For cylinder lubrication American mineral oil is preferable to Russian oil. The specific gravity should lie somewhere between .886 and .889 at 70 degrees F.
Oil of this quality begins to evaporate at about 365 degrees F. Ignition occurs at 535 degrees F. The point of complete combustibility lies between 625 and 645 degrees F. Oil of this quality solidifies at 39 or 41 degrees F. Its color is a reddish yellow with a greenish fluorescence. Compared with water its degree of viscosity lies between 11.5 and 12.5 at a temperature of 140 degrees F.
Before lubricating other parts of the engine with oil that has been used for the piston, heavy particles and foreign matter, such as dust, bearing incrustations, and the like, should be filtered out. The piston-pivot and the connecting-rod head are preferably lubricated with fresh oil, because their constant movement renders inspection difficult and the control of lubrication irksome. A good, industrial mineral oil of usual market quality will be found satisfactory. In order to bring home the importance of employing good cylinder-oil and of proper lubrication the author can only state that in his personal experience he has frequently detected losses varying from 10 to 15 per cent. in the power developed by engines poorly lubricated.
Types of Lubricators.—Among the more common apparatus employed for automatically lubricating the cylinder, the author mentions an English oiler of the type pictured in Fig. 67 which is driven simply by a belt from the intermediary shaft, and which rotates the pulley P secured on the shaft a of the apparatus, at a very slow speed. The shaft a is provided at its
end with a small crank, from which a small iron arm f is suspended, which arm dips in the oil contained in the cup G of the oiler. When the shaft a is turned this arm, as it sweeps through the oil-bath, collects a certain quantity of oil which it deposits on the collector b. From this spindle the oil passes through an outlet-pipe opening into the bottom of the oiler, and thence to the cylinder. The entire apparatus is closed by a cover D which can be easily removed in order to ascertain the quantity of oil still remaining in the apparatus. Many other systems are utilized which, like the one that has been described, enable the feed to be controlled. Often small force-pumps are employed as cylinder-lubricators. Whatever may be the type selected, preference should be given to that in which the feed is visible (Fig. 68).
Fig. 67.—An automatic English oiler.
If the oil be fed under pressure the cylinder is more constantly lubricated. Pressure-lubricators are nowadays widely used on large engines. It is advisable to
add a little salt to the water contained in sight-feed lubricators so that the drop of oil is easily freed.
These oil-pumps are provided with small check-valves at their outlets as well as at the inlets of cylinders. In order that pressure-lubricators may operate perfectly they should be regularly inspected and the check-valves ground from time to time.