HINTS ON MAINTENANCE.
Page 66
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Checking Alignment in a Type J Thornycroft. Overhauling a Boiler Firebox. Dealing with Morris Valves.
Reducing Vibration on a Thornycroft.
CONSTANT usage, day by day, of the commercial vehicle in time makes itself felt in the driver's cab. A-little, end play in the wheels, too much backlash In the worm shaft, end play in the main shaft of the gearbox, and a general vibration about the chassis, which
gradually increases with wear and tear. On a Thornycroft type J chassis these faults can soon be remedied. For instance, packing washers in the wheels, a washer behind the thrust race on the worm shaft and a thicker brass pad at the front end of the main shaft will do wonders.
Excessive vibration is often due to the engine and gearbox being out of alignment with each other. To test for this fault it will be necessary to take the universal coupling leather from between the clutch and the constant-running pinion of the gearbox. Then a pointer can be arranged coming from the fork of the constant-running pinion and bent over so that it will travel around the side of the flywheel. This method will easily show the difference between the engine height and that of the gearbox, and the probability is that the engine Will be the lower. This is dye to the kear-side engine bearer and pin wearing, sometimes as much as -Pa in. Obviously a new bearer bracket and pin will be needed, although, if the means be available, bushing of the bearer bracket and turning down of the pin will be as good.
Thin sheet-iron under the supports of the engine or the feet of the gearbox will now bring the two into exact alignment, but, as a final precaution, bring the pointer around until it just touches the face of the flywheel. If this test shows engine and gearbox to be still out of alignment, an extra thin piece of tin under one corner of the gearbox will probably bring them dead inth line.
Attention should now be given to the universal coupling forks. If the cases of these be not square with each other and the holes not equally spaced, the leather will be twisted and pulled out of shape. The reSult will be short life for the leather and a clutch running out of truth.
In truing up the forks at the rear of the chassis it is advisable to spin the cardan shaft in the lathe, and, if necessary, spring it true. If the centre bolts in the rear springs be broken and the axle has moved back, have the springs attended to at once, as incorrect alignment of the rear axle does great damage to the cardanjoint leathers.
Removing Bulges from Boiler Fireboxes.
SHORTAGE of water or excessive scale in the boiler will often cause bulges to appear in the firebox and It is advisable to remove them at the first opportunity. One method of doing this is to remove the girder stays
and, employing a large blowlamp, make the bulges as hot as possible, preferably raising them to dull red heat. Now with a screw jack and a piece of fiat iron, the latter being placed against the bulge. and with the foot of the -jack against the other side of the firebox, the bulge can be forced out by screwing up the jack. Meanwhile, the blowlamp should be kept full on and the pressure applied slowly.
If necessary, a piece of iron or steel, shaped to the original surface of the firebox, may be substituted for the piece of iron as the bulge is forced out. An oxyacetylene lamp may be used instead of a blowlamp, but .care shOuld be taken to avoid local overheating. Bulges usually, occur in the roof of a firebox so that there is good support for the base of the jack.
While on this subject we would emphasize the importance of removing and cleaning the fusible plug about every three months, as it is due to this plug • failing to melt that bulging often occurs.
Broken stays also occur sometimes. They may be detected by testing with two hammers, one being held against the stay at one end whilst the other end is struck smartly with the second hammer,. A good stay will give a clear ringing sound, but if broken the sound will be deadened. Broken stays must be drilled out and new ones fitted.
Some Pointers on the Morris.
ON some models of the Morris there is a small
clearance between the fan-drive pulley on the camshaft and the drip pan, but this is not large enough to permit of the fan belt being slipped over the pullay. Removing the link screw and running the belt off and on again is an awkward job, and if the belt be left on the pulley after the fan is removed it is bound to become jammed against the cylinder casting as the crankshaft is rotated. This can be obviated by leading the fan belt over an old two-stroke motorcycle belt pulley-, securing the pulley to the radiator tie rod with string or wire.
If an extra washer be fitted to an old oil gun the gun will lift as well as force. Such a device is most useful for clearing oil from the bottom of the valve chest prior to removing the valves. This job will not be half so messy if the oil be removed first.
Before removing the valves bend a piece of tin, punch a bole through it and fix it on the front valve-door stud as shown in the sketch. This will prevent any possibility of a cotter or spring cap dropping into the sump through the space over the timing wlieei.
After re
: I • moving the
valves and before decar bonizing lay a piece of rag, over the tappet heads. The carbon chips and dust will then fall on to the rag,
instead of into tlia valve chest an can be removed.