Franzis Pe01 User manual

PORSCHE 911PORSCHE 911

Flat-Six Boxer

engine

Instruction

MANUAL

10+

For Ages

Build your own

working, classic

Porsche 911

flat-six engine

model!

Mehr Franzis-Produkte im Internet www.franzis.de

FRANZIS Verlag GmbH

D-85540 Haar bei Munchen

Germany

Item number:

PE01

Trends UK LTD, Greatworth Hall,

Banbury, OX17 2DH. UK

Email: [email protected]

Customer services:

+44 (0)1702 208175

INTRODUCTION ...................................................2

NOTES AND ADVICE............................................6

PARTS LIST .........................................................7

ASSEMBLING THE ENGINE...............................15

Step 1. Pistons.....................................................15

Step 2. Crankshaft................................................15

Step 3. Crankshaft drive gear................................15

Step 4. Crankshaft assembly ................................16

Step 5. Cylinder barrels........................................16

Step 6. Crankcase rear .........................................17

Step 7. Crankcase assembly.................................17

Step 8. Valve guides ............................................18

Step 9. Valve assembly........................................18

Step 10. Oil cooler...............................................19

Step 11. Cylinder head – right side ......................19

Step 12. Camshaft tunnel – right rear ...................20

Step 13. Cam and rocker shafts – right side .........20

Step 14. Camshaft assembly – right side..............21

Step 15. Rocker shaft assembly – right side .........22

Step 16. Cylinder head – left side ........................23

Step 17. Timing pin .............................................24

Step 18. Crankshaft sprocket................................24

Step 19. Valve timing tool ....................................25

Step 20. Cam belt – left side................................25

Step 21. Cam belt cover – left side ......................26

Step 22. Distributor drive gears............................26

Step 23. Cam drive sprocket – right side..............27

Step 24. Cam belt – right side..............................27

Step 25. Cam belt cover – right side ....................28

Step 26. Distributor..............................................28

Step 27. Engine front ...........................................29

Step 28 Crankshaft pulley wheel...........................29

Step 29. Drive motor............................................30

Step 30. Cylinder head covers..............................30

Step 31. Exhaust manifolds ..................................31

Step 32. Exhaust pipes.........................................31

Step 33. Exhaust muffler ......................................32

Step 34. Base - battery installation .......................34

Step 35. Base label..............................................35

Step 36. Base ......................................................36

Step 37. Cooling fan assembly.............................34

Step 38. Cooling fan installation...........................34

Step 39. Spark plugs............................................35

Step 40. Carburettors...........................................36

Step 41. Operation...............................................36

HOW AN ENGINE WORKS.................................37

PE01 Porsche Flat-Six Boxer Engine

publication may be reproduced, stored in a

retrieval system or transmitted, in any form

or by any means, electronic, mechanical,

photocopying, recording or otherwise,

without prior permission in writing from the

publisher.

Printed in China

Please retain the information in

this manual for future reference.

This device complies with Part 15 of the FCC Rules. Operation is subject to

the following two conditions:

(1) this device may not cause harmful interference

(2) this device must accept any interference received,

including interference that may cause undesired operation.

Caution: Changes or modifications not expressly approved by the party responsible

for compliance could void the user’s authority to operate the equipment.

Note: This equipment has been tested and found to comply with the limits for a Class

B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to

provide reasonable protection against harmful interference in a residential

installation. This equipment generates, uses and can radiate radio frequency energy

and, if not installed and used in accordance with the instructions, may cause harmful

interference to radio communications. However, there is no guarantee that

interference will not occur in a particular installation. If this equipment does cause

harmful interference to radio or television reception, which can be determined by

turning the equipment off and on, the user is encouraged to try to correct the

interference by one or more of the following measures:

- Reorient or relocate the receiving antenna.

- Increase the separation between the equipment and receiver.

- Connect the equipment into an outlet on a circuit different from that to which

the receiver is connected.

- Consult the dealer or an experienced radio/TV technician for help.

Flat-Six Boxer Engine

Build your own working, classic Porsche 911 flat-six engine model!

Contents

PORSCHE 911

The car that was to become the Porsche 911 was first unveiled at

the 1963 Frankfurt motor show, intended as a larger, more

comfortable, successor to the legendary 356. As well as a new

chassis and suspension, a completely new, six cylinder, overhead

cam boxer engine was designed (called the Type 901), to replace

the four cylinder, overhead valve unit used in the 356. Design of

the new engine was led by Hans Mezger, a German automotive

engine who became a key part of Porsche’s development

programme for 35 years.

