HINTS ON MAINTENANCE.
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How to Get the Best Out of a Vehicle, to Secure Reliability and to Avoid Trouble.
414.—Preventing Leakage from the Valve Caps of Tylor Engines.
We have in several hints referred to various methods for "preventing leakage caused by cracks in the cylinders between the valve caps of the. Tylor engine, this leakage often causing the copper asbestos washers to be cut through. We illustrate another device which is said to have proved very effective in preventing this trouble. This is made of 16 s.w.g. soft rolled copper, the valve caps being reduced in diameter to allow for the thickness of the flanges which project inwards. The pressure on the valve caps, and the expansion of the copper i when the engine s warmed up, are said to prevent all leakage of gas.
415,—Fitting Ball and Roller Bearings.
When fitting standard ball journal bearings care should be taken to ensure that the revolving race (usually the inner), is a tight fit on its seat to prevent "creep," or slow 'rotation of the race in relation to the shaft on which it is mounted. The revolving race, whether inner or outer, should be pressed home against a shoulder provided for the purpose, which insures true running of that part.
A ball bearing should be pressed into position wherever it is possible, but as it is not always possible to do this, a brass bush of a suitable size may be used to drive it home. Take care, however, to place the bush against the race that is to be driven, and direct ,fight blows as evenly as possible around the bush. Never attempt to direct the force of the drive on the balls and ball cage.
As ball journal bearings are intended for journal load only it is necessary that. either the inner or outer race be free endways to allow it to take up a position opposite the fixed race. The stationary race—usually the • outer—should be a nice push fit, perfectly free from shake, but not so tight as to prevent the balls moving it longitudinally if required. It is not uncommon to find that the shoulders on the shafts or in the housing are not machined to allow for' the end play, and , that the races of two bearings are pinched towards each other, which will put an enormous pressure on the balls. In cases where there is no end thrust, the shaft may be located by clamping endways the stationary race of one bearing only. The most lightly loaded bearing should be selected for this purpose.
When fitting roller journal bearings (parallel roller type) both the inner and outer race should be secured longitudinally. As with , ball journal bearings the B•12
revolving race should be a tight fit upon the shaft or housing on or in which it is mounted. It should be. noted that the shoulders between which the races Are clamped should not bear against the sides of the race to a diameter greater than the bottom or top of the roller track, or else nipping of the rollers endways will occur.
The stationary .race should be a good fit in its housing, free from shake and clamped endways, so as to ensure that the track of the rollers is in the centre of the race. It should be borne in mind that parallel roller journal bearings will take no end thrust whatever.
With ball thrust bearings the revolving race should be a nice fit on the shaft. The shoulder against which. it. abuts must be 'Perfectly square with the shaft and should be of such a diameter as to extend at least ha,lf way under the actual path of the balls, this is important, as a ithoulder of less than this diameter would _cause the ring to " dish."
416.—Preventing Cracks in the Cylinders of the Thornycroft.
One of our driver contributors informs us that about a year ago the back lug, by which the rear. cylinder, block of his Thornycroft engine is bolted to the crankcase, broke right oft. At the time he did not pay very much attention to the matter, putting the trouble down to a flaw in the casting, but during the recent hot weather a further two pairs broke in exactly the same manner.
Upon making investigations into the cause of the trouble, it was found, on removing the inspection plates from the cylinders, that the water jackets had become congested with sediment, and that practically no water was circulating. This was borne out by the fact that the paint outside the cylinders was scorched, and the cylinder walls were blue inside. It was therefore concluded that a piston must have seized up, and that the sudden jar thus caused had broken the lug.
In another case cracks occurred round the walls of the valve pockets of the back cylinder ; this trouble was put down to the same cause. It should therefore be made a practice frequently to remove the water jacket inspection plates and to keep the jackets, clean.