding of the gears.

The difficulty was overcome by leaving out exactly half the total number of clutch plates and making up the space caused by their absence by turning up two phosphor-bronze rings to the exact thickness of the plates left out.

The phosphor-bronze end-ring which fits over the drum to keep the plates in position was left in its old place, and one of the new rings fitted against it. nalf of the clutch plates were then inserted in their respective ordsr. Then the second bronze ring, and, following this, the remaining plates. The reason for placing the ring in the centre is that the plates are then not all at one end of the drum, and so there is less friction when the clutch is pushed out.

The scheme has stood the test of 18 months' work. The clutch has never slipped and gear changing is greatly facilitated, whilst the bottom gear can be engaged with just a snick of the gear lever when the car is statioeary. The vehicle is engaged in timber carrying and it takes a good, heavy load every time it is out. In ascertaining the correct size for the bronze rings a calliper rule or Columbus gauge can be employed, taking care to press the plates together when measuring. Half the measurement obtained will give the thickness of each ring. Their internal diameter must be such as will give a good sliding fit over the drum for the larger plates, whilst the outside diameter of the rings should be the same as that of these plates.

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