The primary reason for using the new 6-cylinder engine was to

utilise the inherent smoothness offered by the boxer configuration.

Because it consisted of three pairs of pistons moving backwards

and forwards in opposite directions, with each pair spaced at 120

degrees of crankshaft rotation, the design minimised first and

second order vibrations (vibrations that occur once and twice per

engine revolution). In addition, the short length of the engine, low

centre of gravity, and effectiveness of air cooling made it ideal for

the rear-engine 911.

To meet the high bending stresses at very high revolutions, the

forged crankshaft was supported with eight main bearings.

The crankcase was split vertically, and like all of the major

components, was made from aluminium (even the cooling fins of

the cylinders were aluminium, with cast iron sleeves inside them).

Each row of three cylinders had an overhead camshaft, these

being driven by a duplex chain running around intermediate gears

on a layshaft (itself gear driven from the crankshaft). Accurate

valve timing and smooth operation were achieved by using a

hydraulic cam chain tensioning wheel and rubber guide ramps.

The valves were arranged in a V-shape, which allowed the use of a

hemispherical combustion chamber with a small, smooth and

heat-absorbing surface. Initial versions of the engine used Solex

overflow-type carburettors, and although these had the benefit of

being relatively insensitive to forces caused by hard cornering,

problems with these, including a flat spot at low engine speeds,

led to them being changed for Weber carburettors in 1966.

INTRODUCTION

4 5

An 11 bladed axial fan,

with the alternator inside it,

was mounted on top of the

engine to improve cooling

by helping to ensure the

air was more evenly

distributed to both sets of

cylinders.

In its original form (Type

901/01), the engine had a

capacity of 1,991 cubic

centimetres, with a

cylinder bore of 80 mm

and a stroke of 66 mm.

Power output was 130 hp (96 kW) at 6,100 rpm. Subsequent

developments led to the 901/02, 901/03 and other versions,

each having different specifications depending on the intended

use (sports, touring etc). The Carrera six engine (Type 906) was

developed simultaneously to the Type 901, the main differences

being the use of twin spark plugs per cylinder,

higher-compression pistons, and the use of lighter weight

(magnesium and titanium) components. A major change came

in 1970, with the capacity of the engine being increased to

2,200 cubic centimetres (2.2 litres) by increasing the bore to 84

mm. The original engine configuration was still being used until

1972, when it was superseded by the even larger 2,341 cubic

centimetre engine.

The model in this kit is intended as representation of the Type

901 engine used in the early 911. Although it lacks the fine

details of the real engine, it includes a realistic crankshaft, a

working cooling fan, and accurate valve and ignition timing.

Even the distributor works correctly, being driven from the

crankshaft using bevel gears, with its red colour closely

matched to the real thing.

An early Porsche 911 engine, with cut-away sections to show the internal

components. The engine shown is part of the Porsche museum collection

in Stuttgart.

