(116) General Notes on Lubrication.

No matter how carefully the surface of a shaft or bearing may be finished, there always remains a slight roughness or burr of metal, which although of microscopic proportions is productive of friction or wear. Each minute projection of metal on a dry shaft acts exactly as a lathe tool, when the shaft revolves in cutting a groove in the stationary bearing. Since there are a multitude of these projections in a journal, the wear would be very rapid, and would in a short time completely destroy either the shaft or bearing, no matter how highly finished in the beginning.

When lubricating oil is introduced into a bearing it immediately covers the rubbing surface, and as the oil has a considerable resistance to being deformed, or is “stiff,” it separates the surface of the shaft from that of the bearing for a distance equal to the thickness of the oil film. With ordinary lubricants this distance is more than enough to raise the irregularities of the shaft out of engagement with those of the bearing. This property of “stiffness” in the oil is known as “viscosity.” The value of viscosity varies greatly with different grades of oil, and also with the temperature with the result that the allowable pressure on the oil per square inch also varies. With oils of low viscosity a small pressure per square inch on the bearing will squeeze it out, and allow the two metallic surfaces to come against into contact, causing wear and friction, while an oil of greater viscosity will successfully resist the pressure.

The life and satisfactory operation of the engine depends almost entirely upon the lubricant and the devices that apply it to the bearings. Excessive wear and change in the adjustments are nearly always the result of defective lubricating devices or a poor lubricant. The principal lubricants are:

(1) Solid lubricants such as graphite, soapstone, or mica.

(2) Semi-solid lubricants such as vaseline, tallow, and soap emulsions, or greases compounded of animal fats, vegetable and mineral oils; and

(3) Liquid lubricants, such as sperm oil, or one of the products of petroleum, the latter medium being the class of lubricant most suitable for internal combustion engines, owing to its combining the qualities of a high flash-point with a comparative freedom from either acidity or causticity.

Oils of animal or vegetable origin should never be used with gas engine as the high temperatures encountered will char and render them useless. Tallow and lard oil are especially to be avoided, at least in a pure state.

In the cylinder only the best grade of GAS ENGINE cylinder oil should be used, which according to different makers has a flash point ranging from 500 to 700 degrees. Using cheap oil in the cylinder is an expensive luxury. In general, the oils having the highest flash points have also the objectionable tendency of causing carbon deposits in the combustion chamber and rings which is productive of preignition and compression leakage. The lower flash oils have a tendency to vaporize and to carry off with the exhaust which will leave the walls insufficiently lubricated unless an excessive amount is fed to the cylinder. By starting with samples of well known brands recommended by the builder of the engine it will be an easy matter to find which is the cheapest and gives the best results. In figuring the cost of oil do not take the cost per gallon as a basis, but the cost for so many hours of running, or better yet the number of horse-power hours. Unless you are fond of buying replacements and new parts do not stint on the oil supply.

On the other hand, an excess of oil should be avoided as this means not only a waste of oil through the exhaust pipe, but trouble with carbon deposits and ignition troubles as well. Foul igniters, misfiring, and stuck piston rings are the inevitable result of a flood of lubricating oil. When a whitish yellow cloud of smoke appears at the end of the exhaust pipe, cut down the oil feed. The exhaust should be colorless and practically odorless.

Too much oil cannot be fed to the main bearings of the crank shaft if the waste oil is caught, filtered and returned to the bearings by a circulating system, for the flood of oil not only insures ample lubrication but removes the heat generated as well. The bearings require a much lighter oil, of a lower fire test than the cylinder oil. It is evident that its viscosity is a most important element, as it determines the allowable pressure on the shaft. The viscosity of an oil varies with the temperature and is greatly reduced at cylinder heat. A comparative test of the viscosity or load bearing qualities of an oil may be made by making bubbles with it by means of a clay pipe; the larger the bubble, the higher the viscosity of the oil.

Different sizes of bearings, and bearing pressures, call for oils of different viscosities, and consequently an oil that would be suitable for one engine would not answer for another; heavy bodied oils being used for heavy bearing pressures, and light thin oil for small high speed bearings. The best way to determine the value of an oil for a particular shaft bearing is by experiment, attention being paid to its adaptability for the feeding devices used.

The compression attained in a gas engine cylinder depends to a certain extent upon the body of the cylinder oil, for many engines that leak compression past the rings with thin oil will work satisfactorily with a heavy viscous oil that clings tightly to the surfaces. An engine will often lose compression when an oil of poor quality is used.

