Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
THE LUBRICATION SYSTEM
Lubrication is the action of applying a substance such as oil or grease to an engine or component so as to
minimize friction and allow smooth movement.
PURPOSE OF LUBRICATION
a) To reduce the friction between moving parts
b) To increase the efficiency
c) To minimize the vibrations
d) To reduce the corrosion and carbon deposits
e) To reduce the heat of moving parts
f) To minimize power loss due to friction
g) To reduce the noise created by moving parts
h) To provide cooling to the engine
PROPERTIES OF LUBRICATING OIL
-The quality of a lubricating oil is tested for the following various properties to evaluate its suitability and
merits for certain service conditions.
(a) Viscosity
-It is the ability of the oil to resist internal deformation due to mechanical stresses and hence it is a
measure of the ability of the oil film to carry a load.
-Viscosity is a measure of the flow ability of oil under a particular temperature and pressure.
- A more viscous oil can carry a greater load, but it will offer greater friction to sliding movement of the
one bearing surface over the other.
-Viscosity of oil decreases with increase in temperature.
(b) Flash Point or Fire Point
-The lowest temperatures at which the oil flashes and fires (burns continuously), known as flash and fire
points.
-These two temperatures must be sufficiently high for any lubricating oil to avoid flash or burn during
use.
(c) Cloud
-The low temperature at which the lubricant changes from liquid state to a plastic or solid state is called
cloud point.
-In some cases the oil appears to be cloudy at the start of solidification.
(d) Carbon Residue
-Lubricating oils being the chemical compounds of carbon and hydrogen, when burnt it deposit carbon on
the engine parts.
-This should be as low as possible for lubricating oil.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
(e) Corrosion
-A lubricant should not corrode the working parts of an engine and it must retain its properties even in the
presence of foreign matter and additives.
(f) Pour Point
-The lowest temperature at which the oil pours (Flow by gravity) is called its pour point.
-Below this temperature the oil becomes plastic, so it does not produce hydrodynamic lubrication and
therefore cannot be used below this temperature.
-It is an indication of its ability to move at low temperatures.
-This property must be considered because of its effect on starting an engine in cold weather and on free
circulation of oil through exterior feed pipes when pressure is not applied.
(g) Color
-This test is not so important except for checking the uniformity of any given grade of oil.
(h) Emulsification
-A lubricant when mixed with water tends to separate.
-The emulsification number is an index of the tendency of any oil to emulsify with water.
(i) Oxidation at High Temperature
-Lubricating oils may break down at high temperature due to oxidation producing hard carbon and
varnish, which deposits on the engine parts.
-Therefore, lubricants must resist oxidation.
(j) Evaporation
-Evaporation test is conducted to find the quantity of oil that may evaporate at high temperatures.
-Lubricating oil should have a low evaporation characteristic.
(kl)Sulphur Content
-Sulphur in a corrosive form is detrimental in lubricating oil.
-Thus its presence should be avoided.
(l) Specific Gravity
- It is a measure of density of oil.
-Specific gravity of lubricating oil varies considerably and hence should not be regarded as the main
indication of its lubricating property.
(m) Oiliness
- This is the property which enables oil to spread over and adhere to the surface of the bearing.
TYPES OF LUBRICANTS
- Most lubricants are oils or greases. However, in special circumstances other fluids like water, air etc.
and solids such as graphite may perform the function of lubrication.
-Synthetic lubricants are also used occasionally.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
(a) Synthetic Oil
-Most synthetic oils are made from a petroleum or crude oil base stock.
-The differences between most conventional oils and synthetic oils are in the refining process and the
additives used.
-Additives in the synthetic oils, which are usually more than that in conventional oils, are then blended
with the synthetic stock.
-Additional energy is used in the preparation of synthetic oils and hence these oils are more expensive
than conventional oils.
Advantages of synthetic oil
(i) Increased oil change intervals
(ii) Reduced wear in engine parts
(iii) Increased fuel economy because synthetic oil provides less friction.
(iv) Improved high-temperature protection of engine parts.
(v) Easier cold-weather starting because of reduced friction.