No. Description Qty

1 Connecting rod 6

2 Piston half 12

Cams (labelled A – F) 6

4 Bearing cap 6

5 Rocker arm 6

6 Timing tool 1

7 Valve stem 6

9 Valves 12

10 Crankshaft sprocket A 1

11 Crankshaft sprocket B 1

12 Camshaft sprocket 2

13 Gudgeon (piston) pin 6

15 Carburettor outer 2

16 Carburettor inner 2

19 Exhaust muffler upper 1

20 Exhaust muffler lower 1

21 Exhaust pipe left upper 1

22 Exhaust pipe left lower 1

23 Exhaust pipe right upper 1

24 Exhaust pipe right lower 1

25 Crankshaft pulley 1

26 Fan pulley 1

27 Oil return pipes 4

28 Exhaust manifold left upper 1

29 Exhaust manifold left lower 1

30 Exhaust manifold right upper 1

31 Exhaust manifold right lower 1

32 Oil cooler outer 1

33 Oil cooler inner 1

34 Fan housing 1

37 Idler pulley 2

41 Crankshaft 1

42 Cooling fan 1

No. Description Qty

47 Crankcase upper 1

48 Crankcase lower 1

49 Cylinder barrels 2

50 Cylinder head left 1

51 Cylinder head right 1

52 Upper cylinder head left 1

53 Upper cylinder head right 1

54 Large cylinder head plate 2

55 Small cylinder head plate 2

56 Crankcase rear 1

57 Cylinder head plate upper 2

58 Cylinder head plate lower 2

59 Cam belt tunnel left inner 1

60 Cam belt tunnel right inner 1

61 Cam belt tunnel left outer 1

62 Cam belt tunnel right outer 1

63 Cam belt tunnel middle 1

67 Drive gear 1

68 Crankshaft gear 1

69 Distributor gear 1

Cam timing belt 2

72 Spark plug lead mounting clip 1

74 Distributor bushing 1

75 Crankshaft gear B 1

76 Crankshaft gear C 1

77 Timing alignment pin 2

78 Fan housing rear cover 1

Valve spring 12

Cam shaft (140 mm) 2

Rocker shaft (118 mm) 4

Metal shaft (37 mm) 1

Head gasket 2

Base 1

Distributor/spark plug assembly 1

Label 1

References to the left or right side of the engine mean the left or right side when

viewed from the fan end. Cylinders 1-3 are on the left side of the engine and

cylinders 4-6 are on the right.

Identify the various parts by looking at the list of components and the

corresponding illustrations. Use a sharp knife to trim any excess plastic from the

components after they have been removed from their carrier frames.

Take care not to over-tighten the screws as this may permanently damage the

plastic.

- Non-rechargeable batteries are not to be recharged.

- Rechargeable batteries are only to be charged under adult supervision.

- Rechargeable batteries are to be removed from the toy before being charged.

- Do not mix old and new batteries.

- Do not mix alkaline, standard (carbon-zinc), or rechargeable (nickel-cadmium)

batteries.

- Batteries are to be inserted with the correct polarity.

- Exhausted batteries are to be removed from the toy.

- The supply terminals are not to be shorted-circuited.

NOTES AND ADVICE PARTS LIST

6 7

PARTS LIST PARTS LIST

8 9

PARTS LIST PARTS LIST

10 11

19 Muffler upper

20 Muffler lower

25 Crankshaft

pulley

34 Fan

housing

42 Cooling

fan

47 Crankcase upper

48 Crankcase lower

49 Cylinder barrels

37 Idler

pulley

37 mm

shaft

41 Crankshaft

26 Fan pulley

27 Oil return pipes

50 & 51

Cylinder heads

PARTS LIST PARTS LIST

12 13

67 Drive gear

68 Crankshaft

gear

69 Distributor

gear

76 Crankshaft

gear C

Distributor

bush

75 Crankshaft

gear B

Base

Distributor and

plugs

Motor assembly

Rocker and cam shafts

Valve spring

Fan belt

Head gasket

Timing belts

78 Fan

housing

rear cover

52 & 53 Upper cylinder head

PARTS LIST ASSEMBLING THE ENGINE

14 15

Step 1. Pistons

Push a gudgeon (piston) pin (13) through the

small end of a connecting rod (1). Push two

halves of a piston (2) together over the pin and

press together firmly.

Repeat for the other five piston/rod assemblies.

Step 2. Crankshaft

The six connecting rods attach to the

crankshaft (41) in the positions shown.

In each case, place the connecting rod over the

crankshaft, fit a bearing cap (4) and secure with

two screws.

Check that the piston/connecting rod

assemblies rotate freely around the crankshaft.

Step 3. Crankshaft

drive gear

Fit the crankshaft drive gear (68)

to the end of the crankshaft.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

16 17

Step 6. Crankcase rear

Slide the crankcase rear

(56) in to the upper

crankcase. There is a

rib in the plate that fits

into a corresponding

slot in the upper

crankcase - refer to

the inset image (the

crankshaft and drive

gear have been

removed for clarity).

Step 7. Crankcase assembly

Fit the lower crankcase (48)

to the upper crankcase and

secure with seven screws.

Step 4. Crankshaft

assembly

Place the upper crankcase

(47) upside down on a table.

Hold the piston/crankshaft assembly,

and lower it on to the crankcase.

Step 5. Cylinder barrels

Attach the cylinder barrels (49) to the upper

crankcase. Carefully slide the pistons into each

set of barrels and then lower the barrels into the

crankcase. Ensure the barrels are the right

way up - note that the barrel for the

middle piston has a rib that fits into

a corresponding slot in the upper

crankcase.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

18 19

Step 10. Oil cooler

The oil cooler must be fitted at

this time. This is in two parts

(32 & 33), and should be

assembled so that the parts

clamp to the T-shaped

moulding on the side of the

crankcase. Hold the smaller

inner part (33) in place, then fit

the larger outer part of the

cooler (32) to this and secure

with two screws.

