PART ONE:

WORKING PRINCIPLES

The Starting Motor

It must first be understood that energy cannot be created from nothing; it can however be converted from one form to another.

In the case of the starter motor, we employ electrical energy – the electrical current from a battery – and convert it into mechanical energy, the type of energy required to turn over the engine of a motor vehicle.

To understand how this conversion is brought about – how we can use the battery current and produce turning movement – we must consider how two magnetic fields can interact and produce such a movement. We can then go back a stage further and see how these magnetic fields are produced from the battery current.

The Production Of Turning Movement

These illustrations, Figure 1, show two magnetic fields. The main one is produced by the horseshoe magnet and the second, which we shall call the 'armature magnetic field', exists around the bar magnet.

In the combined picture at the bottom, this bar magnet is pivoted at the centre.

Every time the two magnets are brought into close proximity to each other, their fields interact, become distorted and, in trying to revert to normal, force the pivoted magnet into movement.

Figure 1. The production of turning movement.

But the movement will be restricted: the bar magnet will turn only as long as like magnetic poles are next to one another. You can see that the two North Poles repel each other, so do the two Souths producing the turning move-ment. (You will remember this fundamental rule of magnetism.) But, when the magnet has rotated through half a revolution, unlike poles will be together and no further movement will occur. One way to continue the rotation would be suddenly to reverse the polarity of the bar magnet i.e. change over the North and South poles.

The Magnetic Effect Of An Electric Current

In the build-up of our starter motors, we do not use per-manent magnets to produce the two magnetic fields: we make use of the electric current from the vehicle battery.

Figure 2. Illustrating the magnetic effect of an electric current taken from a battery.

Here we show current passing through a conductor in the direction indicated by the arrow. A magnetic field will be produced around the conductor. The lines of force of the magnetic field are formed in a definite pattern, dependent upon the direction of the current flow. In this case, the pattern is anti-clockwise in form, as we have indicated by the circular arrows.

A cross-section of the wire is also shown, illustrating the circular pattern of the magnetic field.

Concentrating The Magnetic Field

Using a coil of wire instead of a single conductor greatly increases the magnetic effect. The soft iron core adds to this by concentrating the lines of magnetic force into the coil area. The result is a powerful magnet.

Figure 3. Concentrating the magnetic field.

The polarity of the magnetic field varies with the direction of the current flow. In this particular case the current flowing from battery positive through thee coil to the negative produces a North pole on the left and a South on the right. If the battery were connected the other way round, thus reversing the current flow through the coil, the polarity of the field would also be reversed.

Having established that a magnetic field can be produced round a coil of wire, let us consider how we employ two such fields in the starter motor.

We will deal first with the main magnetic field – if you remember, this was provided by the horseshoe magnet in our original simple illustration, Figure 1.

Production Of The Main Magnetic Field

The main field is created by using soft iron which be-comes easily magnetised by current flowing through the surrounding coils of wire. These coils are known as field coils and the blocks of soft iron, specially shaped to con-centrate the magnetic strength into the gap, are called pole-pieces or pole-shoes.

All we have done in effect is to cut the soft iron of the previous illustration into two halves and shape the end of each half. In addition, the coil winding has been divided into two. The windings are so arranged that the pole-pieces are of opposite polarity.

Figure 4. Production of the main magnetic field.

In this particular case, a north pole is formed on the left and a south on the right. The field magnets we have pro-duced remain fixed at this polarity.

Producing The Armature Magnetic Field

And now let us consider the second magnetic field, generally termed the 'armature magnetic field'. You will remember that this was formed by the pivoted bar magnet in our early illustration, Figure 1.

This loop of wire, passing battery current, produces an equivalent effect. The current flow in the wire gives rise to a magnetic field whose plane is at right angles to the loop itself – as we have indicated by the shaded area, which you can consider as representing our original bar magnet.

With the current flowing round the loop in the direction shown by the arrows, a north magnetic pole will be pro-duced on the left, and a south on the right. If we reversed the current flow, we should also reverse these poles.

Figure 5. Producing the armature magnetic field. Above right.

Interaction Of The Two Magnetic Fields

Here we show the armature loop in the magnetic field of the main magnet. The two fields interact, the two norths and the two souths repelling one another, thus forcing the pivoted loop into movement.

If the battery current still remains in the same direction, the loop will cease rotating after half a revolution, that is when the north and south poles line up.

Figure 6. The interaction of two magnetic fields.

However, if we could arrange matters so that as the loop turn so the pole coming round to the fixed north pole of the field magnet was itself always north; and that app-roaching the fixed south pole was always south, the repelling action would invariably take place, continually impulsing the loop as it rotated.

The Principles Of Commutation

This effect is achieved by joining the ends of the loop to two metal segments before they pick up the battery current.

Brushes actually form the contact between the battery and the segments.

Let us consider the top left hand illustration first, where the black half of the loop is at the top, with its end connected via the segment to positive battery.

In this position, the current flowing through the loop produces a north pole opposite the fixed north pole of the field magnet; and a south opposite the fixed south pole. Repulsion occurs and – the loop begins to rotate.

Figure 7. Explaining the principles of commutation. Note that the two sketches certainly are different.

Now look at the bottom right-hand sketch, where you will see that the loop has moved through half a turn, so that the white section is now on top. But, you will notice that the magnetic field produced by this section is still north in polarity; in other words it will still be repelled by the fixed north pole. Likewise, the black section of the loop which previously produced a north pole, is now producing a south as it moves opposite the fixed south pole. Repul-sion will therefore occur again and the rotation will continue.

What has happened is that the direction of the current in the wire itself has changed because the segments have moved under brushes connected to opposite sides of the battery. You can see in the left-hand illustration that the black half of the wire loop is connected to positive at the battery; whereas in the right hand illustration it is con-nected to negative at the battery, which means that the current flow in that section has reversed. The same can be said for the other section.

With a change in the current, comes a change in polarity. As the loop rotates, therefore, the two sections assume the polarity of the fixed poles they approach.

We shall be discussing this reversal effect, known as commutation, a little later on.

Opposing Fields

Let us examine this interaction of the two magnetic fields a little more closely, to give you a more graphic idea of how the turning movement is produced.

Figure 8 shows the main field produced by the north and south pole pieces. We also show, in cross-section, the magnetic lines of force surrounding the armature loop.

Imagine the current at 'A' flowing through the conductor towards you. The magnetic lines of force produced around 'A' in an anti-clockwise direction will interact with the lines of force of the main magnetic field between the north and south pole-pieces. The result of this interaction between the two fields is a distortion of the lines of force. A strengthening of the field occurs under the conductor at point 'A'.

