Introduction
LUBRICATION
The thousands of parts that go to make up the complete automobile are either fastened tightly to one or more other parts or they move against other parts. If they move against other parts they require lubrication in order to keep wear at a minimum, to provide for smooth and even move ment of the parts and to keep out water and dirt. In some places, as in the engine, rubbing speeds are high and pressures are great so that without proper lubrication there would be so much fric tion that heat would melt some of the parts, expand metals, close up clearances and cause the parts to stick.
Moving parts operate under a great variety of conditions including heat, cold, low or high speed, heavy or light loads, exposure to water, sand, dirt, air and other things that would tend to cause rust,
corrosion, expansion, shrinkage, and wear.
To secure the best lubrication, these various moving parts req ire a variety of types of lubri cants such as engine oils, gear lubricants and greases, each of which is available in a variety of light and heavy grades and with other varying characteristics to make them suitable each for a particular need.
Practically all lubricants are made from petro leum and are therefore called petroleum products. While petroleum in some form or other forms the main body of most lubricants, other chemicals, substances or soaps are added to provide required qualities that the petroleum itself does not possess.
Petroleum is a dark colored, slightly greenish liquid that comes from the ground. It does not mix with water and will burn when ignited. It becomes thicker when cold and thins out when heated. It has many other natural characteristics of which these are the principal ones.
Petroleum is a mixture of thousands of different chemical compounds, all made up of hydrogen and carbon and usually some impurities such as slight amounts of sulfur and other substances. Petroleum is called a hydrocarbon because its basic ingredients arc carbon and hydrogen. Thou sands of its different compounds have been sepa rated or isolated or combined in various ways and uses found for them. Apparently only the surface has been scratched because research laboratories are discovering more and more new compounds all the time and finding uses for many of them.
ENGINE OILS
Modern engine oils are designed as carefully as any engine part. The requirements of the engine are carefully measured under a wide variety of operating conditions. The oil designer can then determine the qualities wihch must be built into the motor oil.
Modern engines are built with extremely small clearances, and their precision parts are much more sensitive to rust, corrosion and the presence of deposits than older types of engines. Oils for the modern engine must be able to prevent such deposits from occurring.
By-products of incomplete combustion are the primary source of the substances which cause corrosion and other engine deposits. When gaso line is burned in an engine, more than a gallon of water is formed for each gallon of fuel burned. Although most of the water is in a gaseous form and goes out the exhaust pipe, some condenses on the cylinder walls (especially in cold weather, before the engine has warmed up) and escapes past the piston rings and is trapped in the crank case. Other corrosive combustion gases also escape past the piston rings and are condensed or dissolved in the oil. The life of almost every engine part depends on the ability of the oil to neutralize the effect of such corrosive substances. To provide this protection, oil-soluble chemical compounds are added to the oil during manu facture.
Under ideal conditions, gasoline burns (in the presence of an adequate supply of air) to form carbon dioxide and water. For a variety of rea sons, a gasoline engine cannot burn all the fuel completely. Some of the partially burned gasoline is converted into soot or carbon. The black smoke emitted from the exhaust when the gasoline-air mixture is extremely rich in gasoline is largely soot. Some of this soot and partially burned fuel escapes past the rings and is picked up in the oil. Such materials together with water tend to form sludge and varnish deposits on critical engine parts. If sludge is allowed to build up, oil pas sages may become restricted or clogged, resulting in insufficient oil flow to engine parts and rapid failure of these parts.
Some of the additives used in modern motor oils help the oil to resist thinning when hot or thickening when cold, help form lubricating films strong enough to withstand the extreme pressures found in some parts of the engine, and prevent entrapped air from foaming. Others serve as dis persing agents to keep sludge and varnish-forming products of combustion suspended in so fine a form that they do not cause damage or deposits. Still others help prevent rusting and corrosion by neutralizing acids and/or retard the deterioration (oxidation) of the oil which takes place at abnor mally high temperatures.
As the engine is operated, the level of contami nants in the oil is constantly increased, since combustion products arc continually being formed and picked up by the oil. This increasing level of contaminants makes it more and more difficult for the oil to protect and lubricate the engine.
For example, the additives which disperse the sludge-forming materials and prevent rust and corrosion are used up in performing their func tion. When this occurs, the oil can no longer do its job effectively. It must then be drained and re placed with a fresh supply.
