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HINTS ON MAINTENANCE.

13th December 1921
Page 30
Page 31
Page 30, 13th December 1921 — HINTS ON MAINTENANCE.
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How to Get the Best Out of a Vehicle, to Secure ,Reliability and to Avoid Trouble.

CONTRIBUTIONS are invited for this page from fleet managers, drivers, garage foremen, and mechanics, works staff and draughtsmen, 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 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. 1."

132.—Fitting Dennis Big-end Bearings. All but the very early models of Dennis engines have connecting rods provided with oil scoops. In fitting the white-metal-lined bearings of the big-ends, care should be taken as to the direction in which the oilways run. . The bottom half bearing has oil grooves .as shown in the diagram, and, when assembling, the following points should be noted. The scoops are, of course, faced in the direction of rotation, and the oil grooves in each bottom half or cap of-the bearing should be in the same direction as the scoop. The reason foe this is that the motion of the crankpin tends to wind the oil round in the direction in which it is rotating. If this procedure is carried out, much trouble will be saved, as, unless care be taken, the bearings may run when heavily stressed.

133.—Stocking Undersized Bearings.

The engineer in charge of a fleet of vehicles is faced, after these vehicles have been running for a certain time, with the problem of providing oversized pins, etc., and undersized bearings, winch will allow for the boring out or'.regrinding of parts in order to .ensure perfect fits after considerable, wear. Many of the motor vehicle, manufacturers themselves stock parts-made to second or third standards, but in some cases this is not done, and the engineer must supply these himself. When 'this is so, it is essential, for the sake of efficiency, to ensure that the various fresh standards are real standards and not merely parts made to fit certain jobs. This is of particular importance where the fleet consists of only one or two makes of vehicles. In such instances it is advisable to keep exact models of the new standards.. For instance, in the case of a reground crankshaff, either an old crankshaft or a bar of metal turned down to the exact size of the reground shaft may be kept in stock, and to this the new big-end and main bearing brasses can be fitted. These may then be returned to stores for future use, or one or more pairs can be supplied to each driver as spares in case of breakdowns on the road. It is also always advisable to keep accurate and permanent records olethe changes made, and this should be stipulated to the transport manager by the owners of the vehicles, as, although certain members of the staff may knew of the changes which have taken place, it must always be remembered that no staff can be considered as absolutely permanent, and where any changes occur ih the peri.onnol, the records kept by individuals may easily be lost. The chart reproduced with this hint shows what can be done in this direction.

134.—Testing Oil Circulation on Dennis. .

In those types of Dennis engines in which the magneto and water pump are carried across the top front of the timing case the ciroulation of the oil can he tested by disconnecting one end of the / in. drain pipe which feeds the cross drive. The engine should be aecelerated slightly when the pipe is disconnected, and as this pipe is almost at the ,end of the circulating system, if oil is delivered it is a good indication that the remainder of the system is working .correctly_ In later types of engines, where the magneto and water pump are parallel with the camshafts, the test should be made by 'loosening for a few threads the setscrew which holds' the water-circulation pump in position. It is not necessary to take this setscrew right out. Other means of testing the system are by the removal either of the brass cap of the oil-release valve or' the oil-pressure gauge from its column, the engine being accelerated slightly in each instance. Of course, such tests are only required if the oilpressure gauges are not functioning correctly.

135.—Removing Differential Gear on type P Halley.

If at any time it is found necessary to remove the worm and differential gear from the rear axle on the six-cylinder type P Halley chassis, first remove the driving caps from the rear wheels and withdraw the differential shafts in the usual manner. These shafts have holes. tapped in them so that a bolt may be inserted and a good pull thus given. After this the holding-down nuts on the back-axle casing should be unscrewed and the universal fabric joint broken. The whole gear can then be taken out.

A most important point occurs in the replacement of this gear. It should be noted whilst doing this that the gear is carefully replaced, in order to secure true centring between the worm and worm wheel.

On each side, between the outer race of the ballthrust washer and the wall of the casing, is an adjusting washer, which has been carefully ground to size to effect the correct centring. These washers must, therefore, be replaced most carefully, and

great care must be _taken not to exchange them. If such an exchange has been made by accident, it will be found that the dowel pins on them are specially 'placed in different positions, so that none but the correct washers can satisfactorily be employed, and, therefore, if at any time it is found that the washers do not bed down correctly, do not endeavour to make them do so by employing force, first make certain that they have not inadvertently been changed.

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People: Dennis Big
Locations: London

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