(b) Re-refined oil
-Re-refined oil is used engine oil that has been recycled.
-Engine oils made from recycled based stock can be equivalent in performance to those made from virgin
petroleum base stock, if proper quality control is given to the used oil base stock and the processing
procedure.
-The use of re-refined oil reduces pollution from the improper disposal of used oil.
-If other alternative fuels such as methanol or hydrogen are used in large numbers of cars, then oils with
more compatible characteristics with these fuels are to be developed.
Classification of Oil
-The lubricating oils are normally classified according to their viscosity.
-The SAE (Society of Automotive Engineers) method of assigning number to different oils is used
universally.
-SAE has assigned a number to an oil whose viscosity at given temperatures falls in certain range.
-There are two temperatures used as reference for assigning the number to oils – 18°C and 99°C.
-SAE, 5 W, 10 W, 20 W grades are defined in terms of viscosity at – 18°C and are the oils which render
starting of engine in cold weather easy.
-SAE, 20, 30, 40 and 50 grades are defined in terms of viscosity at 99°C; these oils work satisfactorily in
normal and hot climates.
-These numbers are merely used for classification of oil according to viscosity and do not indicate the
quality of oil since factors like stability, oiliness etc. are not considered.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
LUBLICATION OIL ADDITIVES
Additives are used in motor oils for three different reasons:
(a) To replace some properties removed during refining.
(b) To reinforce some of the oil's natural properties.
(c) To provide the oil with new properties it did not originally have.
TYPES OF OIL ADDITIVES
-Simple mineral oils have most of the required characteristics as a good lubricant.
-However, varying operating conditions require some specific properties which it cannot meet, as high
viscosity index and resistance to oxidation and corrosion.
- In order to achieve some required properties, different types of compounds, called additives are added.
(i) Pour-point Depressants
-The pour point of oil is the lowest temperature at which the oil pours or remains fluid.
-At extremely low temperature some oils become so thick that they do not pour at all.
-When this happens, excessive wear occurs on bearings, piston rings, and cylinders during initial
operation after the engine is started in cold weather.
-Certain additives are used in many engine oils to depress the pour point.
(ii) Oxidation Inhibitors
-When high-temperature oil is agitated, oxygen in the air combines with the oil, oxidizing some of the oil
into a sticky tar like substance and other corrosive compounds.
-The tar like substance can clog oil passages, which may cause some components to operate without
proper lubrication.
-The corrosive compounds may erode bearings prematurely. Therefore, oil oxidation is undesirable.
-Oxidation inhibitors are added to engine oils to assist the oil in resisting oxidation.
(iii) Corrosion and Rust Inhibitors
-Acids can form in the oil at high temperatures and cause corrosion of engine bearings.
-Corrosion inhibitors are added to the oil to prevent this corrosion.
-The rust inhibitors help to neutralize acids that get past the piston rings and collect in the oil.
(iv) Extreme Pressure Resistant
-Extreme pressure additives prevent the oil from being squeezed out of the bearing surfaces when
subjected to high pressures.
(v) Detergents and Dispersants
-Detergents are added to the oil to slow down the formation of carbon deposits.
-The detergent loosens the deposits of carbon or tar like material and then carries the
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
-Smaller particles are removed from the oil by the oil filter.
-Heavier particles drop to the bottom of the crankcase, and they are removed when the oil is changed.
(vi) Antifoaming Additives
-The rotating movement of the crankshaft and connecting rods may foam the oil in the crankcase.
-Excessive foaming of the oil destroys the normal hydrodynamic oil film on bearing surfaces and other
engine parts.
-Antifoaming additives prevent excessive oil foaming,
(vii) Friction Modifiers (Oiliness Agents)
-Some refiners add friction modifiers to their engine oil, which reduce the friction between the layers of
oil in the hydrodynamic oil film on bearing or other surfaces.
PRINCIPLES OF LUBRICATION
-Basically, lubrication is governed by two principles of lubrication: Hydrodynamic Lubrication,
Hydrostatic Lubrication and Boundary Lubrication.