This explains the commonly heard statement that oil does not wear out. Strictly speaking, that is perfectly true. The base oil does not wear out. But the additives which are essential to the proper functioning of the oil do become depleted, and it is not practical, in the field, to clean the oil and replenish the additives.
A properly serviced air cleaner is a big help in preventing most of the road dirt from reaching the oil, and periodic oil filter changes help keep the larger solid contaminants from circulating with the oil and causing wear. But neither of these two accessories is the complete answer to keeping the oil eompletely effective indefinitely. The engine crankcase must be drained regularly to remove the accumulations of contaminants and refilled with clean new oil.
The rate of contamination depends to a large extent on the kind of driving conditions under which the engine is operated. The more severe the conditions, the more frequently the oil should be
changed. However, it is impractical for the indi vidual driver to determine when the contaminant level is too high.
To overcome this problem, each automobile
manufacturer recommends oil change intervals for his cars, but these recommendations change from year to year, because of changes in engine design and construction, and vary from manufacturer to manufacturer. Some recommend different inter vals for different kinds of driving conditions. While this makes sense, it is difficult for the average motorist to remember. Therefore, the American Petroleum Institute (API) has come up with a universal recommendation: Change oil at least every three months or 3,000 miles, whichever comes first. But never exceed the car maker’s warranty requirements for oil change.
What A Motor Oil Must Do
It must:
1. Permit starting and circulate promptly.
2. Lubricate and prevent wear.
3. Reduce friction.
4. Protect against rust and corrosion.
5. Keep engine interior parts clean.
6. Cool engine parts.
7. Seal combustion pressures.
8. Be non-foaming.
These requirements are simple to state but changes in engine design and in driving condi tions have made them increasingly difficult to attain. The following sections describe in some detail how these requirements are met.
Oil Permits Starting
The relative ease with which an engine may be cranked and started depends not only on the condition of the battery, ignition system, proper fuel volatility and mixture ratio, but also on the motor oil. If the oil is too viscous or heavy at starting temperatures, it will impose such a drag on the moving parts that the engine cannot be cranked fast enough to start promptly and keep on running. This is especially true of modern high compression engines which require more power to crank.
Cold thickens all oils. So an oil for winter use must be thin enough to allow the battery and starter motor to crank the engine properly at the lowest temperature at which it will be used. In addition, the oil must be fluid enough to flow to the bearings the instant the engine starts in order to reduce wear. But it must also be thick enough to provide adequate prote ction w hen the engine
reaches normal operatin g temper atures.
The ch aracteristic of oil which determines the ease of cranking is its viscosity. Viscosity is a measure of the resistance of oil to motion of How. This resistance, or fluid friction of the oil, keeps it from being squeezed out from between engine surfaces when they are moving under load or pressure. This resistance is due to the adhesive and cohesive forces of the oil molecules in the oil itself. But this same resistance to motion or How is responsible for the major amount of drag imposed on the starter during cranking. Therefore it is important to use oil having suitable viscosity characteristics to insure satisf actory cranking, proper oil circulation and high temperature pro tection.
The Society of Automotive Engineers ( SAE) has established a viscosity-ran ge classification sys tem for crankcase lubricating oils which is used world-wide. All motor oils are classified according to this system and each is assigned as SAE num ber or numbers signifying the viscosity range or ranges into which each falls. The numbers in use today are SAE 5W, lOW, 20W, 20, 30, 40 and 50. Thick, slow-flowing oils have high numbers and thin oils have low numbers. The “W” denotes oils that are suitable for winter service under specific temperature conditions from the freezing point and below. To make sure that oils classified with the “W” have proper flow characteristics at low temperatures, their viscosities are determined at 0° F. SAE numbered oils which do not include the “W” have their viscosities measure d at 210° F. to be certain that they have adequat e viscosity.
Because the effect of tempera ture changes upon viscosity varies widely with diff erent types of oil, a standard of measurement of th e amount of vis cosity change with the change of temperature has been established and is known as Viscosity Index (V.I.)_. A high viscosity index oil is one that shows a relatively small change in vis cosity over a wide range of temperature s.
Today, through the selective choice of crude oil base stocks, newer refining methods, and the addi tion of special chemicals, there are many high viscosity index oils that are light enough for easy cranking at low temperatures and heavy enough to perform satisfactorily at high temperatur es. These oils will meet the viscosity requirem ents and do the work of two or more SAE grades and are labelled SAE 5W-20, SAE 5W-30, SAE 10W- 20W-30, SAE lOW-30, SAE lOW-40 and SAE 20W-40.