Figure 8. Opposing fields.

Now magnetic lines of force have elastic properties, and, if we regard these distorted lines of force as stretched elastic threads which tend to straighten themselves, we can see that a pressure will be exerted under the conductor at point 'A' and the loop will be urged round in a clockwise direction.

Similarly, it can be seen that at point 'B', where the current through the conductor and hence the magnetic field is in the opposite direction, that a strengthening of the field will occur above the conductor and the pressure exerted will assist the movement of the loop in a clockwise direction.

Thus by the interaction of two opposing magnetic forces, mechanical energy or more specifically turning move-ment has been produced from electrical energy.

We shall now consider the more practical aspects of the starter motor, beginning with the production of the main magnetic field.

The Main Field In Practice

The theoretical motor we have discussed so far used a main magnetic field of one North and one South pole. In practice, the majority of our machines use four pole shoes surrounded by field coils, thus producing a concentrated field with four magnetic poles.

Figure 9. The main field in practice.

The field coils are wound so as to produce alternate North and South poles.

The two brushes and the main terminal visible in this picture, Figure 9, are the means by which the battery current enters and leaves these field coils.

In this particular arrangement, the four coils are wound in series, i.e. the current passes in line from one coil to the next. As this current is normally in the region of 200-300 ampéres, heavy copper strip is used for the coil windings. For the same reason, two brushes are necessary, each taking half the total current consumption, to avoid elec-trical losses and overheating. The brushes themselves contain a high percentage of copper mixed with the carbon. We shall be referring to these two brushes from now on as the insulated brushes. You can see that the leads to them are covered by fairly heavy braiding.

Earth Brushes

A corresponding pair of non-insulated or earth brushes is also used in the starter, again with the aim of passing the heavy currents without excessive losses which result in overheating.

Figure 10. Brushes riveted to a starter motor's end cover.

When we deal with the starter circuit, you will see exactly at what point these earth brushes fit into the picture.

The Armature

The second magnetic field in our starter motor is prod-uced in practice by this armature which, although far removed in appearance from our simple wire loop and two segments, is essentially the same. Instead of one loop, we use many, but each end of every loop is still connected to a copper segment. All the segments are insulated from one another and rolled together to form what is called a commutator. This provides the running surface for the brushes which carry current to and from the armature windings.

The whole assembly is built round a solid steel shaft. The core, which actually carries the windings, consists of a whole series of soft iron laminations. (You will remember how iron helps to concentrate the magnetic field.)

Laminations are used instead of solid metal, to reduce the heating effect of harmful electric currents known as 'eddy currents' which are produced when the armature revolves in the main magnetic field. The laminations offer a sufficiently high resistance to render these currents harmless as far as heating effect is concerned.

Figure 11. The armature.

Having shown you the complete assembly, let us examine the components more closely.

Individual Armature Components

In Figure 12 you see the individual components. Let us commence with the steel shaft which forms the centre of the whole assembly. The short splined section on the left carries the commutator. The next splined section is larger in diameter and longer to carry the soft iron laminations of the core. The heavy splined section on the right does not concern us at this stage as it forms part of the drive assembly.

Figure 12. The armature components.

The commutator is built up of individual copper segments, with an insulating strip between adjacent segments.

The commutator 'risers' provide convenient soldering points for the ends of the armature loops.

These armature loops, aptly termed 'hairpins', pass through the slots in the laminations; the ends are then twisted so as to connect with the correct commutator segment.

To continue our study of the starter motor, we must examine the method of interconnecting the individual loops in the complete armature winding.

Method Of Armature Winding

In Figure 13, we have reduced the number of loops in the winding so as to simplify matters, which also means of course that we reduce the number of segments in the commutator accordingly. Our aim is to illustrate the order in which each loop is connected.

If we start at segment 1, we can follow the lower loop round to the back of the commutator where it ends at segment 2. A second loop then continues the winding round to segment 3. From 3, we pass to 4; from 4 to 5 and so on.

Figure 13. Method of armature winding.

You will notice that the ends of each loop are staggered to opposite sides of the commutator, being in practice always 180° apart, less one segment.

This method of winding is known as 'wave winding'.

The Armature Magnetic Poles

Here you see the magnetic poles produced by these windings. The current flow in them is such that two north poles are formed at the exterior of the armature and on opposite sides.

If you imagine the remainder of the windings in position round the armature, at right angles to the ones shown, the current flow in them would be arranged to produce two south poles.

Figure 14. The armature magnetic poles.

The total effect would be to produce four alternate north and south poles round the exterior of the armature.

These are the four magnetic poles which oppose those of the main field of the pole-pieces.

The Opposing Magnetic Poles

Here the illustration shows the opposing polarities of the two magnetic fields. The main field produced by the four pole pieces is shown surrounding the alternate north and south poles of the armature field.

Figure 15. The opposing magnetic poles.

You will remember that the poles must oppose one an-other for repulsion to occur and the armature to rotate.

The Armature – Wave Winding

Although this diagram may appear complicated at first sight, it merely represents in diagrammatic form what we have already shown you – that is, the method of inter-connecting the individual loops in the wave-wound armature.

Figure 16. The armature, wave winding explained.

We shall go a stage further and follow the path for the battery current round the armature from where it enters at one of the positive or earth brushes to the adjacent insulated or negative brush – i.e. the point at which the current leaves the armature.

Let us follow the windings, commencing from the positive brush, in position on the No. 1 segment. The first loop carries the current to the No. 2 segment at the opposite side of the commutator. You can see that the two ends of the loop are 180° opposed, less one segment. From segment 2, the winding loops round to 3 – that is the segment next to the starting point. The current path con-tinues to segment 4 and from there to 5; from 5 to 6 and so on to number 11, which is the segment under the negative brush. This completes one path for the current from one positive brush to one negative.

But we have simplified matters here for the sake of clarity; there is actually another current path from the positive brush on segment 1 round the armature in the other direction to the negative. This means that the battery current is passing through the whole of the armature windings, producing a strong magnetic field.

The magnetic effect will further be multiplied by the current flowing between the other two positive and negative brushes which we have omitted. These two are joined in parallel with the ones shown here and will be passing half the total current consumption of the starting motor.

In a production model, there are usually nine commutator segments between brushes of opposite polarity, which of course further increases the number of armature wind-ings and accordingly the magnetic effect. Wave-winding the armature in this way, puts all the windings in circuit when the brushes are passing current.

