Automotive mechanics (volume i)(part 2, chapter11) engine lubricating systems

Enginelubricating systems 163 Engine lubrication 164 Oil circulation 165 Oil pumps 167 Oil pump service 169 Oil filters 170 Oil coolers 171 Lubrication of engine bearings 173 Crankcase ventilation 174 Lubricatingsystem maintenance 175 Lubricatingsystem problems 177 Technical terms 178 Review questions 178

Engine-lubricating systems

Chapter 11

Engine lubrication

Oil circulation

Oil pumps

Oil pump service

Oil filters

Oil coolers

Lubrication of engine bearings

Crankcase ventilation

Lubricating-system maintenance

Lubricating-system problems

Technical terms

Review questions

The engine-lubrication system is responsible for

distributing oil to all parts of the engine While oil in

the engine reduces friction and prevents wear, it does

much more Improved engine oils, together with the

design of engine-lubricating systems, have generally

extended the periods between services and also

increased the service life of engines.

Engine lubrication

Figure 11.1 shows how the main parts of an engine are

lubricated by oil pumped to them from the oil pan The

oil reaches the various parts through pipes, passages,

drillings, holes and grooves These, together with the

oil pump, oil filter and oil pan, make up the lubricating

system of the engine.

The main parts of the engine are provided with

positive lubrication, as shown They receive oil directly

under pressure, and so are referred to as being

pressure-fed Other parts that are not as heavily loaded are

lubricated with oil that is sprayed through a hole or jet.

Some parts of the engine do not require pressure

lubrication These receive lubrication from oil on its

way back to the oil pan Other parts depend on the oil

mist that is present in the crankcase when the engine is

operating.

Functions of lubricating oil

Engine-lubricating oil performs the following functions:

1 minimises wear

2 reduces friction and power loss

3 removes heat

4 reduces engine noise

5 forms a seal

6 cleans.

Oil minimises wear

With proper lubrication, all the parts that are subject to wear are separated by a thin layer of oil The oil prevents metal-to-metal contact so that there is minimum wear This is illustrated in Figure 11.2 which shows how oil is needed between the connecting-rod bearings and the crankshaft journals, and also between the pistons and cylinder walls.

Without proper lubrication, the bearings would wear quickly and eventually fail, causing damage to the crankshaft and other engine parts.

Shortage of oil on the cylinder walls would cause excessive wear and scoring of the cylinders, pistons and piston rings.

figure 11.1 Lubricating oil from the oil pan is pumped throughout the engine HYUNDAI

Oil reduces friction and power loss

All the moving parts of the engine are provided with

oil, and this reduces the friction between surfaces that

are in contact Less friction means less power loss

within the engine.

There is still some friction in the engine, but this is

fluid friction between the layers of oil, and is much

less than dry friction.

Oil removes heat

The oil is being continuously circulated throughout the

engine, and while it lubricates the various parts, it also

removes heat from them and carries it back to the oil

pan Heat from the oil pan is dissipated into the

surrounding air.

Some engines are fitted with an oil cooler This is

used to transfer heat from the engine oil to the cooling

system, or to the atmosphere This reduces the oil

temperature.

Oil reduces engine noise

There is always some clearance between the bearings

and journals, and between other working parts When

the load on a part is suddenly increased, the oil

between the parts acts as a cushion to absorb the shock

and reduce the noise.

Oil forms a seal

Piston rings must form a gas-tight seal between the

piston and the cylinder wall The oil on the cylinders

helps by filling the very small irregularities in the

surfaces At the same time, the oil on the cylinder

walls lubricates the pistons and rings.

Oil cleans

As it flows through the engine, the oil tends to carry away any particles of carbon or foreign matter and take them back to the oil pan Heavier particles drop to the bottom of the oil pan Lighter particles are removed by the oil filter.

Most of the cleaning is done by chemical detergents in the oil which keep engine parts clean, and by dispersants which hold particles suspended in the oil so that they are not deposited on the internal parts of the engine.

Oil circulation

The lubricating system of an overhead-camshaft engine is shown as a block diagram in Figure 11.3 The arrows show how the oil flows in the various parts of the system.

Figure 11.4 is a similar lubricating system, but this

is an engine diagram, which shows how the oil reaches

figure 11.2 Oil fills the very small irregularities in the

surfaces – it reduces friction in bearings and helps seal pistons and rings

figure 11.3 Block diagram showing the oil flow in an

engine-lubricating system

the actual engine parts In both diagrams, oil flow

starts at the oil pan and, after circulating through the

engine, returns to the oil pan.