Hydrodynamic Lubrication or Thick Film Lubrication
-Hydrodynamic lubrication is said to exist when the moving surfaces are separated by the pressure of a
continuous unbroken film or layer of lubrication.
-In this type of lubrication, the load is taken completely by the oil film.
-Hydrodynamic lubrication depends on the relative speed between the surfaces, oil viscosity, load, and
clearance between the moving or sliding surfaces.
-Example; used in the main bearings of a diesel engine.
Hydraulic Lubrication
-Hydrostatic lubrication is essentially a form of hydrodynamic lubrication in which the metal surfaces are
separated by a complete film of oil, but instead of being self-generated, the separating pressure is supplied
by an external oil pump.
-Hydrostatic lubrication depends on the inlet pressure of lube oil and clearance between the metal
surfaces, whereas in hydrodynamic lubrication it depends on the relative speed between the surfaces, oil
viscosity, load on the surfaces, and clearance between the moving surfaces.
-Example; Gudgeon pin bearing in two stroke engines employs this hydrostatic lubrication mechanism;
load is very high and the motion is not continuous as the bearing oscillation is fairly short. Thus,
hydrodynamic lubrication cannot be achieved.
Boundary Lubrication or Thin Film Lubrication
-Under the hydro-dynamic condition the oil film supports the load.
-If the oil film becomes thin enough so as not to support the load without occasional metal to metal
contact then journal friction developed is called boundary friction and the lubrication existing in this
range is known as boundary lubrication.
-Example; Piston rings and when cylinder liner is at TDC and BDC position when the piston direction
changes and if the relative speed is very slow.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
LUBRICATION SYSTEM
-Lubricating system is a mechanical system of lubricating internal combustion engines in which a pump
forces oil into the engine bearings.
The main parts of an engine which need lubrication are as given under:
(i) Main crankshaft bearings.
(ii) Big-end bearings.
(iii) Small end or gudgeon pin bearings.
(iv) Piston rings and cylinder walls.
(v) Timing gears.
(vi) Camshaft and camshaft bearings.
(vii) Valve mechanism.
(viii) Valve guides, valve tappets and rocker arms.
CLASSIFICATION OF LUBRICATING (OIL) SYSTEMS
-Various lubrication systems used for I.C. engines may be classified as:
1. Wet sump lubrication system.
2. Dry sump lubrication system.
1. Wet sump lubrication system
--In a wet sump, the oil that you put into the engine is stored beneath the crankshaft in the oil pan.
-This pan has to be large and deep enough.
-In a wet sump, the oil pump sucks oil from the bottom of the oil pan through a tube, and then pumps it to
the rest of the engine.
(i) Splash
-In the splash lubricating system, oil is splashed up from the oil pan by dippers/scoops on the connecting-
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
rod bearing caps with each crankshaft revolution.
-The oil is thrown upward as droplets or fine mist and provides adequate lubrication to valve mechanisms,
piston pins, cylinder walls, and piston rings.
-Surplus oil eventually flows back to the oil sump. Oil level in the troughs is maintained by means of a oil
pump which takes oil from sump
(ii) Combination Splash and Force Feed
-In a combination splash and force feed, oil is delivered to some parts by means of splashing and other
parts through oil passages under pressure from the oil pump.
-The oil from the pump enters the oil galleries.
-From the oil galleries, it flows to the main bearings and camshaft bearings.
-Cylinder walls are lubricated by splashing oil thrown off from the connecting-rod bearings.
(iii) Full Force Feed
-In a full force-feed lubrication system; the main bearings, rod bearings, camshaft bearings, and the
complete valve mechanism are lubricated by oil under pressure.
-In addition, the full force-feed lubrication system provides lubrication under pressure to the pistons and
the piston pins.
-This is accomplished by holes drilled the length of the connecting rod, creating an oil passage from the
connecting rod bearing to the piston pin bearing.
-This passage not only feeds the piston pin bearings but also provides lubrication for the pistons and
cylinder walls.
