the gears, or sand loosened from the interior of the gear case or rear axle housing castings. In sliding gears, especially when operated by an inexperienced person, there is a constant clashing of the pinions in changing speed, which tends to loosen particles of metal from the teeth. These fall into the lubricant, and are churned around and often find their way into the ball races. The

132006

127 005

102 004

076 003

05 002

025 001

000 000

025 001

10 INCHES

10 20 30 40 50 60 70 00 30 100 110 120 130 140 150 160 170 180 190 200 zio zło 230 240 250 MILLIMETERS SHAM IS OVERSIZE TO LIMITS GIVEN

Fig. 405.-Chart Showing Driye Fits for Ball Bearings, etc. rapid failure of the bearing is the inevitable consequence. The importance of proper mounting has been so firmly impressed upon the automobile manufacturers that but little trouble is caused from improper installation in cars of reputable makes. Hence we are forced to consider the user in many cases when analyzing causes of bearing failure.

There is a condition that is beyond the control of the manufacturers of either the bearings or the mechanism to which they are fitted, and that is the use of impure oils, and carelessness in washing the running gear and other parts of automobiles. Many

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 brought 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 composi tion (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 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