Commutation

In the last diagram, we followed the current path round the armature between one positive and one negative brush; but we considered it in a stationary position. We must now show what happens when the armature begins to turn.

Figure 17. Brushes in contact with segments 1 and 11.

Look at the top illustration first. It shows the brushes in position on segments number 1 and number 11 – in other words the brush – segment relation is that of the previous picture. But we have dispensed with the windings not immediately concerned with the changes that take place when the armature begins to rotate. Thus segment 3 is joined directly to segment 11, instead of being, looped via the intermediate segments, 5, 6, 7, 8, 9 and 10.

In the top illustration then, current enters the armature via the positive brush on number 1 segment. Here the current splits into two, one half indicated by the arrowed black line travelling clockwise via segment 2 to segment three; then still clockwise from 3 via 4 to 11. The other half of the current would travel round an equal number of windings to the negative brush on segment 11, but in the opposite direction. The start and finish of these other windings is shown by the short arrowed white lines (A).

Now consider the lower illustration. The armature has rotated so that the brushes are now on segments ad-jacent, to the previous ones – i.e. positive brush on segment 3; negative on segment 13.

Now, you will remember from our earlier simple illust-ration of commutation that for the armature to continue rotating the magnetic poles produced by it must always oppose the fixed poles of the main field magnets. In other words, some change must take place to maintain this repulsion by like poles.

Figure 18. Current flow into segment 3.

In the lower illustration (Figure 18) then, current will now flow into the armature at segment 3. It will split as before into two halves, one half continuing clockwise round the armature via segment 4 to segment 11 – i.e. in the same direction as before in this part of the winding. The current flow continues clockwise from 11 via 12 to 13 taking in an additional loop and segment.

But the other half of the current is anti-clockwise in direction from segment 3, travelling round the loop via segment 2 back to segment 1 – i.e. it opposes the previous flow in these two loops – just look at the top illustration again and see how the direction of the current has changed from clock to anti-clock.

Summing up then: while the current flow in these two loops has reversed, the overall effect is to maintain the same direction of current in all the other windings. Mag-netically, this means that the original polarity of the four armature poles has not altered despite the fact that the armature itself has rotated one set of segments. If then, armature north poles were originally produced opposite the main north poles, the same condition would remain in the new position and repulsion would again occur to continue the rotation.

In practice, therefore, we can consider that the com-mutator, in reversing the current flow in two loops, ensures that the original magnetic pattern of the armature field remains constant, north poles invariably being repelled by north poles; south poles invariably being repelled by south poles.

The exact moment at which the reversal of the current occurs in the two loops is all important to the correct running of the starter motor in service.

It is arranged to take place when two adjacent segments are making contact with the same brush. As the brushes are wide enough to cover two segments, this condition is al-ways present no matter what the position of the armature.

Figure 19. Positive brush in contact with segments 1 & 3.

In Figure 19, we show the positive brush making contact with segments 3 and 1. This effectively shorts out the two loops between these segments at the moment when the current reversal is taking place. The commutation may be regarded as perfect if the reversal is completed before segment 1 is clear of the brush. On the other hand if this segment leaves the brush before the complete reversal of the current, sparking will occur between the brush and segment, which will be extremely injurious to both.

Brush Positioning

A further word now about the positioning of the brushes in relation to the magnetic fields. For the sake of clarity we shall once more revert to our early two pole example.

As we have seen, in the starter motor there are two fields; the main field shown in the top picture and the armature magnetic field shown in the bottom picture, Figure 20.

These fields are at 90° to each other, the main field running horizontal, the armature field vertical.

Figure 20. Main and armature magnetic fields.

You will observe that in the second illustration the main concentration of the magnetic field is centred round those conductors opposite the pole shoes, leaving neutral points along the vertical line. This is normally referred to as the 'Geometric Neutral Plane'.

Figure 21. The magnetic neutral plane.

The starter brushes must be positioned in the neutral plane to prevent excessive sparking taking place when current is passing between them and the commutator segments.

But a complication arises. The two magnetic fields of the starter motor cannot possibly co-exist without some in-teraction. We stated right at the beginning that the turning movement was actually due to this interaction between the two fields.

The resultant field is shown in Figure 21. You will notice immediately that the neutral plane is no longer vertical: it has moved due to the flux distortion. The neutral points, in which the brushes must be positioned, have been moved against the rotation of the armature – and, to obtain spark-less commutation the brushes must follow suit. We have indicated the correct brush position, on the new neutral plane – technically known as the 'Magnetic Neutral Plane'.

If the rotation of the starter were now reversed, the neutral axis would swing over to the other side and the brush position would have to be altered to correspond. This theory has a direct practical bearing.

In the production of our starter motor components, the end brackets which hold the brushes are designed with clock and anti-clock fixing holes so that the brush position may be varied according to the rotation of the machine.

Starter Internal Circuit – (Series Field)

Let us now examine the internal arrangement of a typical starter motor with a view to tracing the circuit path through the fields and armature.

Figure 22. Starter internal circuit with series field.

You have already seen an actual photograph of the four field coils depicted here. You will remember they were wound so as to produce alternate north and south poles and that they were all in series with one another. If you start from the end of the black line at the top of Figure 22 and follow the winding through, you will see this is the case. The pair of insulated brushes then connect with the armature commutator. The circuit continues through the armature windings to the pair of non-insulated or earthed brushes, which we showed you earlier connected to the starter end-bracket.

This means therefore that the four field coils are electrically in series with the armature windings. Thus current flowing from the vehicle battery will at once energise the field coils and the armature, producing the necessary two opposing magnetic fields. This type of starter motor is known as a 'plain series motor'.

Starter Internal Circuit (Series Parallel Field)

Another internal arrangement used in our production Starters employs a series – parallel field.

Figure 23. Internal circuit with series-parallel field.

The field circuit is divided into two halves, each in parallel with the other, thus dividing the electrical load. Both halves of the circuit are, however, still in series with the armature windings, Thus this starter motor still remains a series type of machine.

By assembling the field coils in parallel, it is possible to pass a somewhat greater current and obtain an overall increase in the mechanical energy developed, or torque as it is called.

The Complete Electrical Circuit

Figure 24. The complete electrical circuit.

In Figure 24, you see the starter motor in circuit. The ex-ternal cable layout to the motor is shown, basically as it would appear on a vehicle. The two components that are necessary are the battery to supply the current and a switch to control the current supply to the starter motor.

We have used a plain series machine in this circuit, but it could be directly replaced by the series-parallel type.

Let us follow the circuit through, commencing at the battery. We shall assume that the starter switch is closed.