Air cooled engine cylinders require an oil of heavier body than water cooled because of the higher temperature of the cylinder walls. Gum and sticky residue are usually formed by animal oils or adulterants added to the numeral oil base. Oils containing free acids should be avoided as they not only corrode and etch the bearing, but also clog the oil pipes or feeds with the products of the corrosion.

Free acid is left from the refining process, and may be determined by means of litmus paper inserted into the oil. If the litmus paper turns red after coming into contact with the oil, acid is present, and the oil should be rejected.

The following are the characteristics of an oil suitable for use on an engine:

(a) The oil must be viscous enough to properly support the bearings or to prevent leakage past the piston rings.

(b) It should be thin enough so that it can be properly handled by the oil pumps, or drip freely in the oil cups.

(c) It should not form heavy deposits of oil in the cylinder and cause the formation of “gum.”

(d) It should contain no free acid.

Ordinarily a good grade of fairly heavy machine oil will be suitable for use on the bearings of the average engine, such as the cam-shaft and crank-shaft bearings.

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.

Another system that is half splash, and half force feed, is the pump circulated system much used in automobiles.

THE SPLASH FEED SYSTEM is the simplest of all, as the bearings are lubricated by the oil spray caused by the connecting rod end splashing through an oil puddle located in the bottom of the closed crank case. The piston and cylinder are lubricated by the spray, as well as the bearings, as the lower end of the piston projects into the crank chamber at the moment that the connecting rod end strikes the oil puddle.

To maintain constant lubrication, it is necessary that the oil in the puddle be kept at a constant height, or as in some cases be varied in such a way that the surface of the puddle is raised and lowered in proportion to the load on the engine. In the average engine the oil level is maintained by overflow pipes or openings that allow any excess of oil over the fixed level to flow back to the pump. In the Knight engine the puddles are formed in movable cups which are connected with the throttle in such a way that the opening of the throttle raises the oil level and supplies more oil to the engine at the greater load, or speed.

Oil in splash systems is supplied by a low pressure pump, usually of the rotary type, in the base of the engine. Oil from the pump passes to the bearings, drops into the puddle, overflows through the overflow opening, and returns to the pump through a filter, the same oil being used over and over again until exhausted. This strainer should be removed occasionally and the dirt removed, for should it be allowed to collect it is likely to obstruct the oil supply. The oil should be replaced before it becomes too black or foul, the crank case and bearings thoroughly cleaned with kerosene, and new oil replaced. The supply may be interrupted by the failure of the pump, caused by sheared keys or leakage of air in the suction line due to cracks. It would be well to run the engine for a few minutes with the kerosene in the crank case, in order that all of the oil may be removed. See that the drain cock is closed at the bottom of the cylinder or all of the oil will be lost. Lock the valve handle carefully so that it cannot jar open. If light colored smoke appears in intermittent puffs with a multiple cylinder engine, it indicates that one cylinder is receiving too much oil.

The force feed system is by far the most reliable of all oiling systems, as it feeds uniformly and continuously at almost any temperature, and against the pressure of practically any obstruction in the pipe.

The oil is supplied by a small pump driven from the engine, the pump being incased in the oil tank housing. Frequently a hand pump is used in combination with the power pump when starting the engine, or at times when the power pump is out of service. A single pump is used with any number of leads, each lead, or feed, having an independent regulating valve and sight feed, or a pump unit may be provided for each lead, depending on the size of the engine.

(118) Bosch Force Feed Oiler.

The force feed of the Bosch Oiler is so positive in character, that the flow of oil is not affected by heavy back-pressure due to elbows and the diameter of the conducting pipes. Springs, valves and other devices, which would check the flow of oil, are fundamentally eliminated. The amount of oil fed may be accurately and permanently regulated. Glands and other packings and bushings are eliminated. Connecting rods and all links are eliminated by the direct application of the movements of the oscillating cam disks to the pump plungers and piston valves.

Each feed of this oiler is provided with a separate pump element consisting of a pump body plunger and a piston valve, the suction and feed ducts connecting directly with the pump body of their respective elements. With this construction, pump elements may be replaced or added. The oiler requires no attention other than to be supplied with oil; and the opening and closing of the valves, pet cocks, etc., on starting and stopping the machine is rendered unnecessary. The correct and regular operation of the elements may be verified by observation of the reciprocating movements of the regulating screws.