These are known as all-season or all-weather oils, as well as multi-viscosity grade, multi-grade, or multi-viscosity oils. The term “multi-viscosity” is a misnomer because oils vary in viscosity with temperatures, whether single or multi SAE grade. Multi-grade (as well as single grade) oils are recommended by all car manufacturers.
There is not complete agreement between car manufacturers in regard to SAE grade recom mendations for different temperature conditions and oil companies set limits for their own oils. To avoid starting problems due to use of the wrong SAE grade, car owners should change, before cold weather, to the SAE grade which is suitable for the lowest temperature to be expected wherever the car may be used.
If specilic information is not available, the fol lowing is a composite of car manufacturer and oil company advice:
” SAE 5W single grade oils should not be used for sus tained high speed driving (above 60 mph).
Oil Distribution
Once an engine is started, the oil must circulate promptly and lubricate all moving surfaces to prevent harmful metal-to-metal contact and con sequent wear, scoring or seizure of engine parts. Oil films on bearings and cylinder walls are dis placed rather quickly with movement and pres sure. Therefore these oil films must be replenished by adequate flow and proper distribution of oil through the lubrication system.
Prompt oil circulation at low temperatures freezing and below-is dependent on the pour point and viscosity of the oil at the lowest tem perature to be expected.
The pour point of an oil is the lowest temperature at which the oil will just flow or pour under the force of gravity. Normally, the pour point of an oil has little or nothing to do with the ease of cranking. If the pour point of the oil is not several degrees lower than the starting temperature, how ever, prompt oil circulation cannot be achieved.
The viscosity of the oil must be low enough at the starting temperature for the engine to be cranked rapidly enough to enable the engine to start. Once the engine starts, however the viscosity of the oil must be high enough at top operating temperatures to assure adequate protection of the working parts.
Oil Must Lubricate and Prevent Wear
The most important function of the oil is to lubricate and prevent wear of moving surfaces. In many parts of the engine the oil can establish a complete unbroken oil film between the surfaces, which is constantly replenished. This is known as full film lubrication, or hydrodynamic lubrication.
Full film lubrication occurs when the working surfaces are in motion and are completely sepa rated by a relatively thick oil film. The most important quality of the oil in keeping parts sepa rated is its viscosity at the temperature existing. The viscosity must remain high enough to main tain complete metal-to-metal separation. Since the metals do not make contact in full film lubrication, wear cannot occur unless a solid particle large enough to exceed the thickness of the oil film causes abrasion or scratching of the moving sur faces. The crankshaft bearings, the connecting rods, camshaft and piston pins normally operate under full film conditions.
Under some conditions, it is impossible to estab lish a complete oil film between the moving parts and there is more or less intermittent metal-to metal contact between the high spots on the slid ing surfaces. This is called boundary lubrication, where the load is only partly supported by the oil film. Boundary conditions always exist during starting and stopping of the engine and during the break-in period of a new or reconditioned engine, when surfaces are relatively rough and irregular. Boundary lubrication conditions also exist in the area of the top piston ring because the oil supply is limited and temperatures are relatively high.
On some engine parts, the loads are high enough to squeeze out or to rupture the oil film and to permit appreciable m tal-to-metal contact. When this occurs, the friction generated between the surfaces produces sufficient heat to cause one or both of the metals in contact to melt and to weld to the other. This results either in immediate seizure, or in the surfaces being torn apart and roughened, which progressively worsens the situation.
Extreme pressure conditions can develop from lack of lubrication, inadequate clearance, extreme heat, heavily loaded parts, and sometimes from the use of the wrong type or grade of oil for the operating conditions. In modern engines, the valve operating system, cams, valve lifters, push rods, valve stem tips and parts of the rocker arms operate under extreme pressure conditions be cause they carry heavy loads on very small contact areas. The unit loading may be very high, up to as much as 200,000 psi. This is many times greater than loads on the connecting rod bearings or piston pins.
Modern oils contain additives which react with the metals to form surface coatings that are highly adhesive. These coatings reduce the friction be tween the metals and prevent welding.