The various parts of the lubricating system are

listed below Using this as a reference, the oil flow

should be followed through the block diagram and also

through the engine diagram.

Oil circulates through the lubricating system as

follows:

1 Oil pump The oil pump is driven by the engine It

takes oil from the oil pan through the strainer and

suction pipe and delivers it to the filter The

strainer prevents foreign matter from reaching the pump.

2 Relief valve The relief (or regulator) valve regu-lates the pressure in the system When the pressure specified for the engine is reached, the relief valve opens to prevent any further increase in pressure Surplus oil is then bypassed to the intake side of the pump.

3 Oil filter All the oil which leaves the pump is filtered before entering the engine The filter removes particles of carbon and any other matter in the oil and so protects the engine.

figure 11.4 Engine-lubricating system for an overhead-camshaft engine

1 strainer, 2 suction pipe, 3 crescent oil pump, 4 regulator valve, 5 oil filter, 6 main oil gallery, 7 main-bearing

journal, 8 crankpin journal, 9 passage to rocker gear, 10 rocker arm, 11 exhaust rocker shaft, 12 camshaft MAZDA

The filter has a bypass valve which opens if the filter becomes blocked This allows unfiltered oil to

pass into the system so that the engine is not

starved of oil.

4 Main oil gallery The main oil gallery is a passage

that runs the full length of the crankcase A number

of drillings and passages from the gallery service

other parts of the lubrication system.

In Figure 11.4, a passage from the main oil gallery carries oil to the overhead camshaft and

valve gear, and a drilling through each of the

crankcase webs supplies oil to the main bearings.

5 Crankshaft main bearings Each of the five main

bearings is supplied with oil through a separate

drilling from the main oil gallery.

6 Connecting-rod bearings Drillings in the

crankshaft carry oil from the main bearings to

the connecting-rod bearings Some oil leaves the

connecting-rod bearings and is thrown around as a

mist, and this helps to lubricate the internal parts of

the engine.

7 Oil jet An oil jet is used to lubricate the cylinder

walls and pistons (Figure 11.5) A small hole in the

side of the connecting rod is arranged to line up

with the oil drilling in the crankpin journal As this

occurs, a spray of oil is directed onto the cylinder

walls This happens once in each crankshaft

revolution.

8 Camshaft bearings The camshaft receives its oil

supply from the main oil gallery In the arrangement

shown in Figure 11.4, there are separate rocker

shafts for the intake and exhaust valves The oil to

lubricate the camshaft bearings is carried through

the hollow rocker shaft to the camshaft bearing caps,

where drillings take it to the camshaft bearings.

9 Rocker shafts Drillings in the rocker shafts provide oil to the rocker arms and these, in turn, have a small drilling to provide lubrication to the cams (Figure 11.6).

figure 11.5 When a hole in the connecting rod aligns with

a hole in the crankpin, oil is sprayed onto the cylinder wall to lubricate the piston and rings

figure 11.6 Lubrication of rocker arms and cams MAZDA

oil drilling

oil pool on cylinder head camshaft

10 Cams As well as receiving oil directly from the rocker arms, the cams and the other parts are lubricated by splash The cylinder head under the camshaft is shaped to form an oil reservoir from which oil is splashed by the cams to lubricate the cam surfaces, valve stems and valve springs.

11 Timing chain Where a timing chain is fitted, oil is provided from the end camshaft bearing or similar source so that the chain and sprockets are lubricated.

12 Return oil After lubricating the various components, oil from the cylinder head drains back to the oil pan through oil drain holes provided for this purpose Oil from the crankshaft drops directly back to the oil pan.

Oil pumps

There are three designs of oil pumps The basic arrangements are shown in Figure 11.7 They are:

1 gear pumps

2 crescent-type pumps

3 rotor pumps.

■ Oil pumps can be driven by gears or by a chain, or directly from the crankshaft.

Gear pumps

A gear pump, as shown in Figure 11.8, has two gears:

a drive gear and a driven gear The drive gear is fixed

to a shaft and is driven by gears from the engine’s

camshaft The driven gear is mounted on a stationary

shaft and is rotated by the drive gear.

When assembled, the gears are contained within the pump body by the lower cover The strainer is attached

to the pump inlet, which is part of the cover, and immersed in oil in the oil pan.

In operation, oil enters the pump inlet through the strainer and is carried around between the gear teeth and the body of the pump to the outlet, where it is delivered from the top of the pump into the lubricating system.