A heavy cable connects the battery to one side of the switch. The circuit continues across the contacts in the closed position to the starter motor. It carries on round the four field coils in series via the two insulated brushes to the armature. The pair of earth brushes complete the circuit through the metal of the starter end bracket to the body of the machine, which is bolted to the vehicle chassis or earth. This earth connects with the battery earth terminal which is also strapped to the chassis.

Torque

Figure 25. Explanation of the term torque.

Let us now take a closer look at the expression 'Torque', which is the term used to define the turning movement or effort produced by the starter motor.

A simple illustration will suffice to acquaint you with the significance of the term.

If a force of 20 lbs. is applied to an engine crankshaft through a leverage of 12 inches, the turning effort pro-duced would be:

20 x 1:20 lbs. ft.

The same unit of measurement i.e. lbs. ft. is used to express the turning effort developed by the starter motor when this effort is applied to the engine crankshaft via the flywheel.

But, to produce an equivalent 20 lbs. ft. torque at the engine crankshaft, the torque developed by the starter motor need only be 2 lbs. ft., due to the mechanical aid of gear ratio of 10 : 1 between flywheel and pinion.

Lock Torque Test

Figure 26. Principle of the starter torque test.

For test purposes, the torque produced by the starter motor is measured with the starter taking current, but with the armature shaft prevented from turning by a brake or clamp. The torque produced by the starter when trying to turn against this brake is termed the 'Lock Torque' and the test, quite logically, the 'Lock Torque Test'.

The measurement can be taken directly from the arm-ature shaft or via a test-bench flywheel.

Battery Capacity:

Its Importance In Relation To Engine Starting

In connection with the performance of the starter motor, the importance of the battery must not be forgotten. Owing to the very heavy current taken by the starter, there is quite an appreciable drop in the battery voltage. The performance of the starter motor is therefore largely dependent upon the size of the battery employed. A battery of ample capacity is essential, otherwise the heavy discharge current will result in an excessive volt-age drop which will limit the current available for the starter motor, and in turn reduce the torque developed.

In this case, you see, we need a current of 275 amps. at 9-volts. The top battery won't give us this current; it can only supply a maximum of 200 amps at this voltage. The other, larger capacity battery will, with some to spare.

Figure 27. Battery size requirement comparison.

The Transmission Of The Turning Effort

We must now show how the torque or turning movement we have produced is transmitted to the vehicle engine; in other words how the motor we have created becomes a starter motor.

Figure 28. An example of a starter drive arrangement.

Figure 28 shows you one of the many different types of starter drives. The pinion engages with the flywheel, thus transferring the turning movement of the starter armature shaft to the engine crankshaft.

Pinion And Flywheel

The pinion and flywheel can be seen in this picture. The pinion to flywheel ratios vary usually from 9:1 to 14:1 but are generally in the order of 9 or 10:1 on modern vehicles.

Figure 29. Showing starter pinion and flywheel ring gear.

Cranking Speeds

In order to turn this flywheel at sufficient speed to start the engine, a minimum 'cranking speed' of approximately 90 to a 100 r.p.m. is required. Cranking speeds are usually stated as 'cold cranking speed' or 'hot cranking speed'. Obviously the effort required to turn over a warm engine is far less than that for a cold engine, when the oil is thick.

Breakaway Torque

We must discuss one further term in connection with starter motors and engine starting in general:

'Breakaway Torque' – the torque required to move the engine from rest, that is to overcome friction, oil viscosity, compression etc.

This breakaway torque is usually of short duration, but it is evident that it represents the maximum turning effort the starter motor must produce. Fortunately, however, the main characteristic of the series motor is that it produces its maximum torque at the beginning of the starting operation, that is when it is most needed.

Graph – Torque, Speed, Current

Here we have plotted 'Torque' and 'Current' against speed in R.P.M. and indicated the starter terminal voltage.

You can see that the torque curve falls from the maximum as the speed of the starter increases. It is this character-istic which renders the series type of motor particularly suitable as an engine starting motor.

Figure 30. Torque, speed, current curves.

And furthermore, when the starter armature rotates in the magnetic field, a voltage known as a 'back EMF' will be induced into the windings, which is proportional to the speed of rotation. As this induced voltage is in an opposite direc-tion to the supply voltage, it opposes the latter. The current drawn from the battery therefore decreases as the speed of the motor increases. You can see this from the current curve. The starter terminal voltage will rise as the load decreases; and as the current drops, so the torque de-creases; in other words, the least torque is produced when the starting load is at a minimum.

One further characteristic of the series motor is that its speed varies appreciably with load variation. Particularly is this so with light loads, where the speed increases at a very rapid rate, so that under no-load conditions the motor may attain really dangerous speeds. These series motors should therefore never be allowed to run con-tinuously without load.

PART TWO –

LUCAS STARTERS' SYMBOLS AND MODEL INTERPRETATION

Current Production Starters

Having discussed the theory of the starter motor and explained several terms essential to the understanding of engine starting, we shall now show you the practical application of all this theory, dealing with the various types of Lucas Starters.

The power developed by our Light Car Starter Motors today may be as high as 22 lbs. ft. Lock Torque, (or the equivalent of 1½ B.H.P. at 1,000 r.p.m.). And the currents required to produce such high torques can be in the order of 400 amperes or more.

Symbols

We produce three main types of starters: the M35G.; the M418G., and the M45G.

The letter 'M' means in all cases starter motor: the number refers to the diameter of the yoke, and indicates that it is either 3·5", 4·125" or 4·5" in diameter. The final letter, as you can see, usually indicates some special feature, either a particular type of end bracket, a water-proofed machine etc.

Starter Symbols

Prefix M – Starter Motor

35 – 3½" Diameter

418 – 4⅛" Diameter

45 – 4½" Diameter

Suffix A – Pressed Metal C.E. Bracket

G – Die Cast C.E. Bracket

L – Long Type Machine

w – Waterproofed

The M35G. Starter

This machine is a 4-pole, 4-brush, series motor. It is produced either with the field coils wired in series or in series-parallel. The plain series arrangement is usually employed for the 12-volt machine, and the series-parallel for the 6-volt.

Figure 31. Illustration of the M 35 G starter motor.

The highest torque available from these 3½" models is approximately 9·3 lbs. ft. Lock Torque at 380 amps. for the 12-volt machine, and 6 lbs. ft. at 400 amps. for the 6-volt machine.

The M418G. And M45G. Starters

Both these starters are 4-pole, 4-brush machines with series-parallel fields. This arrangement of the field coils produces an overall increase in the torque developed. The maximum Lock Torque figures for the M4l8G. type are:

17 lbs. ft. at 450 amps. for the 12-volt machine and 9·25 lbs. ft. at 520 amps. for the 6-volt machine.

