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Fig. 406.—Table of Standard Fits for Ball Bearings.
cases of failure of wheel bearings have been directly attributed to rust caused by the indiscriminate application of a stream of water at 40 or 50 lbs. pressure per square inch which is not uncommon in many city water mains, to the parts of the car in which they are mounted. The water finds its way into the bearings, causes the highly finished surfaces of the balls and races to rust, and the extreme accuracy in manufacturing and the care of installing is fruitless in preventing breaking down of the bearings. The user will not deliberately clean off the parts of the power plant with a hose, the evil effects of water at this essential point having been hrought to his attention too forcibly by troubles in carburetion and ignition, yet the same person who is so extremely careful of the
motor, will spray other parts, fully as important in the duties they perform, with a stream of water under high pressure.
That rust is absolutely destructive to ball bearings has been thoroughly proven in so many instances that the contention cannot be questioned. Of what value is extreme accuracy of finish of the balls to .0001 of an inch if the advantages accruing are to be mitigated by deposits of rust of much greater thickness than the limit established in manufacturing. Such a condition can be as easily recognized by the novice as by the most expert for even if the bearing has been cleaned so that no ferric-oxide is visible to the eye, there will be a number of pits or depressions on the various parts of the bearings, especially at the highly finished ball surfaces, which are clearly evident. While these minute irregularities are sometimes caused by overloading and the flaking off of the metal which results from this condition, if due to causes other than rust and acid, the roughness would be confined to the ball tracks, whereas excoriations resulting from chemical action will be in evidence on all parts of the bearing.
It is a known fact that many oils and greases contain acids or alkalis, either as a necessary component of their chemical composition (as in some animal fats that contain stearic acid); as a part of some filler used to adulterate the oil or alter its viscosity, and sometimes as a residue of some of the processes of purifying that obtain in refining from the crude product. The presence of acid in lubricants will cause an etching with irregular edges, in contrast to the clearly defined rust marks. A good lubricant for bearings is a slush made of pure vaseline and lighter mineral oil this being heated to make its viscosity less and enable it to penetrate all parts of the bearings, no matter how minute the spaces. When the bearing has been dipped in this and allowed to remain long enough to permit the oil to reach all parts, it is taken out and allowed to cool and the surplus lubricant is wiped off the outside. Such a mixture will stay in place and will not run out like lighter oils, and at the same time its viscosity is not so high that it will produce unnecessary friction.
How Bearings Should Be Cleaned before Examination.- Another point that can be criticized is the common method of clean
ing ball bearings in the average car repair establishment or machine shop. They are often dipped in dirty gasoline in which old gears and other parts have been previously cleansed, and this material is often so full of metallic particles, that as soon as it is stirred up enough to disturb the sediment, instead of having a clean bearing, one has filled it with deleterious substances without knowing it. A simple solution of common washing soda and hot water, such as is used in many shops for cleaning greasy parts and assembled bearings at the completion of the manufacturing process offers important advantages. This can be easily made by taking about a handful of the soda to the pail of boiling water. The cleaning agent should be kept nearly at boiling point while in use. The bearings are placed in a wire basket, or hung on a wire and dipped in an alkali solution a few times to remove all dirt; then they are immersed in clean kerosene and given a swirling motion to have this material thoroughly clear out all traces of the soda. The bearings should not be allowed to remain in the wash more than a few minutes at the most, and a few dippings are all that is necessary to clean them out thoroughly and cut all the hard and rancid grease or remove any metallic dust present. After examination of used parts, if the bearings are clean, the surfaces bright and there is not too much looseness, they are in good condition.
A little attention given to careful inspection and consistent lubrication of bearings will be amply compensated for by the increased service obtained and augmented efficiency. The important rules upon which efficient ball or roller bearing service is based can be summed up in a very few words.
First, inspect the bearings from time to time and see that they are clean, and the lubricant does not contain foreign matter, especially in gear boxes and differential casings.
Second, be careful in supplying new lubricant that it is free from acid, alkali, vegetable or animal fillers or other deleterious substances.
Third, when installed in exposed parts of motor cars, be careful when washing not to direct the stream of water directly against bearing housings of the parts.
Brake Forms and Adjustments.-The brakes used to retard
motor car motion are a part of the car that are not only used, but which are often apt to be abused. Brakes are of two general forms, the internal type as shown at Fig. 407, A, and the external constricting band type as exemplified by the outer brake of the assembly shown at Fig. 407, B. Internal brakes may be either metal shoes that are in metallic contact with the brake drums attached to wheel hubs when applied, or members faced with some asbestos frictional material which can be replaced when worn. The internal brakes may be cam expanded as the forms shown at A are or may be worked by a wedge expander as the internal brake expanders of the assembly shown at B. As a rule no adjustment is provided on cam expanded brakes in the brake construction itself. On external brakes, means of adjustment are usually included.
When full movement of a hand lever or pedal fails to engage an internal brake the first step is to remove the wheel to make sure that the slipping is not due to deposits of grease or to worn brake facings. If the brake facing is clean and not worn unduly, the only practical means of adjustment is by tightening up on the operating linkage. This is easily done by shortening the brake control rod. In the construction shown at Fig. 408, B, this is easily accomplished by turning up on a turnbuckle set into the brake rod. In all cases, even if the turnbuckle is not provided, the clevis at the end of the rod may be screwed up further on the rod which has the same effect as shortening the rod by a turnbuckle would have.
Care should be taken in adjusting brakes by altering the length of the brake rod to have the brakes on both wheels take hold at the same time. In the construction shown at Fig. 408, A, this may be done by unloosening the clamp bolts and setting the lever operating the right brake at the proper point in the slot of the master lever which also operates the left brake. On an external brake of the form shown at Fig. 408, C, the means of adjustment is readily perceived. With an external constricting brake it is merely necessary to reduce the circumference of the brake band by screwing up an adjustment to provide for minor depreciation of the brake lining.
On the Overland cars, when it is desired to adjust the brakes this is easily done by loosening a clamp bolt passing through the