Each pump plunger is provided with an adjusting screw through which the feed may be regulated from 0 to 0.2 cubic centimeters for each stroke.

The Bosch Oiler (Fig. 121) being positively driven by the machine that it supplies, the oil fed is in all cases proportional to the engine speed; overloads are thus automatically taken care of.

The circular arrangement of the elements of the Bosch Oiler permits the device to be driven by a single shaft, and the oil is forced through the feeds from a single reservoir to the required points of application. A pump element consists of a pump body 1, a pump plunger 2 and a piston valve 3, and is supported on the base plate 13. The elements are arranged concentrically about the drive shaft in such a manner that the pump plungers form a circle around the circle formed by the piston valves.

The pump cam disk 20 and the valve cam disk 22 are set on the drive shaft at other than a right angle with its axis, and the rims of the disks are gripped by slots formed in the heads of the pump plungers and piston valves. The relation of these cam disks is such that the valve cam disk is 90° in advance of the plunger cam disk. The valve cam disk is solid on the drive shaft, but the pump cam shaft is loose and driven through a lug on the valve cam disk. When the drive of the pump is reversed, the lug on the valve cam disk frees itself and again takes up the drive of the pump cam disk, after the drive shaft has made a half revolution.

Regulating screws 4 are set in the slotted heads of the pump plunger, and by means of this the back-lash or play of the cam disk may be regulated. The regulating screws are provided with lock nuts, and project through the cover of the oil tank housing, being exposed by the removal of the filler cover 42. The filler opening is provided with a removable strainer to prevent the entrance of foreign particles into the oil tank.

Pump shaft 14 is driven through worm gear 23 which meshes with worm 24 on drive shaft 25; drive shaft 25 projects from the oiler housing, and is coupled with the driving shaft of the machine to be lubricated.

Base plate 13 is attached to the oiler cover by three stud bolts, thus permitting the removal of the entire oiler mechanism from the housing.

The quantity of oil in the oil tank is shown by gauge glass 44.

On the starting of the machine to which the oiler is attached, the pump shaft and the cam disks that it supports are set in motion through worm 24 and worm gear 23. A direct reciprocating motion is given to the pump plunger and to the piston valve by the rotation of the cam disks which have a movement similar to that of the “wobble saw.” The relation of the cam disk is such that the piston valve movements are 90° in advance of the movements of the pump plungers. The pump will run in either direction without alteration.

To secure this effect a play of 90° is provided between the cam disk. When cam 22 is driven clockwise, cam disk 20 is driven by the lug which meshes with a lug on disk 22. The cams are then in such a relation that the cam valve disk is 90° in advance of the pump cam disk. When reversed, cam 20 remains at rest until cam 22 catches the lug and cam 20, when the drive continues as before. The cams are then in the same relation as previously for as the valve disk 22 has traveled through 180° it is evident that it is 90° in advance of the pump disk.

(119) Castor Oil for Aero Engines.

Castor oil is used almost exclusively in the Gnome and other rotary engines of the same type, but has not been particularly successful on stationary cylinders.

Chemically, castor oil differs from all other vegetable or animal oils in containing neither palmitin or olein. It is soluble in absolute alcohol, but practically insoluble in gasoline. On the other hand, the castor oil is capable of dissolving small quantities of mineral oil, the more fluid they are the less it absorbs of them. But the insolubility of castor oil in mineral oil disappears completely when it is mixed with even a very small quantity of another vegetable or animal oil, such as colza or lard oil. An adulteration may thus result in a serious reversal of the oil’s best qualities; in fact, in serious seizures, Castor oil does not attack rubber, but it contains 1 to 2 per cent of acid fats; sometimes more.

“In my opinion says a writer in ‘Autocar’ castor oil can only be used in fixed cylinders with impunity for short distances and then with repeated cleanings between runs, but on rotary engines of the Gnome type cleaning is almost unnecessary. The reason is that one cannot consistently use castor oil over and over again, for the fact is indisputable that it has a far greater tendency than mineral oils to absorb oxygen, and so gradually to increase in body and finally to gum. When once it commences to gum the carbonization becomes more rapid, because the thickened and pitch-like oil acts as an insulating covering on the top of the pistons and of the cylinder, and cannot get away with sufficient rapidity to avoid decomposition and baking to a coke. Therefore if castor oil is to be used on the ordinary stationary cylinder type of engine, it is necessary to wash out the crank chamber and to replace with fresh oil at frequent intervals. On a rotary engine such as the Gnome this cleaning is unnecessary, because there is a continuous stream of fresh castor oil brought into the crank chamber and then thrown by centrifugal force past the pistons and through the cylinder into the exhaust. Thus the stream of oil never has sufficient time to oxidize fully, gum or decompose. This action of centrifugal force accounts for the large consumption of oil on the rotary engine, and also for the fact that the pistons and cylinders keep comparatively clean.