Figure 32. Upper – M418G starter; lower – M45G starter.

For the M45G. i.e. the 4½ inch machine, the 12-volt range have a maximum Lock Torque of 22 lbs. ft. at 440 amps. and the 6-volt range of 14 lbs. ft. at 550 ampéres.

In the next part we shall deal with the different types of drives used with the above range of starter motors.

PART THREE – STARTER DRIVES

Main Types Of Starter Drive

We have told you how the turning effort produced by the starter motor is transmitted to the engine flywheel by means of a starter drive and we shall now classify the various types, explaining the differences, both in con-struction and operation.

As far as the method of engagement is concerned, starter drives fall into three main groups: the inertia or 'crash' type, the pre-engaged type and the axial type.

For our purposes we shall deal mainly with the inertia drive, this being the type normally employed for cars and light commercial vehicles.

The 'Inertia' Or Crash Type Drive

Here you see a simple 'Inertia' or 'Crash-Type' drive. As the starter armature rotates, quickly reaching a high speed, the pinion, lagging behind the movement due 1o inertia, slides along a screwed sleeve into mesh with the flywheel teeth.

Figure 33. The Lucas inertia type of drive.

The pinion and sleeve assembly is carried on splines on the armature shaft, this arrangement allowing the sleeve to move along the shaft against the action of a heavy compression spring, thus absorbing the initial shock of engagement. The pinion is thrown back into the diseng-aged position when the speed of the flywheel is relatively greater than that of the pinion, that is when the engine speed exceeds the motor speed.

Inboard And Outboard Operation

According to the method of mounting, the pinion may be arranged to move towards the starter motor to engage the flywheel or away from the motor. The former arrangement is known as the inboard drive – that's the one you see at the top; the latter is the outboard drive.

Figure 34. Inboard (upper) and outboard (lower) types of starter drive units.

You will observe in the bottom picture that a special housing is necessary for outboard drives in order that an additional bearing can be provided to support the outer end of the shaft.

Four Main Types Of Starter Drives

Lucas make four main types of inertia drive :

The S, SB, the RSB (rubber coupling) and the Eclipse, with inboard and outboard models of each type. We shall now examine each type individually.

Figure 35. Main types of drives on Lucas starter motors.

The 'S' Type Drive

The shock load is here absorbed by the heavy compres-sion spring. A light retaining spring prevents the pinion from being vibrated into contact with the flywheel when the engine is running.

Figure 36. An example of Lucas 'S' type inboard drive.

The pinion of the inboard drive moves in towards the starter motor, that is from right to left in this picture.

Figure 37. An example of Lucas 'S' type outboard drive.

With the outboard drive the pinion moves outwards from the motor towards the end of the shaft.

The 'SB' Type Drive

Figure 38. An example of Lucas 'SB' inboard drive.

Figure 39. An example of Lucas 'SB' outboard drive.

The 'SB' drive is a later version of the 'S' type you have just seen. The pinion is here carried on a barrel type assembly which is mounted on a screwed sleeve. This sleeve is carried on splines on the armature shaft and moves along the shaft against the action of a compres-sion spring. The pinion retaining spring is incorporated in the barrel drive.

Rubber Coupling Drives

There are three models of this type, the 'RS' and 'RSB' being for outboard meshing, and the 'RE' for inboard and outboard.

Figure 40. Above, Lucas 'RS' pattern drive.

Figure 41. Above, Lucas 'RSB' pattern drive.

Figure 42. Above, Lucas 'RE' pattern drive.

All these types of drive embody a combination of rubber torsion member and friction clutch. These control the torque transmitted from the starter to the engine flywheel and dissipate the energy developed in the rotating armat-ure of the starter at the moment when the pinion engages with the flywheel.

They also embody an overload release which functions in the case of extreme stress, such as may occur when the starter is inadvertently meshed into a flywheel rotating in the reverse direction.

The 'RS' Type Drive

When the starter is energised, the torque is transmitted to the pinion by two paths. One, from the transmission plate M, Figure 41, which is keyed on to the shaft, via the outer sleeve of the rubber coupling, K, and through the friction washer, H, to the screwed sleeve. The other path: from the transmission plate, M, to the outer sleeve of the rubber coupling, through the rubber to the inner sleeve and then via the centre coupling plate, G, to the screwed sleeve and hence to the pinion. The rubber limits the total torque which the drive transmits and, because the rubber is bonded to the inner sleeve, slipping can only occur be-tween the rubber bush and the outer sleeve of the coupling. This slipping acts as a safety device against overload. Under normal conditions, the rubber will act as a spring and there will be no slip.

Figure 43. Components of the Lucas RS type drive.

In all these drives, a pinion restraining spring D, is fitted, and this prevents the pinion from vibrating into mesh when the engine is running.

This particular drive is the RS pattern, but the principle of operation applies equally well to the other two types, the RSB and the RE.

'RS' Drive – Outboard

Figure 44. Lucas RS drive of outboard type.

This is another picture of the RS drive and you'll notice that it is for outboard meshing.

'RSB' Drive

Figure 45. Lucas RSB type drive.

The RSB drive is again an outboard type. In this drive, a pinion and barrel assembly is used.

'RE' Drive

Figure 46. Lucas RE type drive.

The RE drive is the only one of the rubber coupling types built for both inboard and outboard operation. Again you'll remark that the pinion and barrel assembly is used.

'Eclipse' Drive

The last main group of drives we have to deal with contains the 'Eclipse' pattern. Here you have a general view of this drive, which is used for both inboard and outboard operation.

Figure 47. An example of the Lucas Eclipse type drive.

Basically it is a modified form of the 'RE' drive, a main torsion spring, however, taking the place of the rubber.

'Eclipse' Pattern Drive – Exploded View

A meshing spring 'A' (top left) and friction washer, R, (bottom centre) allow for slip under overload conditions.

Figure 48. Lucas Eclipse drive – exploded view.

The pinion is carried on a barrel type assembly which is mounted on a screwed sleeve, M, (bottom left). This sleeve is carried on a centre sleeve, N, and is secured to the armature shaft by means of a pin and key, P, and O. The barrel assembly is so arranged that it can move along the shaft against the action of the 'torsion' spring, K, to reduce the shock loading at the moment of engagement. A pinion restraining spring, C, is incorporated in the drive.

Pinion Engagement

Before leaving the subject of starter drives, some refer-ence should be made to the difficulties which sometimes arise with starter engagement.

