HINTS ON MAINTENANCE.
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How to Get the Best Out of a Vehicle, to Secure Reliability and to Avoid Trouble.
CONTRIBUTIOXS are invited for this page from mechanics, works staff and draughtsmen, and fleet managers,. drivers, garage foremen, and will be paid for on a generous scale. Every system, make, and type of commercial motor vehicle will be dealt with, and the matter should be written with a view to the disclosure of workshop and swage practice in the maintenance of a vehicle—practices which, whilst they may be quite normal, are peculiar to the particular vehicle and may not be generally known to those responsible for its running. Expedients and suggestions for overcoming roadside and other troubles are covered in the following page, headed " Roadside and Garage." Communications should be addressed to "The Editor, The Commercial Motor, 7-15, Rosebery Avenue, London, E.C. I."
149.—Cleaning the Oil Circulating Pump on the Dennis Engine.
This hint applies to all Dennis engines produced since 1914, except these of the 1 ton and 80 cwt. chassis. Negligence in giving attention to the sump strainer may occattionally result in carbon from the inside of the piston accumulating and bursting the gauze. This carbon may ultimately 'collect and build up round the oil pump intake, with the result that the circulation will 'become choked. Therefore, during an overhaul the pumn should be removed and thoroughly cleaned. It can be detached by remov• ing the five flange nuts and an additional nut on the pump base by the side of the brass hexagon plugs. Carefully note, when replacing the pump, that its coupling on the end of the driving shaft engages accurately with its corresponding register If the pump is held up into position by hand, and the engine gently turned, the coupling will fall into position quite easily. It should never be forced, neither should the nuts be started to draw it into pcsition, as this procedure is not only liable to bend the driving spindle, but it can also shear. the pin which secures the driving coupling and force the latter out of position. When detaching the pump, do, not prise it away from the case,, or the resulting burrs will prevent a satisfactory oil-tight joint. A. tap with a hammer handle is quite sufficient to loosen it, and when replacing the pump in position a paper packing can be used if found necessary.
150.—Lubricating System on Bristol Engine.
One of the features of the Bristol chassis is the extremely simple and efficient oiling system, which is most satisfactory from a maintenance standpoint, as there are no pipes or .unions to break, no pressure or release valves or gauges to give trouble, and only two simple precautions to take—one being to see that tlie. oil strainer in the filling orifice is kept clean; the other to make certain that the 'oil level is up to a position somewhere between the level fingers situated in the centre of the strainer. • The oil-circulating pump, which is 'carried in the sump, needs no attention other than an occasional inspection. The pump can be retabved without disturbing any other part by unscrewing two nuts which hold the cover plate to the under part of the sump. With this cover plate removed, the pump may be inspected or withdrawn bodily from its housing. From this point also the whole of the oil system may be drained.
151.—Maintaining Slide Valve and Piston Efficiency on Steam Wagons or Tractors.
Serious inefficiency, in working may be caused by steam leakage past the pistons and slide valves. In view of this fault, these parts should frequently be tested and, if necessary, put in order. In the case of a single-cylinder traction engine this is a simple task. Put the engine on its inner dead centre and open the rear drain cook in the cylinder. Open the throttle slightly, and if steam issues from the open cylinder cock, the piston is leaking, and probably requires new piston rings. If the leakage is slight, it may be possible to stretch the old rings sufficiently to repair them by placing each squarely on a firm surface and tapping gently with a light hammer on the inner.circumference. In a bad case the cylinder may have become oval, and require reboring, in which. case an oversize pistonn and rings will be needed. In order to test the slide valve, put the reversing lever on the centre notch, thus closing the steam ports Open the throttle slightly, and if any steam passes through the blast pipe, the valve ,is leaking. This may be due to uneven wear of the facing of the steam chest, which can be cured by filing and scraping it level ; or thekfault may be with the valve. In this connection it should be noted that a D slide valve, which is practically level when cold, may camber and leak. when hot, and for this reason the valves are often eased off slightly towards the ends with a scraper. The compound engine of the road locomotive or steam wagon presents a rather more complicated problem. Test the H.P. piston, and proceed as with' the single-cylinder engine. To test the H.P. sicln valve, close the ports as before and open the L.P. cylinder cooks. If, when the throttle is opened, steam is emitted from the L.P. cylinier cocks, the H.P. slide valve is leaking.
• As regards the L.P. piston and valve, open the bypass, and proceed as with a single engine.
,A double-cylinder single-expansion engine can be tested by disconnecting the valve at one side (by removing the eccentric rod pins) after putting the reversing levers into the centre notch and testing the other sidle, reversing the process to test the side not yet dealt with.