Oil Reduces Friction
Where full film lubrication is present, no metal to-metal friction exists. Neverth eless, force is re quired to move the parts relative to one another. This is the force necessary to overcome the viscos ity effect of the lubricant. The viscosity must be high enough to maintain an unbroken film but should not be greater than necessary, since this will increase the force necessary to overcome it. This is the reason manufacturers specify the recommended viscosity by indicating the SAE number of the oil to be used at various atmos pheric temperatures. It is an attempt to be cer tain that the lubricant will have adequate but not excessive viscosity at normal operating tempera tures. When an oil becomes contaminated with solids (soot, dirt, etc.) or with sludge, the viscos ity is increased and the engine becomes less effi cient-that is, it must generate more power and burn more fuel to do the same amount of work. Contaminant levels in the oil must be kept low for this reason, and this can be accomplished only by regular drain intervals.
Metal-to-metal contact does occur during boundary and extreme pressure lubrication condi tions which appear in various parts of the engine. The viscosity of the oil has only a small effect on reducing friction under these conditions. How ever, the amount and type of chemical additives blended into the oil during manufacture do have a very marked beneficial effect on reducing friction in these circumstances.
Oil Can Keep Engine Interiors Clean
It was pointed out earlier that modern oils can prevent dangerous accumulations of sludge and varnish on engine parts and in the crankcas e, tim ing gear covers and valve covers. The basic objec tive here is not simply to maintain the en gine in a clean condition, but to prevent such deposits of sludge and varnish from interfering with the proper operation of the engine.
The varnish and sludge-forming m aterials do little or no harm in the oil but they may accumu late to too high a level and/or clump together to form large masses which can restrict flow to vari ous parts of the engine. Or they can combin e with oxygen from the air and be baked by engine heat to a sticky or hard binder which keeps the engine parts from moving freely. What we see as sludge in the engine is merely large amounts of such materials clumped together to form a large vis cous mass. The water vapor which condenses in the crankcase in cold engine operation aggravates this condition. Therefore it can be seen that sludge formation is generally a problem of low engine temperature operation. The materials which form sludge are a combination of water from condensation, dirt and products of oil de terioration and incomplete combustion. The rate at which these materials accumulate in the crank case oil is related to factors of engine operation. Rich mixtures which occur on starting or from a sticking choke, restricted air cleaner, or poor igni tion, increase the rate.
Straight mineral oils have only a limited ability to keep these sludge-forming materials from clumping and forming a large mass of sludge in the interior of the engine. Modern oils have chemical additives known as detergent/ dispers ants blended into them during manufacture. These work mainly by keeping the sludge-forming materials from clumping together . In other words, the sludge-forming materials are dispersed in tiny particles throughout the oil and kept suspended in such form that they cannot settle out on engine parts.
The sludge-forming materials are so small in size when first formed that they cannot be seen even with a high powered optical microscope. In such form and size even the finest oil filters re move them and they are much smaller than the thickness of the oil film on engine parts. There fore, they will not cause wear or damage as long as they remain in a small size and are well dis persed. The function of the detergent/dispersant in a modern oil is to suspend these contaminants in suc;h fine form within the oil so that they can be removed when the oil is drained.
In service the detergent/dispersant is used up doing its job of suspending contaminants. While in theory, more detergent/dispe rsant could be added to a used oil after the original additive is exhausted, this is not practical or economical in practice.
By contrast with sludge formation, the varnish forming materials react differently in an engine. These materials combine with oxygen from the air in the crankcase. At first the resulting compounds arc only slightly more viscous than the oil but they continue to react with the oxygen and themselves, and are baked by engine heat into a hard, tena cious coating on the hotter parts of the engine.
The compression rings and pistons are particularly sensitive to varnish deposits, and if allowed to accumulate, the piston rings may become frozen or stuck in their grooves. They can no longer per form their jobs efficiently and vehicle operation suffers.
Detergent / dispersants are very effective in pre venting varnish deposits. Because the materials are dispersed in the oil rather than being allowed to come in contact with one another, the chemical reaction of combining together is prevented. Be cause this is fundamentally a process which de pends on oxidation, the detergent also works by interrupting this oxidation process. Certain of the additives used to prevent corrosion also prevent the oxidation process from occurring.
As these additives are used up, the oil becomes less and less effective in preventing sludge and varnish deposits, and should be replaced.
Deter gent/ dispersants used in motor oil have only a very limited ability to clean up deposits of sludge and varnish already formed in an engine. Once formed, sludge and varnish can only really be removed during mechanical overhaul. The function of a detergent/ dispersant in a modern oil is to prevent the formation of sludge and varnish, not to remove such deposits after they have formed.