“In thus criticizing the use of castor oil I do not wish it to be inferred that it is not an excellent lubricant. What I wish to suggest is that in the case of an internal combustion engine it must be made with discretion. A point in favor of castor oil is the fact that it maintains its viscosity in a remarkable manner at high temperatures, and that at those high temperatures it has a peculiar creeping or capillary action which enables it to spread uniformly over the whole of the metallic surfaces, whereas under the same conditions a similarly bodied mineral oil would be unevenly distributed in patches. Another point is that the specific heat of castor oil is considerably higher than that of a pure mineral oil. This is in its favor, insomuch that it shows castor oil to be a better heat remover than a mineral oil.

“Motorists and aviators have from time to time informed me that they are using castor oil, but have apparently been under some misapprehension. I find that they have been using a brand of prepared oil under the impression that it is a specially refined castor oil, or that it is a blend of castor oil.”

A simple method for testing the purity of castor oil is at the disposal of all. It is known as the Finkener test. Ten cubic centimeters of castor oil is placed in a graduate. Five times as much alcohol, 90 per cent, is added and stirred in. The solution should remain clear and brilliant at 15 to 20 degrees C. An admixture of foreign oils, even if only 5 per cent, riles the solution at this temperature, though not above it.

(120) Force Feed Troubles.

The most common trouble with force feed systems is the failure of the operator to remove the dirt collected by the strainer. The oil piping should be cleaned out at least once every year by means of a wire and gasoline, to remove any gum that may have been deposited. Driving belts should be kept tight to prevent slipping, and belts that are soaked with oil should be cleaned with gasoline and readjusted.

Leaking pump valves generally of the ball type are a common cause of failure. They may leak because of wear or by an accumulation of grit and dirt on their seats, which prevents the valves from seating properly. If the valves leak, the oil will be forced back into the tank, or will not be drawn into the pump cylinder at all, depending on whether the inlet or discharge valve is the offender. Plunger leakage which is rare will cause oil failure.

If the oil pipes that lead to the bearings rub against any moving part, or against a sharp edge, a hole will be worn in the pipe, a leak caused which will prevent the oil from reaching the bearing. A dented or “squashed” pipe will prevent the flow of oil.

The set screw or pin holding the pulley to the pump shaft may loosen and cause it to run idly on the shaft without turning the pump. This will of course, prevent the circulation of oil.

The worm and worm wheel may wear so that the pump is no longer driven by the pulley shaft, or a poor pipe connection may leak all that the pump delivers.

The amount of oil required by each lead or bearing should be carefully determined by experiment, and kept constantly at the right number of drops per minute.

The feed adjustments jar loose, and should be inspected frequently.

(121) Oil Cup Failure.

Oil cups should be cleaned out frequently with gasoline or kerosene, as any gum or lint will interfere seriously with the feed. They should be adjusted and filled frequently to prevent any possible chance of a hot bearing.

Oil cups should be as large as possible in order that they may be left for considerable periods without danger of a hot box.

Cold weather affects the oil feed to a considerable extent, especially with small oil cups, and they should be kept as warm as possible. When heavy oils are used a cold draft will stop the feed.

Oils may be made more fluid in cold weather by the addition of about ten per cent of kerosene.

(122) Hot Bearings.

A hot bearing is almost a sure sign of insufficient oil, and the trouble should be located and remedied immediately. Oil pumps stopping, clogged oil pipes or holes, frozen oil, or oil leaks are common causes of hot bearings.

Never allow an engine to run with a hot bearing for any length of time, as the bearing or piston may seize tight and wreck the engine. Inspect the journals frequently to see if they are above normal temperature. A hot, binding bearing often causes the effect of an overload on the engine, slowing it down, and increasing the governor and fuel feed, this is followed in a short time by the bearing seizing.