Crescent pump

The crescent pump shown in Figure 11.9 has an external toothed gear meshed with an internal toothed gear Some of the teeth of the gears are in mesh, but the others are separated by a crescent-shaped part of the pump housing.

The pump is mounted on the front of the crankcase with the inner gear on the end of the crankshaft, so that the pump is driven directly from the crankshaft.

When the pump is operating, oil is taken in through the intake port and is carried around between the gears and the crescent to the outlet port.

■ The oil pump of the engine-lubricating system shown in Figure 11.4 is a crescent-type pump.

Rotor pump

The pump housing is bolted to the front of the crankcase It has an inner rotor and an outer rotor (Figure 11.10) The inner rotor is mounted on the crankshaft and so rotates whenever the engine is running The lobes of the inner rotor fit into the outer rotor which is rotated in the housing.

figure 11.7 Three basic designs of oil pumps

housing

driven gear

drive gear

(a) Gear pump (b) Crescent pump (c) Rotor pump

crescent outer gear

inner gear inner rotor outer rotor housing

figure 11.8 Gear-type oil pump driven by a shaft

1 upper shaft, 2 pump body, 3 driven gear,

4 gear shaft, 5 drive gear, 6 cover, 7 strainer

Oil is taken into the pump through an inlet pipe and

strainer and carried around between the lobes of the

rotors to the outlet port A relief valve in the pump

body controls the pressure in the system.

Oil pump service

Under normal circumstances, an oil pump would only

be serviced during a complete engine overhaul.

The pump and regulator valve would be cleaned,

and the gears and housing checked for scores and

wear The clearance between the gears and housing (or

rotor and housing) would be checked, as well as the

end clearance of the gears in the housing.

An example of checking the clearance of the gears

in the housing is shown in Figure 11.9, where feeler gauges are being used between the gear and the housing.

Oil pump relief valve

The oil pump is capable of supplying much more oil than is needed to maintain a pressure in the lubricating system To prevent excessive pressure developing, a relief valve is fitted to the oil pump or to the oil gallery.

The relief valve consists of a spring and plunger, which opens and closes a port to regulate the flow of oil A simplified relief valve is shown in Figure 11.11.

It works like this:

1 When the engine is started, the pump supplies oil to the system At engine idle speed, the port is closed

by the plunger All the oil from the pump enters the system and provides a low oil pressure.

2 As engine speed increases, the pump speed also increases and so more oil is delivered into the system This increases the pressure in the system Pressure acting on the top of the plunger moves it down its bore.

3 When the system reaches a certain pressure, which

is determined by the strength of the plunger spring, the plunger will have moved far enough to open the port.

4 Surplus oil, which is not needed to maintain pressure in the system, will then pass through the port and return to the intake side of the pump.

5 The plunger will open and close the port, as needed,

to release surplus oil and limit the pressure in the system Whether the port is open or closed will

figure 11.9 Crescent oil pump – clearance can be

checked where shown and also between the gears and crescent MAZDA

figure 11.10 Rotor oil pump

1 cover, 2 inner rotor, 3 outer rotor, 4 gasket,

5 housing, 6 relief valve assembly HOLDEN LTD

figure 11.11 Operation of an oil pressure relief valve –

pressure on top of the plunger is opposed by the spring

depend on the engine speed and the temperature of

the oil It will also depend on the condition of the

engine.

■ A relief valve is located in the housing of the oil

pump shown in Figure 11.10.

Why the system has pressure

Pressure builds up in the system because the oil pump

maintains a supply of oil, and also because of the

restrictions provided by the small bearing clearances

etc, which prevent the oil from flowing readily back to

the oil pan.

With worn bearings and large clearances, or if a

relief valve is stuck open or has a faulty spring, the

pressure in the lubricating system will be low If any of

these conditions occurs, the pump will be delivering to

its maximum capacity but will not be able to supply

enough oil to build up normal pressure.

■ Oil pressure depends on the pump delivering an

adequate supply of oil and the engine being in good

mechanical condition A badly worn engine will

have low oil pressure.

Oil filters

During engine operation, carbon particles, dust and

small metal particles become mixed with the

lubricating oil The oil filter keeps the oil clean by

removing these impurities which would otherwise find

their way through the oil passages to the bearings and

other surfaces.

A sectioned oil filter is shown in Figure 11.12 It

consists of a metal canister with a pleated-paper

element The element is porous to allow oil flow

with-out restriction, but the pores are fine enough to filter with-out

the impurities in the oil The canister is threaded on to a

tubular mounting on the engine block A rubber ring

provides a seal between the filter and its mounting.