You can be assured that before any engine goes into general production, the engine manufacturer has satis-fied himself that the Lucas starter which he has selected – generally in collaboration with our Sales Engineers – is suitable for that engine.

It sometimes happens however, that the assembly toler-ances for instance, which finally determine the position of the leading edge of the flywheel teeth in relation to the starter motor pinion, do not work out quite as expected, resulting in starting troubles in service. The starter pinion may have to travel too far, thus developing a high speed before engaging the flywheel teeth, with the result that 'milling' or 'chipping' of the teeth takes place.

Comparing A New And Worn Pinion

You can see in this picture how badly the teeth of one of the pinions have been damaged.

Figure 49. Starter pinions, upper is worn, lower is new.

Flywheel Ring – Normal Wear

Figure 50. Flywheel ring gear, showing normal wear.

These flywheel teeth show no more than normal wear after prolonged service.

Out Of Mesh Clearance

If the distance between pinion and flywheel is correct, no abnormal wear of the teeth takes place, the pinion sliding into mesh with little preliminary rotary movement. This distance, when the pinion is in the disengaged position, is called the 'out-of-mesh clearance.

Figure 51. Showing out of mesh clearance, outboard drive.

Figure 52. Showing out of mesh clearance, inboard drive.

In Figures 51 and 52, we show both an outboard and in-board type arrangement here, the difference between measurements, A and B, being in each case the out-of-mesh clearance.

Measuring Out Of Mesh Clearance

The method of measuring the clearance is shown in Figure 53.

First take the dimension in the left hand picture, that is the distance between the starter – flange face and the leading edge of the pinion teeth.

Figure 53. How to measure out of mesh clearance.

Then, as in the picture on the right, measure the distance from the machined face on the clutch housing to the fly-wheel ring gear. A properly calibrated depth gauge should be used to ensure accurate measurement.

The first measurement should then be subtracted from the second.

The correct clearances for the various types of drive are:

Eclipse Type ¹/₁₆" to ³/₁₆"

All other types ³/₃₂" to ⁵/₃₂"

Excessive Armature End Float – Shimming

Even if the clearance was originally correct, if, in the course of service, excessive end-float is allowed to de-velop in the armature shaft, the out-of-mesh clearance may be sufficiently increased to cause trouble.

Figure 54. Shim adjustment of armature.

If noisy starter operation is experienced, the armature end-float of the starter should be checked, and if found to be excessive, shims should be inserted to take up the play. In the case of outboard starters, shims should be inserted at both the commutator and drive ends. In the case of inboard machines, the drive end only is shimmed.

Ten-thousands (0·010) of an inch end float is normal, but if more than 0·015", the out-of-mesh clearance may be affected, and any excess should be taken up.

Faulty Engagement And Disengagement

Faulty engagement as a general rule is the result of allowing the screwed sleeve and pinion assembly to be-come rusty or choked with grease or dirt and this may be easily rectified by a clean-up and re-lubrication with a light machine oil. It is particularly important to use a light machine oil under low temperature operating conditions when the motor's acceleration may be reduced owing to the heavy current taken by the motor.

Other reasons for failure to engage may be broken or distorted restraining springs, broken or contracted main springs, faulty re-assembly of the complete drive after servicing, or incorrect out-of-mesh clearances.

As far as faulty disengagement is concerned, we will con-tent ourselves with listing the likely causes. Sticking of the pinion in mesh with the flywheel can be caused by:

1) Bent armature.

2) Worn screwed sleeve, which causes the pinion to stick along the thread.

3) Dirty or rusty condition of the sleeve and pinion.

4) Slack drive assembly, usually due to the weakening of the compression spring.

5) Incorrectly adjusted switch operating cable.

Assembly And Lubrication Of Drives

These other points should not be overlooked if the mech-anical side of the starting operation is in any way suspect.

Figure 55. Section showing starter motor drive.

First, the assembly of the drive. The unit may have been dismantled and reassembled incorrectly, in which case the best results can hardly be expected. And secondly the drive may be dry or dirty. A clean drive, lightly oiled, will give efficient operation.

PART FOUR – SERVICE TESTING ON VEHICLE

Starter Circuits

Having dealt mainly with the mechanical aspects of starting and starter motors, we shall now discuss the electrical side, showing you various starter circuits and finishing with a comprehensive series of tests for proving the electrical system.

Fundamentally the starter circuit is extremely simple as you can see, consisting of the feed wire from the battery to the starter motor, the circuit being controlled by a switch. The return path is via the chassis.

Figure 56. Diagram of basic starter motor electrical circuit.

Lucas produce several types of starter switch. The one represented here is the simple manually-operated pull or push type.

Manually Operated Starter Switches

Several examples of the manually operated switch are shown here.

Figure 57. Above, right, a selection of Lucas starter motor switches.

Each type, of course, is capable of passing the heavy current required by the starter motor, without voltage loss.

The effective life of any of them depends mainly on two factors: that the contact should be clean and positive; and that the break should be quick, with sufficient travel.

Switch Adjustment

Where the switch is operated by Bowden Cable, it is extremely important that the pull is correctly adjusted. Otherwise excessive burning of the contacts takes place, with resultant loss of starter performance. There is a danger also, that with a too close adjustment of the switch contacts, the starter motor may be vibrated into operat-ion. There should be about ⅛" free movement in the cable before the switch lever is moved. See Figure 58.

The push type switches are spring-loaded and require no adjustment.

Figure 58. A Lucas pull type starter switch.

'G' Type End Bracket

Figure 59. The 'G' type end bracket, showing the contacts.

For starter motors with inbuilt manual switch, where this 'G' type end bracket is used, the two fixed contacts, each with two cheese head screws, must be faced to ensure correct alignment for the moving contact.

End Bracket Blanking Plate

We now mount the starter switch separately, thus enabl-ing us to produce a standard type of end bracket. Many starters with 'G' type end brackets are still, however, in service and for these a 'blanking-off' plate is used which carries a disc contact to bridge the two fixed contacts.

Figure 60. The blanking plate in position on end bracket.

This arrangement enables the separately mounted switch, usually of the solenoid type, to be used.

Starter Solenoid Switch

The electrically operated switch or solenoid is shown here in Figure 61.

It contains the main starter contacts which are closed magnetically when the relay winding inside the switch is energised – that is when the starter push on the dash-board is pressed.

Figure 61. A typical Lucas starter solenoid switch.

One end of this winding is connected to the smallest of the three terminals, and the other end to the metal case, which is earthed when the solenoid is bolted to the metal-work of the vehicle.