Modern engines cannot tolerate excessive amounts of sludge and varnish. So-called non detergent motor oils (mineral oils without addi tives) do not provide a modern engine with ade quate protection against the accumulation of sludge and varnish and do not contain the neces sary chemical to prevent damage to the engine’s valve operating mechanisms. Detergent /dispers ant type oils for modern engines are recom mended today by all U.S. and foreign car manufacturers.
Combustion Chamber Deposits
All engines must allow some oil to reach the area of the top piston ring in order to lubricate both the rings and cylinder walls. This oil is then exposed to the heat and flame of the burning fuel. Part of this oil then actually bums off. Modern oils bum cleanly under these conditions, leaving little or no residue (carbon). Detergent/ dispersants keep the piston rings free in their grooves in order to minimize the amount of oil that reaches the combustion chamber. This not only reduces oil consumption, but more importantly, keeps the amount of combustion chamber deposits at a minimum.
Some deposits in the combustion chamber are unavoidable, since they result from incomplete combustion of the fuel. However, a modem oil can minimize such deposits by keeping rings oper ating freely, keeping combustion pressures high and promoting more complete combustion of the fuel.
Excessive combustion chamber deposits ad versely effect engine operation. They may deposit on the spark plugs causing them to short out, cause pinging or knock and other combustion irregularities , and generally cause loss of efficiency and economy of operation. Because they act as heat barriers, pistons, rings, spark plugs and valves are not properly cooled and are damaged or actually fail.
The function of a motor oil in preventing exces sive combustion chamber deposits is limited to two areas:
1. That portion of the oil which reaches the combustion chamber should bum cleanly.
2. The oil must keep the rings free to do their job of minimizing the amount of oil which reaches the combustion chamber.
Motor oil is often blamed for excessive combus tion chamber deposits. However, it is worth re membering that if an engine is not using an excessive amount of oil, the oil cannot cause ex cessive deposits.
Multi-grade oils (SAE SW-20, SW-30, lOW-30, lOW-40 and 20W-40) are manufactured from lubricating oil stocks which bum cleanly and con tain additives which leave little or no deposits in the combustion chamber.
Oil Cools Engine Parts
Water is usually considered to be the sole cool ing agent in an automobile engine. Actually, only abou t 60% of the cooling job is done by the water, and only the upper part of the engine is so cooled. Water cools the cylinder walls, the cylinder heads and valves, but the crankshaft, main and connect ing rod bearings, the camshaft and its bearings, th e timing gears, the pistons and many other parts in the lower section of the engine depend almost entirely on lubricating oil for necessary cooling. All of these parts have definite temperature limits which must not be exceeded or failure will result. Some parts can tolerate fairly high temperatures, but others, such as the main and connecting rod bearings , must run relatively cool or they will fail rapidly during operation.
These parts must be supplied with plenty of cool oil, which picks up the heat and carries it to the crankcase where it is eje cted to the surround ing air. Some idea of the temperatures involved may help in understanding this important func tion of a motor oil.
Combustion temperatures are 2000° to 3000°·F.
Certain parts of the valves may be at tempera tures of 1000° to 1200° F. Pistons sometimes reach 1000° F. and this heat is conducted down the connecting rod to the rod bearings. Tin and lead, which are common metals used in bearings, become very soft at around 350° F. and melt at 450° and 620° F. respectively. After warm up, crankcase oil temperatures may reach 180°-225°
F. and oil is supplied to the bearings at these temperatures. At the bearing, the oil picks up heat and in many engines leaves the bearing at tem peratures of about 225° to 250° F. This keeps the bearing from exceeding these safe temperatures. The hot oil then drains back to the crankcase and splashes onto the bottom and sides where heat is removed and carried away by the surrounding air.
To keep this cooling process going, large vol umes of oil must be constantly circulated to bear ings and other engine parts. If the supply of oil is interrupted, parts heat up rapidly both as a result of increased friction and from combustion tem peratures.
While only a small quantity of oil is needed at any one time to provide lubrication, the oil pump must circulate many gallons of oil per minute to provide cooling of engine parts. Chemical addi tives and the physical properties of the oil have little effect on its power to provide cooling. The secret is to get large quantities of oil constantly circulating through the engine and over hot en gine parts. The engine designer has provided for this with large capacity oil pumps, and lines and oil passages large enough to handle the volume of oil necessary.