The filter has a non-return valve at the open end of

the canister which prevents oil from draining from the

filter when the engine is stopped The valve is a rubber

disc that covers a ring of holes.

When the engine is running, oil flows into the filter

through the non-return valve holes to the outside of the

element It passes through the element to the inside of

the canister, then back to the engine through the

tubular mounting.

A bypass valve inside the canister is a safety valve,

which opens to allow oil to go straight through the

filter should the element become blocked.

Replaceable filter element

The filter assembly in Figure 11.13 has a replaceable filter element The filter housing is bolted to the engine block and the paper element is held in the housing by the filter cover.

The oil flow in the filter is similar to that of a canister filter.

figure 11.12 Construction of a canister-type oil filter

figure 11.13 Oil filter with a replaceable element

sealing ring

housing

filter element

O-ring cover

Full-flow and bypass filters

There are two filter arrangements: full-flow filters

and bypass filters Full-flow filters are mainly used,

but some diesel engines have a full-flow filter as the

main oil filter, and a bypass filter as a supplementary

filter.

Full-flow filter

Figure 11.14 shows the principle of a full-flow oil

filter All the oil delivered from the pump passes

through the filter on its way to the bearings and other

engine parts, so that only filtered oil is used for

lubrication A bypass valve is located in the filter so

that if the filter becomes clogged, the valve will open

and oil will still be supplied to the system.

■ Full-flow filters operate at engine oil pressure and

must be correctly tightened during servicing to

avoid oil leaks.

Bypass filter

The principle of a bypass filter is shown in Figure

11.15 This filters only a portion of the oil delivered

from the pump to the oilways of the engine and it operates at a lower pressure than a full-flow filter.

An oil line is tapped into the oil gallery and a restricted amount of oil is allowed to flow through the filter The oil from the filter is not delivered into the engine, but is bypassed and returned to the oil pan In this way, some oil is always being filtered, though not directly on its way to the engine parts.

Oil coolers

Oil coolers are heat exchangers, in which heat in the oil is transferred either to the engine coolant, or to the atmosphere.

There are two designs of oil coolers:

1 oil-to-coolant coolers

2 oil-to-air coolers.

Oil-to-coolant oil cooler

Both oil and coolant flow through this type of cooler, the two being separated by tubes or baffles of some type This enables heat to be transferred from the oil to the coolant because the oil is at a higher temperature.

An oil cooler and oil filter assembly for a small diesel engine is shown in Figure 11.16 Both the cooler and the filter are installed on the oil filter mounting on the cylinder block With this arrangement, oil from the oil gallery passes through the oil cooler before it enters

figure 11.14 Principle of a full-flow oil filter – all the oil

entering the system is filtered

figure 11.15 Principle of a bypass filter – some of the oil

from the pump is filtered and returned to the oil pan

figure 11.16 Oil-to-coolant type oil cooler and oil filter

assembly FORD

the filter, so that oil leaving the filter has been both

cooled and filtered.

The cooler has external connections for the coolant

hoses that connect it to the engine’s cooling system.

Oil-to-air oil cooler

This type of oil cooler is similar to a radiator in that

it has tubes and fins (Figure 11.17) Oil from the

lubrication system is circulated through the cooler, and

air is directed across the tubes and fins In this way,

heat is removed from the oil and its temperature is reduced.

The cooler is located in the engine compartment where it will get an adequate flow of air, usually near the radiator.

Lubrication system with oil-to-coolant cooler

A lubricating system for a small diesel engine is shown

in Figure 11.18 This has an oil-to-coolant type cooler The cooler is mounted to the engine block and the oil filter is mounted on the cooler Oil flows through the cooler, then through the oil filter and on to the main oil gallery.

This system has other features that can be identified

in the illustration:

1 The oil pump is directly driven by the engine It is

a rotor pump, referred to as a trochoid-type gear pump.

2 The engine has balance shafts with bearings that are pressure-fed from the main oil gallery.

3 The engine has a timing chain which is supplied with oil from oil jets.

4 The system has piston-cooling jets which squirt oil upwards into the pistons to cool the piston head.

5 The engine valves have hydraulic tappets which are supplied with oil from the rocker shafts on top of the cylinder head.

figure 11.17 Oil-to-air type oil cooler TOYOTA

connecting hoses

oil inlet

air flow oil outlet

oil cooler

figure 11.18 Engine lubricating system with an oil cooler and other features FORD