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HINTS ON MAINTENANCE.

7th February 1922
Page 26
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Page 26, 7th February 1922 — HINTS ON MAINTENANCE.
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CONTRIBUTIONS 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 garage practice in the maintenance of a vehicle—practices (This hint applies to Dennis vehicles with chassis numbers between 8,000 and 12,000.)

No definite figures as to mileage can be guaranteed on any make of commercial vehicle unless certain conditions can be complied with, and these, in practice, can seldom occur together. High speeds are very detrimental, other variable factors being road resistance, condition of the vehicle, overloading, wind pressure, and the use of trailers, whilst the mileage can certainly he improved by careful driving. The result is that the mileage per gallon of fuel May vary between six ainj nine and a half. In order to improve the consumption, the inlet pipe should be removed from the engine and its bottom section (which is the superheater) disconnected. This latter is a press fit into the top aluminium branch, and can be taken apart after removing the four cap nuts on the circular plate. The governed gear should be permanently removed from the pipe and plugs carefully soldered into the spindle holes.

At the positions where the water enters and leaves the superheater a f in. drill should be inserted and the inlet pipe drilled clean through. A copper liner 524 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,

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must be made out of 11 in. diameter copper tubing of is s.w.g. ; the top and bottom ends of this require shaping, and it may be preferable to purchase a ready-made pipe from the manufacturers or even to send the superheater and have it fitted by them. This liner fits inside the original induction pipe and is secured at each end by soldering, but the latter must be well done, otherwise it will result in leakage of water.

The effect of fitting this liner increases very considerably the velocity of the mixture, with the result that a petrol jet at least one size smaller can be fitted to the •carburetter, whilst there is an appreciable difference both in petrol consumption and acceleration.

The carburetter recommended for the engine is the Claudel-Hobson :30 mm. A.C. type, with a 1.35 mm. jet, but if the liner is fitted a 1.30 mm. jet may be used.

By chilling through the original inlet pipe, hot water is permitted to reach the liner, consequently -the jacketing remains effective. There are two types of superheaters in use, one having 'detachable side plates, which are preferable, as they facilitate cleaning, also they can be removed and the inlet pipe punctured in several places to allow more freedom for the water to cireulate round the liner. The other type has fixed side plates. The various rods and levers working the governor gear should be removed, except in the case of the long lever nearest the timing gearcase. The most satisfactory speed for this type of vehicle, so far as fuel economy is concerned, is 17 m.p.h.

163.—Removing a Leyland Camshaft.

Although not often necessary, it is sometimes useful to know how, the camshaft can be removed from a Leyland engine without totally dismantling the whole unit.

To draw out the camshaft, first slack off the front camshaft and bearing setscrew, which will be found on the crankcase just below the forward end of the front cylinder block. Next remove the small inspection cover for the oil pump driving gears, and tap out the taper pin fixing the gearwheel pump driving shaft. This wheel can then be removed, allowing the taper pin on the front wheel of the camshaft. to be extracted. Finally, take off the cam gear cover on the front of the engine and it will then be found that the camshaft can be taken out quite easily.

Care should be taken to see that the tappets are lifted from their seatings in order to allow the cams to pass the rollers on the valve push-rods.

164.—The Valve and Valve Caps on the Bristol.

As regards the valves in the Bristol engine, these are made from special tungsten steel, which has proved to give very long life, in hard service. These valves are extremely hard, and on this account it is unwise to grind out any pit marks on them in their seatings, as this means sacrificing a great deal of the cast-iron of which the seating is formed. It is

preferable first to dress the valve face in a valve truer or lathe, after which a very little grinding will suffice to make a perfect fit.

The Bristol valve cap iS" of the quickly detachable type, being composed of a valve head held down on to its seating by means of a large diameter plug screwed through the centre of a breech block. When

the screwed plug is slacked back, the breech block nyny be revolved a quarter turn and removed to permit of the valve eap proper being lifted out.

Sometimes the latter is found to be cemented into position by carbon deposit, but a sharp turn of the engine, to create _pressure inside the cylinder, will usually force it off its scat.

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Locations: Bristol, London

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