However, if these oil lines or passages become partially or completely plugged with deposits, oil does not circulate properly, the vital job of cooling engine parts may not be done and early failure may result. This is another reason for changing oil before the contaminant level becomes too high. The level of oil in the crankcase must be main tained and should never indicate more than one quart low on the dipstick in order to be certain that sufficient volume of oil is pres ent in the engine to provide for proper cooling.
Oil Seals in Combustion Pressures
The surfaces of the piston rings, ring grooves and cylinder walls are not complet ely smooth. If examined under a microscope, these surfaces consist of minute hills and valleys. The rings therefore cannot completely prevent high compression and combustion pressures from escaping into the low pressure area of the crankcase. This costs power and reduces efficiency. The motor oil fills in these hills and valleys on ring and cylinder wall surfaces and helps seal compression and combustion pres sures. Because the oil film at these points is rather thin-generally less than .001″ thick-the oil can not compensate for excessive wear of rings, grooves and cylinder walls.
Oil Must Be Non-Foaming
Foam is simply a lot of air bubbles in an oil, which do not collapse readily. Becau se of the many rapidly moving engine pa rts, air in the crankcase is constantly being whipped into the oil. These air bubbles normally float t o the surface and break or collapse. However , wat er and certain other contaminants slow up the rate at which such air bubbles collapse and large amounts of foam are the result.
Modern oils contain a small amount of a chemi cal additive called a foam inhibitor, which speeds up the foam collapse and causes air bubbles to break almost as soon as they are formed .
Foam is a poor heat conductor, so engine cool ing is impaired if the amount of foam is excessive. Foam does not have much ability to carry the load and prevent wear in hydraulic valve lifters and bearings, since air is easily compressible. Oil on the other hand is virtually incompressible.
Oil Classification
The SAE classification system mentioned earlier only identifies viscosity and does not indicat e anything about the type of the oil, its quality or the service for which it is intended. So a system of classification has been developed for the API by a joint industry committee composed of representa tives of engine builders and oil companies. Letter designations are used which indicate the kind and type of service for which the oil is suitable. Both gasoline and diesel engine oils are so classified, although aviation oils are not included. All the factors which affect oil and engine performance have been considered, including engine design, fuel characteristics, operating conditions, the type of lubricating oil, and maintenance. There are two classifications for gasoline engine oils and three for diesel engine oils. The gasoline en gine oil classifications are:
Service MS. This represents the most severe service for modern gasoline engines which have deposit, wear and corrosion control problems, and which operate at extremely high or low tempera tures, including stop-and-go service, short trip operation, or which experience long periods of idling. Also, it includes high speed expressway operation.
This classification demands the highest quality in a motor oil. Because of the service conditions under which such oils must produce satisfactory lubrication, these oils are compounded with a wide variety of additives, including detergent/ dispersants. Service MS oils meet all the require ments for engines operating under the car manu facturers’ warranty, including those equipped with emission control devices. Service MS oils are recommended for all cars and all driving con ditions.
Service MM. This represents a more moderate service requirement than Service MS. It includes moderate to high speeds, loads and temperatures. These engines generally have deposit and bearing corrosion control problems when crankcase oil temperatures are high. This classification defines oils which are inhibited against oxidation and bearing corrosion but contain less detergent/ dis persant additive than oils for Service MS.
Service MM oils give reasonable performance in moderate service in non-critical engines such as in older model cars, but are neither suitable nor recommended if stop-and-go, idling or short trip operation is involved. Oils of this classification are not recommended for modern engines operating under manufacturers’ warranty.
In addition to the above service classifications, there was originally a Service ML classification, but this was discontinued in May, 1969. Oil for Service ML is not recommended for use in pas senger car engines, although it is recommended ‘ by the manufacturers of some two-cycle engines and some older model farm tractors.
FRICTION
Friction is the resistance set up between two surfaces that move against each other. In the automobile there is some friction between parts due to the load or weight of one part against another as in the wheel bearings which carry the load of the car and the body to the wheels. If the wheels operated without lubrication and without ball or roller bearings the friction would be so great that the parts would heat up, shred the metal and eventually either destroy the bearings or melt the metal.
The pistons move up and down in the cylinders, often at speeds in excess of 40 mph. Without a lubricant to separate the metal surfaces the fric tion would generate enough heat to melt the metal pistons, rings, cylinders and other parts. This situation is further complicated by the fact that the piston rings press strongly against the cylinder walls as they expand outward. Furthermore, there is considerable side pressure of the rings and pistons against the cylinder walls when the con necting rod is at an angle or is off dead center. This is caused either by the pressure of the explo sion against the top of the piston or to a lesser extent to the drag of the rod on the intake stroke followed by side pressure on the compression stroke.
