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79. — Foden Safety Valves. After a Foden steam wagon has been

6th September 1921
Page 30
Page 31
Page 30, 6th September 1921 — 79. — Foden Safety Valves. After a Foden steam wagon has been
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in service some considerable time it will be found that the bridge holding the two valves down on their seats, under the influence of a stout spiral spring, enlarges the holes in the tops of the valves and interferes to a considerable extent with their sensitiveness. The trouble can be cured very easily by fitting a small sheet brass disc into each recess thus formed. The disc should be brazed into position and faced off with a smooth file. It is not intended by the makers that the head of each valve should be perfectly flat. Each should be countersunk slightly to take the ends of the bridge. The brass disc should, therefore, be fitted only if the recesses have been worn unduly large, and, after fitting, each disc should be countersunk slightly, care being exercised to make the countersink exactly central. The nut for adjusting the spring on the safety valve is rather awkwardly situated and cannot be turned without the use of a special spanner with the jaws almost at right angles to the shaft. The makers send out a special spanner with each vehicle, but this is often lost and drivers endeavour to tighten the nut with an ordinary spanner or one of the shifting variety. The correct type of spanner to employ is shown in the illustration.

80.—Spring Lubrication. The writer of hint No. 67 dealt very thoroughly with the important but badly neglected item of spring lubrication. An equally important matter is the kind of lubricant to use for springs. The most common are thin and thick grease, a mixture of grease and graphite, or oil and graphite, and sometimes gear Oil. In some cases, "any old stuff" is used. The ideal lubricant for spring leaves is Russian tallow, and it is used so seldom as to give the imB34 pression that its existence is unknown, though engineering practice its use is universal for presE ing machinery from corrosion.. It has a consistei which is far and away superior to that of ordin grease. The latter soon melts, and moisture remai which corrodes and eats into the leaves. Russian 1 low makes a film which adheres to the leaves. II not so readily affected as grease by heat, and cor quently lasts much longer, and is to that extent in satisfactory. Dismantling springs is hardly a job within the CE gory of running repairs, while it is very doubtfu springs can be properly greased on commercial ATE des by the 1150 of devices for forcing the leaves ap; Smearing the sides of the springs with grease to le out dirt is hardly a practice to be recommended. Some makers send qut their vehicles leaving • springs, bright instead of painted, using the gaii and this is really the best practice ; the same reasi which justify its use on Ativate cars applying Ns equal cogency to commercial vehicles.

81.—Flywheel Wobble on Steam Wagons Any tendency to wobble on the part of the wheel of a steam wagon should be looked upon vs grave suspicion and -discouraged as quickly as sible, as otherwise it may result in the breaking the crankshaft or in the flywheel and shaft part company. The wobble may be caused in Bev( ways ; the crankshaft may he bent or loose in bearings, or, if the crankshaft is a new one, taper may not be correct; a loose key will also so times cause the trouble. Whatever the reason, engine should not be run for long in this -condft: as, even if the wobble be slight, a considers amount of vibration will certainly be piesent, this causes rapid wear of the bearings as well being most uncomfortable, and being liable to ea a fracture of the crankshaft. If .the flywheel comes off, or its removal has b necessitated, it is quite possible, in most cases, rim home at a fair speed.; in fact, the loss naturally, far more apparent when the enginE running slowly.

82.—The Dennis Water Pump. In the engine of the Dennis lorry the water pi has, a fibre packing washer with an ingenious arrai moot to take tip wear consisting of a. compres1 spring fitted against the end of the spindle, as is fluted and a sliding fit in the driving shaft, spring keeps the flange pressed against the f washer and ensures a water-tight joint until washer has completely worn away, which occurs a about 5,000 miles' running. A hole is left in. the casing surrounding the pi shaft, by which any water which leaks from the pi can escape. sometimes a short piece of pipe is flu into this hole to lead the water away. Drivers usually instnietect never, in any circumstances, plug this hole or pipe, but sometimes they do the result that the water runs down the bearing the driving spindle and into the crankcase, where may cause a great deal of trouble. It is always ter to fit a new washer as soon as possible. To do s, take off the front of the pump and also the nut of the snindle which locks the vane to the latter. It • is, preferable to do this before disconnecting the pump from the engine, as, the spindle will then be held firmly and will not have to be put into a vice, where there is a liability of damaging it.


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