-This system is used in virtually all engines that are equipped with full-floating piston pins.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
2. Dry sump lubrication system
-In a dry sump, extra oil is stored in a tank outside the engine rather than in the oil pan.
-There are at least two oil pumps in a dry sump
-One pulls oil from the sump and sends it to the tank and the other takes oil from the tank and sends it to
lubricate the engine.
-The minimum amount of oil possible remains in the engine.
Dry sump systems have several important advantages over wet sumps:
(i) Because a dry sump does not need to have an oil pan big enough to hold the oil under the engine, the
main mass of the engine can be placed lower in the vehicle.
(ii) The oil capacity of a dry sump can be as big as you want.
(iii) In a wet sump, turning, braking and acceleration can cause the oil to pool on one side of the engine.
(iv) Excess oil around the crankshaft in a wet sump can get on the shaft and cut horsepower.
Sample Questions
1. What is the importance of lubrication in I.C. engines?
2. What are the various desired properties of a lubricant?
3. Explain how additives help to achieve the desired properties?
4. Explain wet sump lubrication systems with the help of neat sketches.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
OIL FILTRATION SYSTEMS
Bypass oil filtration system
-Most of the oil flows directly from the oil pan to the engine's working parts, and a smaller proportion of
the oil is sent through the filter via a second flow path in parallel with the first.
-The oil is thus filtered over time.
Full-flow oil filtration system
-All of the oil flows through the filter before reaching the engine's working parts.
-All of the oil is cleaned on its every circuit through the engine.
Valves
-Most pressurized lubrication systems incorporate an overpressure relief valve to allow oil to bypass the
filter if its flow restriction is excessive, to protect the engine from oil starvation.
-Filter bypass may occur if the filter is clogged or the oil is thickened by cold weather.
-The overpressure relief valve is frequently incorporated into the oil filter.
-Filters mounted such that oil tends to drain from them usually incorporate an anti-drain back valve to
hold oil in the filter after the engine is shut down.
-This is done to avoid a delay in oil pressure buildup once the system is restarted; without an anti-drain
back valve, pressurized oil would have to fill the filter before travelling onward to the engine's working
parts.
-This situation would cause rapid wear of moving parts due to lack of oil in the meantime.
TYPES OF OIL FILTERS
(a)Mechanical
-Mechanical designs employ an element made of pleated filter media to entrap and sequester suspended
contaminants.
-As material builds up on the filtration media, oil flow is progressively restricted.
-This requires periodic replacement of the filter element (or the entire filter, if the element is not
separately replaceable
(b) Cartridge and spin-on type
-Cartridge (or replaceable element) construction, has a permanent housing which contains a replaceable
filter element or cartridge
-The housing is mounted either directly on the engine or remotely with supply and return pipes
connecting it to the engine.
-The spin-on oil filter design has a self-contained housing and element assembly which is to be unscrewed
from its mount, discarded, and replaced with a new one.
-This makes filter changes more convenient and potentially less messy.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
(c) Magnetic
-Magnetic filters use a permanent magnet or an electromagnet to capture ferromagnetic particles.
-An advantage of magnetic filtration is that maintaining the filter simply requires cleaning the particles
from the surface of the magnet.
(d) Sedimentation
-A sedimentation or gravity bed filter allows contaminants heavier than oil to settle to the bottom of a
container under the influence of gravity.
(C) Centrifugal
-A centrifugal oil cleaner is a rotary sedimentation device using centrifugal force rather than gravity to
separate contaminants from the oil, in the same manner as any other centrifuge.
-Pressurized oil enters the center of the housing and passes into a drum rotor free to spin on a bearing and
seal.
-The rotor has two jet nozzles arranged to direct a stream of oil at the inner housing to rotate the drum.
-The oil then slides to the bottom of the housing wall, leaving particulate oil contaminants stuck to the
housing walls.
-The housing must periodically be cleaned, or the particles will accumulate to such a thickness as to stop
the drum rotating. In this condition, unfiltered oil will be recirculated.
OIL PUMPS
(a) Gear type
-Gear-type oil pumps have a primary gear that is driven by an external member, and which drives a
companion gear.