There is friction between the cams and the valve lifters, both at the rubbing points between the cams and the lifters and the side pressure of the valve lifters against the guides. There is fric tion between the gear teeth of the timing gears of the engine, at all the main and connecting rod bearings, the water pump shaft, the oil pump, the distributor shaft, rotating parts of the transmission no matter of what type, the rear axle gears, uni versal joints and in fact every moving part on the entire car.
At some of these points the pressure is ex tremely heavy as between the teeth of the hypoid rear axle gears where pressure may run up to many tons during periods of fast driving, hill climbing or pulling through soft sand or mud in lower transmission gears.
Friction cannot be eliminated but it can be greatly reduced by the usc of lubricants.
Lubrication of the various parts is accomplished in a number of different ways.
HOW ENGINE IS LUBRICATED
The engine is lubricated from the oil in the an, Figs. 1 to 4. This oil is circulated to the vanous parts by a pump that is located in the lower part of the engine, or sometimes in the front cover.
The oil, some 4 to 6 quarts, is picked up by the oil pump after being drawn through a screen which is intended to prevent the passage of larger pieces of dirt. From the oil pump, the oil is forced under pr essure to the crankshaft main bearings and the camshaft bearings.
Oil is distributed evenly over the surfaces of the crankshaft main bearings by grooves in the bear ings. A portion of this oil is forced into holes in the crankshaft which carry a supply to each connect ing rod bearing. The oil that is thrown off the connecting rods is splashed onto the lower p arts of the cylinder walls, from wher e it is carried up and distributed around the entire cylinder wall. Some is also splashed onto the underside of the pistons, where it perform s two f unctions-cooling the pistons and lubricating the piston pins. The surplus from the cylinder walls, m ain bearings and connecting rod bearings is splashed over the camshaft, valve lifters, gears and any other in ternal working parts.
Hydraulic valve lifters are lubricated by a direct pressure line at the same time as te amsha t bearings. This oil, from the hyd r aulic hfters , IS also used sometimes to lubricate the overhead valve gear through hollow push rods. In other engines, there is an oil pipe that carries oil to the valve rocker arm shaft and to other parts that need oil.The oil line is connected to a mech anism which
carries the pressure indication to th e oil gau ge or indicator lamp on the instrum ent p an el. This mechanism can be mechanical or electrical.
All modern cars have a full flow oil filter in th e engine lubrication system. It is connected into th e system right after the oil pump and before the crankshaft main bearings, so that all oil is filtered before going to any bearings.
OIL LEAKAGE PREVENTIVES
Oil is prevented from leaking out of th e engine in several ways. The front and rear main bea rings are provided with oil seals. At the rear bearing, there is an oil slinger which is simply a disc on the crankshaft. This being of great er diameter than the shaft, throws off any oil that creeps along th e shaft and drains down into the pan. In addition there is a main bearing seal which prevents oil from oozing out along th e shaft. As lon g as the seals are in good condition and in place, there should be little or no oil leakage from the shaft ends. If th e bearing is badly worn or if the seal leaks or is out of position , th ere may be consider able leakage of oil, usu ally at th e rear end and this may get into the clutch hou sing or leak out onto the ground depending on the design of the par ts.
ENGINE OIL PAN
The en gine oil pan which holds the engine oil supply of a bout 4 to 6 qu arts is held to the crankcase by a numb er of cap screws or bolts and a gasket , usu ally cork, is pl aced between the pan and th e crankcas e so that wh en the cap screws or bolts are snugged up, th ere will be an oil-tight joint. Und er conditions of normal use, time and for other r easons, these screws may loosen and may require ti ghtening to keep oil from leaking out along th e gasket.
The only other openin gs in th e crankcase are the crankcase drain plu g which is usually to the rear of th e oil pan and the filler pipe which is at the side, th e front or the top of th e engine. The oil dipstick or level gauge is always on the same side or n ear the oil filler pipe so that the oil level can be checked and refilled from the same spot.