(123) Cold Weather Lubrication.

It is by no means uncommon trouble in cold weather to find excessive fluctuations in pressure as the engine speed and temperature of the oil varies. Thus, if the pressure be set correctly with the engine running fast, and when just started up, it will be found, after half-an-hour’s running, that, with the engine turning slowly, the pressure is far too low, owing to the oil having become thin. If the pressure be then reset, it may be found on next starting up from cold that the gauge goes hard over, and may very easily be burst if the engine is run fast.

The point is one to which many designers of engines pay far too little attention, though the difficulty may be very easily gotten over. The secret lies in having the by-pass outlet of most ample proportions, so that the excess of oil, however thick, can get away quite easily. If there is any throttling of the by-pass, back pressure must result with consequent increase of the pressure at which the by-pass valve comes into operation. In other words, the pressure of the main supply to the bearings will be increased.

A writer to “The Motor,” London solved this problem in the following manner:

“Originally, the by-passage was somewhat small, little larger than the oil delivery pipe to the engine, which was about 3
16 inch bore, and the result was that the pressure when starting with the oil cold rose to about 25 pounds per square inch, and fell to about one pound per square inch with the oil hot and the engine running slow. It was possible, however, to bore out the by-pass passage and fit a larger pipe, about three times the area of the main delivery pipe, with the result that the oil, when cold, never rose above about 15 pounds per square inch, however fast the engine run. When thoroughly heated, the normal running pressure was about 6 pounds per square inch, falling to 2 pounds per square inch with the engine only just turning over, which brings up the question of the correct working pressure. This will vary very largely with the design of the engine, but, broadly speaking, the higher the pressure the better for the bearings. The limiting figure is determined by the tendency of the engine to throw out oil at the end of crankshaft bearings, and by the amount that gets past the piston rings. Obviously, an engine with new, tight bearings and new piston rings will stand a higher pressure without undue waste of oil or excess deposit in the cylinder head than will an old engine with worn bearings and slack rings. And, again, the question will be affected by the design of the pistons. For instance, where the trunk of the piston is bored for lightness, much more oil will get past the rings than in cases where a ‘solid’ trunk is employed. Roughly speaking, 8 to 15 pounds per square inch is a good figure for a new, high-speed engine. An old and worn engine, particularly if not of a high-speed type, may require no more than 2 to 6 pounds per square inch.”

The writer recently encountered a rather curious difficulty in connection with obtaining a free by-pass. The return pipe from the by-pass led into the case carrying the gearwheels of the camshaft and magneto drive, and oil continually flooded out from the end of the camshaft and other bearings. The waste and mess were sufficiently serious to warrant investigation, and the cover plate over the gears was accordingly taken off. It was then noticed that the oil delivered to the gearwheel case had only two small holes by which to drain away to the crankcase. The flow from the by-pass was beyond the proper capacity of these holes, and so the whole gearwheel case became filled with oil under considerable pressure, quite possibly 2 or 3 pounds per square inch, and it was not surprising that oil exuded from the ends of the bearing. A few extra limber-holes, if one may borrow a nautical expression, were drilled through to the crankcase, and no further trouble was experienced.

(124) Plug Oil Holes When Painting.

When the chassis of the car is repainted it is well to see that all exposed oil holes are stuffed with waste to prevent them from being choked. Failure to observe this precaution may result in the holes being clogged with paint, which if not removed before the car is started, will prevent oil reaching the bearings.

(125) Oiling the Magneto.

Never oil the circuit breaker or circuit breaker mechanism, unless for a drop of sperm oil that may be applied to the cam roller by means of a toothpick. If oil gets on the circuit breaker contact points, it will cause them to spark badly, resulting in pitting or destruction of the points. If the oil is occasionally applied to the cam roller or should oil accumulate on breaker points, the breaker should be rinsed out with gasoline to remove the surplus.

Pitted or carbonized contact points are capable of causing much trouble, and gummy oil or dirt will develop this trouble quicker than any other cause. Use only the best grade of thin sperm oil on the ball bearings.

In the course of time the circuit breaker contact points will wear or burn, causing imperfect contact, and too great a separation between the points. The contacts should be examined from time to time, and if rough or pitted, should be dressed down to a flat even bearing by means of a dead smooth file, and the distance readjusted. The contacts should not bear on a corner or edge, but should bear evenly over their entire surface to insure a maximum primary current and spark.