HINTS ON MAINTENANCE.
Page 26
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How to Get the Best Out of a Vehicle, to Secure Reliability and to Avoid Trouble.
626.—Preventing Movement Between the Rear Axle and Springs on the 2i-ton Dennis.
A trouble which sometimes occurs on the 2k-ton Dennis, apparently chiefly clue to neglect on the part of some users in the first instance, is slipping of the rear axle along its springs, thus tending to push the propeller shaft into the rear of the gear
box. The trouble can usually be traced to slight stretching of the four holding-down bolts combined with bending of the corners of the spring plate. Usually matters are left to themselves and the nuts not tightened until too late, with the result that the 1-in. nib on the bottom leaf of the spring wears out and there is then nothing to prevent the axle moving. As a result of not tightening the nuts periodically, these sometimes rust into position and it is then almost impossible to tighten them; it is often for this reason that the nibs are allowed to wear out. Even . when the bolts are kept tight it is sometimes found that the corners of the top plate bend.
The trouble can be overcome by making new bolts, in. longer, of good material, and also yokes, similar to those illustrated, of * in. thickness to fit across the top plates, thereby strengthening them. At the same time it should be ascertained that the nib on the bOttom leaf of each spring is sound.
627.— Some Notes on Valve Caps.
The removal of valve caps is often a matter of some difficulty. It can be facilitated by soaking the threads well with paraffin oil and rapping them,. on the tops with the flat face of a hammer, being careful not to make the blows too, severe in case the casting might be cracked.
It is sometimes advisable to run the engine for a few minutes before attempting to remove the caps.
Some of them appear to have far too many threads, half the usual length is often sufficient, and where the threads extend for a great length the lower half can be turned off in the lathe, leaving the bottom part of the cap as a kind of plug so B42
that the compression is not altered to anything more than an infinitesimal degree. Before refitting, the threads should be smeared with graphite, which prevents corrosion. Particularly is this necessary in the case of an engine the cylinder head of which becomes very hot. In one case of an inlet cap the top was broken off leaving nothing but the screwed portion, and as a spare was not available at the time this damaged end was faced off and a plain washer,• * in. thick, large enough externally to make a joint on the top of the cylinder and bored internally to pass over the threads of the sparking plug, was fitted over the cap body. The sparking plug was then inserted with the gasket above the washer and screwed tightly into the cap body, the whole then being replaced in the cylinder with the usual copper and asbestos washer between the steel washer and the cylinder.
If this had happened in the case of an exhaust valve cap it would simply have meant changing the cap over and utilizing the exhaust cap over the inlet valve.
628.—Repairing Tractor Wheels with Broken Spokes.
In steam tractors the spokes in the type of wheel which we illustrate sometimes work loose or break off close to the hub, but, in the case of an emergency, they can still be made good for hundreds of miles' use if, when they are first seen to be loose or broken, a steel casting resembling that shown in our sketch is obtained, made to fit tightly round the hub and secured to each spoke by or *.in. bolts.
Should the spokes be defective at the other side of the wheel, a casting will also be required there, and, of course, the repaired wheel will only be effective If the looseness or breakage is confined to a few of the spokes only.