OIL FILLER
Mod ern engines are filled with oil through a filler on top of th e engine, and nearly all have a cap which seals the opening. Older engines have an oil filler pipe which extend s from the crank case. This is closed with a filler cap so constructed as to prevent rain or splashed water from enter ing. The filler cap often contains an air cleaner mad e of meta l wool and a strainer to keep out dust and dirt. This is necessary beca use in the course of heating and cooling the crankcase breathes air in and out. In addition, the ventilat ing arrangem ent draws its air into the crank case through this cap.
Other ventilating arrangements on older en gines include the provision of an opening toward the rear of the engine with a scoop which pu lls the air out of the crankcase. Some engines also used to have an intake scoop through which fresh air was blown by the fan and by the forward motion of the car. These openings were usually provided with elementary air cleaners, which needed to be cleaned and serviced from time to time, Fig. 5.
ENGINE OIL CONTAMINANTS
The greatest source of engine oil contamina tion comes from unburned liquid fuel which may pass by th e piston rings from the combustion chamber. To this liquid fuel may also be added water that is condensed from the process of combustion and harmful and corrosive chemicals which are also form ed during the process of combustion.
Many of the oil contaminants, as they are called , form easily when the engine is cold. If the engine is run long enough at full operating tem perature, they can be evaporated and may be drawn off through the ventilating system.
Water vapor is one of the products of combus tion. That is, it is chemically necessary to form some water in the form of vapor in order for the oxygen of the air to combine with the carbon in the gasoline. The hydrogen that is released com bines with the oxygen of the air to form water. If some is present this combines with some of the oxygen and hydrogen to form one of the acids, sulfuric or sulfurous. Either one is corrosive.
With the cold engine, the water vapor, acidvapor and some of the fuel vapor condense on the cold cylinder walls. Whenever the cylinder walls are colder than about 140 deg., condensation will take place just as it does on the outside of a glass of water or on the bathroom window or mirror when you take a warm shower and release water vapor which condenses onto anything cooler.
This condensed water and fuel are carried down past the piston rings and into the crankcase where, being heavier than oil, they sink to the bottom. Later they may form an emulsion of the consistency of mayonnaise, may combine with dirt or worn metal or carbon particles or, if the crank case remains hot enough, they may reduce by evaporation or may be strained out by the· oil filter.
The condensed water does not mix with the oil but forms sludge, paste or other material which is neither solid nor liquid and which often clogs up oil passages, oil screens, and in severe cases, occu pies considerable bulk in the crankcase. This is always liable to cause trouble.
The fuel that works down into the crankcase will mix with the oil and it tends to thin it out or dilute it. This not only reduces the carrying capac ity of the oil and the lubrication value but it also tends to deposit inside the engine and to leak out. When the engine has run long enough to warm up, this condensed fuel evaporates and is carried out through the ventilating system. However, it takes time and mileage to bring the oil up to full operating temperature and to keep it there. The amount of water and fuel that is condensed in a few minutes on a cold day may take hours of engine runnin g to work off .
Much, if no t all, of the f uel that is condensed in the f ew seconds or minutes of starting comes from the use of th e choke. It is not possible to start an automobile engine cold with th e same mixture as that which it later run s on when heated up. Further, the fuel itself is m ore difficult to evapo rate when cold so th e mixture has to be made extremely heavy with the choke. If of the auto matic type, the choke will usually be set a little on the rich side to make sure of a start. As the engine heats up, the automatic choke releases and gradu ally returns mixture to its proper value.
If the choke is of the hand-operated type, there is almost always a tendency for the driver to over choke, to keep the mixture too rich till the engine warms up and then, m ost unfortunately of all, many times the driver forgets all about the choke and drives merrily along with a stream of black smoke coming out of the exhaust and with unseen harm being done to th e inside of the engine in the form of oil dilution and carbon formation from the over-rich mixture. Not only this, but the soot mixes with the oil and in time this becomes abra sive and causes wear.
In order for the lubricating oil to perform the way it is planned, it is necsseary that the proper grade or body of oil be used for the temperatures and that the entire cooling system of th e engine be maintained so that it operates at th e proper tem perature. The oil level must be maintained be tween certain limits, not too much and not too little. If some of the inside p arts of the engine wear too much and open up th e clearances, too much oil will be used and where oil passages are allowed to clog up, t oo little oil may pass. If the level gets too low, the oil may overheat under excessive load conditions and if it is carried too high, too much will be thrown on the cylinder walls as a result of which carbon will form rapidly in the cylinder heads and aroun d the valves, the spark plugs will become fouled and other opera tional difficulties will be likely to occur.