-Oil is forced into the pump cavity, around each gear, and out the other side into the oil passages.
-The pressure is derived from the action of the meshed gear teeth, which prevents oil from passing
between the gears, forcing it around the outside of each gear instead.
-The oil pump incorporates a pressure relief valve, spring-loaded ball that rises when the desired pressure
is reached, allowing the excess oil to be delivered to the inlet side of the pump.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
(b) Rotor type
-A rotor-type oil pump for sucking and discharging oil to be supplied to a variety of oil-requiring parts of
an automotive engine.
-The oil pump comprises a generally annular outer rotor which is rotatably disposed an external gear
which is partly in mesh with the internal gear of the outer rotor.
-The outer rotor is designed such that stress at the tooth base section of the internal gear is generally equal
to stress at the tooth base section of the external gear of the inner rotor in their dynamic condition, thereby
reducing the thickness of the tooth base section of the outer rotor.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
(c)Vane type
-A rotary vane vacuum pump is an oil-sealed rotary displacement pump.
The pumping system consists of;
(1) A housing
(2) An eccentrically installed rotor
(3) Vanes that move radially under spring force
(4) The inlet and outlet
-The outlet valve is oil-sealed.
-The inlet valve is designed as a vacuum safety valve that is always open during operation.
-The working chamber is located inside the housing. Rotor and vanes divide the working chamber into
two separate spaces having variable volumes.
-As the rotor turns, gas flows into the enlarging suction chamber until it is sealed off by the second vane.
-The enclosed gas is compressed until the outlet valve opens against atmospheric pressure.
-In the case of gas ballast operation, a hole to the outside is opened, which empties into the sealed suction
chamber on the front side.
Operating fluid, oil
-Pump oil, which is also called as operating fluid, has multiple tasks to perform in a rotary vane pump.
-It lubricates all moving parts, fills both the harmful space under the outlet valve as well as the narrow
gap between inlet and outlet.
-It compresses the gap between the vanes and the working chamber and additionally ensures an optimal
temperature balance through heat transfer.
Multi-stage pumps
-Rotary vane vacuum pumps are built in single and two stage versions.
-Two-stage pumps achieve lower ultimate pressures than single-stage pumps.
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Kenya Institute of Highways and Building Technology
Diploma in Mechanical Engineering, Automotive Option, Module II
Engine Technology; Lubrication Systems
06/06/2023
By Edward Ongeri
-Moreover, the effects of the gas ballast on the ultimate pressure are lower, as the ballast gas is only
admitted in the second stage.
Vacuum safety valve
-Depending upon the type of pump in question, rotary vane vacuum pumps can be equipped with a
vacuum safety valve.
-The vacuum safety valve disconnects the pump from the vacuum recipient in the event of intentional or
unintentional standstill, and uses the displaced gas to vent the pumping system in order to prevent oil
from rising into the recipient.
-After switching on the pump, it opens after a delay once the pressure in the pump has reached the
approximate pressure in the recipient.
Sample KNEC Questions
1)
a) Explain the meaning of the following properties of lubricants: (6 Marks)
i) Viscosity
ii) Oiliness
iii) Viscosity index
b) Explain each of the following principals of lubrication (4 Marks)
i) Hydraulic lubrication
ii) Boundary lubrication
c) With the aid of a sketch, describe the operation of splash type engine lubrication (10 Marks)
2)
a) Outline five causes of engine oil deterioration in a motor vehicle. (5 Marks)
b) Explain the meaning of the following properties of lubricant as applied to lubrication. (5 Marks)
i) Viscosity index
ii) Body
iii) Flow
c) Explain the differences between dry sump and wet sump types of lubrication system and state
where each is commonly used. (5 Marks)
d) With the aid of a diagram, illustrate the forced feed method of lubrication. (5 Marks)
3)
a) State three functions of the engine lubrication system (3 Marks)
b) Explain two differences between wet and dry liners used in engine construction (4 Marks)
c) With the aid of a labelled diagram, explain the operation of an external gear pump used in engine
lubrication. (13 Marks)
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