Circuit For Solenoid Operated Starter

In the normal circuit, the feed to the solenoid operating push is taken effectively from the ignition switch; A3 on the fuse board being used here only as a junction point. You'll notice there is no fuse in circuit. The cable from the negative of the battery is taken direct to one of the main solenoid terminals, the other main terminal being con-nected to the starter motor. The circuit is again completed via the starter and battery earths.

Figure 62. Circuit diagram for solenoid operated starter.

Testing The Starter System

From the earlier parts of our talk you may have gained the impression that starting troubles are mainly mechan-ical in origin – far from it. Trouble may often be traced to electrical causes: either to a faulty battery, a bad connect-ion in the circuit or to a poor contact at the switch. It should never be assumed when faced with total failure or sluggish operation of a starter motor, that the fault lies necessarily with the motor itself.

It is therefore imperative that a systematic series of checks be first carried out on the electrical circuit so that the fault may be localised.

Checking Procedure

We shall tackle the job in this order:

1) Battery check.

2) Voltage at the Battery.

3) Voltage at the Starter.

4) Voltage drop on main Line.

5) Checking starter switch.

6) Voltage drop on earth Line.

Battery Check – Hydrometer Test

Figure 63. Carrying out the hydrometer test on battery.

The hydrometer should show an evenly charged battery, that is, no great variation in cell readings, and at least a half-charged condition.

Battery Check – Heavy Discharge Test

As a further check for the battery, a heavy discharge tester should be applied for approximately 15 seconds to each cell.

Figure 64. The heavy discharge test on each battery cell.

Steady readings of approximately 1·5-v. per cell indicate a serviceable battery. A falling reading will be obtained from any cell which is defective.

We have thus made sure that the battery is at least cap-able of giving the heavy current required by the starter motor.

Voltage At The Battery Terminals

And now, the rest of the circuit. The first check will give us the working voltage or pressure at the battery. The voltmeter is connected between positive and negative terminals.

When the starter is operated on a cold engine, the readings should not fall below 10-volts for the 12-volt system and 4·5-volts for the 6-volt system.

Figure 65. Checking the voltage at the battery terminals.

Voltage At Starter Motor Terminal

Figure 66. Voltage test at starter motor terminal.

Assuming the voltage at the battery to be in order, next check the voltage at the starter terminal. This should be no more than 0·5-volt lower than the previous reading. The voltmeter is connected between the starter terminal and the starter yoke. In this photograph, the bottom volt-meter lead should NOT be connected where it is – there may be a bad connection between the engine block and the starter yoke (pinion end bracket) itself.

If a low reading had been obtained, both at the battery in the previous test and at the starter terminal, the motor is taking too much current, and the trouble will be found in the starter motor itself.

A good voltage at the battery and a poor voltage at the starter i.e. a considerable voltage drop, indicates a high resistance somewhere in the circuit.

Voltage Drop On The Insulated Line

For our next test, we connect the voltmeter between the starter terminal and the main battery post to check the voltage drop on the insulated or feed line.

Before the starter switch is closed, battery voltage should be registered. But on closing the switch, the reading should fall to zero; but readings of up to 0·5-volt are permissible in service. If a higher voltage is registered, a high resistance point somewhere along the line is indicat-ed. The most likely place is at the switch contacts.

Figure 67. Voltage drop test on the insulated line.

Checking The Switch Contacts

Figure 68. Checking the switch contacts.

The contacts can be checked by connecting a voltmeter across them and closing the switch. The reading of bat-tery voltage should fall immediately to zero or within 0·5-volt of zero.

If the reading is within this limit, the high resistance deduced in the last test must be due either to a loose or corroded terminal, either at the battery or starter switch, or at the starter motor. All of these points can easily be checked by a visual examination.

Voltage On Earth Line

In this last test, we are checking for voltage losses caused by a high resistance point on the earth return side of the circuit.

The voltmeter is connected between the battery earth terminal and the starter yoke. If the earth line is in order, the voltage drop when the starter is operated will be zero.

In service, a voltage drop of 0·5 volt is permissible.

Figure 69. Checking voltage on earth line.

The Earth Connection

If a substantially higher reading is obtained, all earth con-nections in the starter circuit must be checked.

Figure 70. The earth return connection.

Using the voltmeter as we have shown, each connection must be proved electrically sound. The most frequent cause of voltage drop on the earth line is a bad connect-ion where the lug is earthed. Make sure that any such connection is clean and tight. Be particularly wary if the vehicle has just been repaired or painted; the connection may have been disturbed.

The Bonding Strip

Another likely trouble spot is at the 'bonding strip' bet-ween the engine block and the chassis. Remember that modern engines are rubber-mounted, the only good elec-trical connection to the chassis often being made by means of this strip.

Sluggish operation of the starter and sometimes complete failure can be caused by such a fault, or by a combination of minor losses at different points which produce in one circuit a sufficiently serious voltage drop to affect the performance of the starter motor.

We hope we have proved our point: do not suspect the starter before you have tested its electrical supply. Like most of us, it won't work if it's not fed properly.

Figure 71. The bonding strip (earth strap) must be sound.

SUPPLEMENT ONE – THE LUCAS M45G PRE-ENGAGED STARTER

General View – Manually Operated Pre-Engaged Starter

The majority of Lucas starters are equipped with the inertia or 'crash-type' drive. In this arrangement, the starter motor is first energised, the revolving armature then forcing the pinion along a screwed sleeve into mesh with the engine flywheel.

Figure 72. A Lucas pre-engaged starter motor.

The pre-engaged starter we feature here employs a different method of engagement: as its name implies, the pinion is actually in mesh with the flywheel ring gear prior to the torque being applied.

This type of engagement is more suitable for heavier engines of the diesel type, where large flywheels, high compression ratios and generally higher cranking speeds are usual. A normal inertia drive would quickly be dam-aged when operating under these conditions; the mesh-ing impact of the driven-pinion on a comparatively solid flywheel would be far too great to give an adequate service life for the starter motor.

The pre-engaged starter is basically similar to the Standard M45G motor, with a different drive assembly, and a pilot switch.

Cross Section Of Starter And Fly-Wheel

The position of the pilot switch in relation to the drive assembly is visible in Figure 73.

Figure 73. Sectioned view of starter and bell-housing, showing starter operating rod in position.

