Only very light clean oil, or vaseline should be used on ball-bearings, as heavy greases and solid lubricants pack in the races and cause binding or breakages.
Flake graphite is much used as lubricant, and too much cannot be said in its favor, as it furnishes a smooth, even coat over the shaft, fills up small scores and depressions, and makes the use of light oil possible under heavy bearing pressures. With graphite, less oil is used, as the graphite is practically permanent, and should the oil fail for a time, the graphite coat will provide the necessary lubrication until the feed is resumed without danger of a scoring or cutting. In fact, when graphite is used, the oil simply acts as medium by which the graphite is carried to the bearings.
If graphite is injected into the cylinder in small quantities it greatly improves the compression, as it fills up all small cuts and abrasions in the cylinder walls.
A good mixture to use for bearings is about 1½ teaspoonsful of graphite, to a pint of light machine oil, thoroughly mixed.
Graphite can be placed in the crank chamber of a splash feed engine, by means of an insect powder gun.
Trouble with oil cups is always in evidence during cold weather, as the oil congeals, and does not drip properly into the bearings. The fluidity of the oil can be increased in cold weather by the addition of about ten per cent of kerosene to the oil.
If too much oil is fed to the cylinders, the piston rings will be clogged with gum, and a loss of compression, or a tight piston will be the result. An excess of oil will short-circuit the igniter or sharp plugs, and will form a thick deposit in the combustion chamber that will eventually result in preignition or back-firing. Deposits and gum formed in the cylinder will cause leaky valves and a loss of compression. Feed enough oil to insure perfect lubrication, but not enough to cause light colored smoke at the exhaust.
Lubricating systems may be divided into three principal classes: Sight-feed, splash system, and the force feed system. Sight feeding by means of dripping oil cups is too common to require description, and is used on many stationary engines, both large and small.
The splash system is in general use on small high speed engines both stationary, and of the automobile type.
The force feed system in which oil is fed under pressure by a pump is by far the most desirable as the amount of oil fed is given in positive quantities proportional to the engine speed, and with sufficient pressure to force it past any ordinary obstructions that may exist in the oil pipe.