When the starter operating rod is moved into the starting position, the operating lever attached to the end of it slides the pinion along the armature shaft into mesh with the flywheel ring gear. In Figure 70, the movement is just beginning. When the pinion has travelled the correct dist-ance, the operating lever will close the pilot switch contacts. This completes the circuit for the energising winding of the starter solenoid, thus closing the main starter contacts. The starter armature revolves, transmitting the cranking torque via the pre-engaged pinion to the fly wheel.

The Components Connected In Circuit

Figure 74. The components that make up the circuit.

We have connected the components in circuit here to give a general idea of the layout. Note the pilot switch on the starter motor.

We will assume that the starter pinion has just been pushed into mesh with the flywheel. The pilot switch contacts will thus be made and the circuit for the energising winding of the solenoid completed. Commencing at the battery earth, this circuit is as follows: through the two 6-volt batteries to one of the main solenoid terminals which is connected to one side of the pilot switch. Current passes across the switch contacts to the small solenoid terminal. The energising winding is connected between this terminal and the case which, as you can see, is earthed. The circuit is thus returned to the battery.

When the solenoid operates, the plunger closes the main contacts in the starter supply line, thus energising the starter in the normal way.

The Wiring Circuit

The internal and external connections can be seen from this circuit.

Figure 75. Wiring circuit for a pre-engaged starter motor.

The study of this diagram will be simplified if you divide the circuit into two: first, the relay operating circuit; secondly, the main current circuit.

The Pilot Switch And Rubber Shroud

This close-up shows the pilot switch with its two grub screw connections, at left. The switch plunger is actuated by the operating lever when the starter rod is moved.

Figure 76. The pilot switch and the rubber cover for the pinion engagement mechanism.

The switch assembly is fixed to the starter body by four set screws, which also serve to fasten the water-proofing rubber shroud in position.

The switch bracket is slotted so as to allow adjustment of the switch in relation to the operating lever. We shall be referring to this adjustment more fully later on.

The Armature Brake

Let us now make a more detailed examination of the mechanical operation of this starter.

In the rest position, the bottom of the operating lever holds a brake plate hard against a brake lining. You can see the coiled springs which provide the tension. The plate is carried on the splines of the armature shaft and the brake lining riveted to the intermediate bracket. The armature is thus prevented from rotating when the plate and lining come into contact.

Figure 77. Sectioned view of the armature brake system.

Consider for instance a case where the starter is oper-ated and the engine fires, but then stops; the starter pinion could possibly still be revolving when it was again meshed into the flywheel. The coiled springs prevent this by returning the operating lever to the rest position and in so doing, a braking effect is applied to the armature.

The Operating Lever

Figure 78. The operating lever.

The stirrup shaped end of the operating lever is visible here so are the coiled springs holding it under tension. The two toggles actually form the bearing member that acts on the brake plate.

The Brake Lining And Brake Plate

And here you see, on the left, the brake lining attached to the starter intermediate bracket.

Figure 79. Components that make up the armature brake.

On the right, we have photographed the brake plate in position at the end of the drive assembly.

The Compression Spring

The next feature of the drive assembly we wish to discuss is the compression spring. This is situated immediately behind the pinion and barrel assembly.

Figure 80. The location of the compression spring.

Usually, the pinion and flywheel mesh without any difficulty, the teeth being chamfered at the leading edges to ease the engagement. It can happen however that the teeth butt against one another – this is known generally as 'tooth to tooth' engagement. When this occurs, the pinion will not slide into mesh but remains tight against the flywheel teeth. Increased pressure must be applied to the starter operating rod. This compresses the heavy spring behind the pinion and barrel, the compression continuing until the pilot switch contacts are closed by the operating lever. The spring can be more clearly seen in the exploded view in Figure 81. The armature then begins to turn and immediately the pinion is sprung into mesh.

The Clutch

A clutch mechanism is incorporated in the drive to avoid overloading the starter. It is housed in the barrel of the pinion and barrel assembly.

Immediately the armature begins to turn, a heavy steel ring slides along a fast thread compressing the clutch plates and transmitting the drive to the pinion and barrel.

Figure 81. The components that make up the clutch.

If the pinion sticks in mesh and the flywheel attempts to drive the starter motor, the steel compression ring returns along the fast thread to the rest position, leaving the clutch plates slack so that no drive can be transmitted through them.

If, to take another case, the engine load is too great, such as when the vehicle is in gear and the starter motor attempts to turn over the engine, the clutch is arranged to slip, thus relieving any abnormal strain on the motor. This slipping will also protect the starter should the engine backfire. The clutch is set during manufacture to slip in the driving direction at two to three times the normal full load torque and should never normally need re-adjust-ment in service.

Pilot Switch Adjustment

You will appreciate that the position at which the operat-ing lever closes the switch contacts is rather critical if the pinion engagement is to be trouble free. Provision is therefore made for adjusting the position of the switch plunger with respect to this lever.

Figure 82. Location of pilot switch adjustment screws.

The four set screws, visible in the picture secure the cover plate and at the same time lock the adjusted switch in position.

The Adjusting Holes

This shows the elongated adjusting holes when the cover has been removed.

Figure 83. Elongated holes in pilot switch mount plate.

Procedure For Adjusting Switch

In service, the adjustment of the switch should be carried out with the starter motor removed from the vehicle.

The pilot switch should then be set to make electrical contact when the leading edge of the starter pinion is from 1⅝" to 1¾", as specified for individual vehicles, from the machined face of the drive end bracket. The switch fixing screws should be temporarily loosened and the operating lever pressed until the correct distance is reached. The switch can then be moved forward so that the plunger engages with the operating lever.

We suggest that a test lamp and battery be connected in series with the switch so as to facilitate finding the exact position at which the plunger closes the contacts.

Figure 84. Adjusting the pilot switch using pinion position.

When the motor is re-fitted, care must be taken to see that the starter operating linkage on the vehicle is correct-ly adjusted. There should be no slack in the movement; on the other hand, full travel of the operating lever must be assured.

Maintenance

The pre-engaged starter needs no further attention in service beyond that given to normal starter motors.

An inspection of the brush gear and commutator, together with a check of the external electrical connections and cabling, should form part of the normal maintenance.

Document Restorer's Note

Some of the electrical system tests can be carried out with a multi-meter set to 'Continuity'. If a multi-meter is used, be sure that the currents are not excessive.

In the diagnostic section, on Page 24, mention is made of the 'Bonding Strip'. This component is now commonly identified as an 'Earth Strap' – it is, emphatically, one of the most important components in a vehicle's wiring system. Sound contact between the engine block and the body/chassis structure is essential. Low quality earthing contacts at this point can, on engagement of the starter, be the cause choke and throttle cables to glow red hot, and could start outbreaks of fire.