Step 11. Cylinder head –

right side

Place a paper cylinder head gasket over the

right hand cylinder barrels. Fit two oil return

pipes (27) to the moulded lugs on the side of

the crankcase, then fit the right cylinder head

(51) and secure with four screws.

Repeat for the other (left)

side of the engine, using

the other gasket, two oil

return pipes, and the left

cylinder head (50).

Step 8. Valve guides

Fit two valve guide plates to

each of the lower cylinder

heads. Note that each head

uses one narrow plate (55)

and one wide plate (54).

Each plate has three round

studs that face downwards

into the head. First fit the

tabs on the outside of

each plate into the

corresponding holes

in the side of the

head, then push the

plates down firmly

so they clip into

position (circled).

Step 9. Valve assembly

For each cylinder head, you will need six valves (9),

valve stems (7) and valve springs. Fit to the head as

shown. First slide a spring over a valve stem, and

insert into one of the six holes in the valve guide plates.

Gently compress the spring until the end of the stem

sticks out of the bottom of the head. Carefully push the

valve on to the stem. Note that the end of the valve has

a step – push the valve until it touches the edge of the

step. DO NOT force the valve – these parts are

delicate.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

20 21

Step 13. continued

Slide three rocker arms (5) on to each

of the two rocker shafts, checking

that they move freely.

Note the relative position of the inlet (top)

and exhaust rockers (bottom).

Step 14. Camshaft assembly –

right side

Place the camshaft assembly in position on the

cylinder head. This is easiest if the engine is

held on its side between your legs, with the

cylinder head horizontal. Ensure that the cams

are separated so that each sits between the

bearing surfaces in the head.

Step 12. Camshaft

tunnel – right rear

Attach the rear part of the right

hand camshaft tunnel (60) to

the crankcase and secure with

two screws.

Step 13. Cam and rocker

shafts – right side

Assemble the camshaft for the right side of

the engine. Slide cams D, E, and F on to a

camshaft, IN THIS ORDER.

Note that the hole in each cam has a flat

surface, which ensures that each one is

correctly positioned on the shaft. Also note

that there is a rib at one end of each cam.

IMPORTANT! To ensure correct valve timing,

the cams must all be fitted with the rib

pointing to the REAR of the engine (direction

of arrow in diagram below).

Fit the sprocket to the end of the camshaft –

the hole in this also has a flat surface to

ensure it is correctly positioned.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

22 23

Step 16. Cylinder head –

left side

Repeat steps 11 to 14 for the left hand side of

the engine. Note the position of cams A, B and

C, making sure the ribs on each point towards

the rear of the engine.

Step 15. Rocker shaft

assembly – right side

Place the rocker shaft assemblies for the inlet

and exhaust valves on to the cylinder head

(refer to the inset picture for guidance). Use

your fingers to separate the rockers so that

each sits between the bearings that hold the

shaft. The ends of each rocker shaft should be

level with the end of the cylinder head.

Place the cylinder head cover (53) in position.

Note the correct orientation - the two tubes

moulded into the bottom edge should be

inserted into the ends of the oil return pipes.

Secure with six screws.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

24 25

Step 19. Valve timing tool

Fit the valve timing tool (6) to

the left hand side of the engine.

There are two pins at one end

that fit into the holes in the

sprocket beneath the

crankshaft, and three at the

other end that fit into holes in

the camshaft sprocket.

Step 20. Cam belt – left side

Remove the timing alignment

pin as shown (but do not

remove the one in the lower

sprocket). Place one of the

cam timing belts in position

over the cam and drive

sprockets. Install the idler

pulley (37), making sure the

cam belt goes up and

over this.

Step 17. Timing pin

In order to accurately set the valve and ignition

timing, the crankshaft must be locked into

position. Note that the pistons in cylinders

1 and 4 must be at Top Dead

Centre (TDC). Insert a timing

alignment pin (77) through the

holes in the crankcase and

crankshaft counterweight.

Insert the metal shaft for the

cam chain sprocket into the

crankcase.

Step 18. Crankshaft sprocket

Slide the crankshaft gear B (75) on to the end

of the crankshaft. Note that there is a slot in the

inside surface of the sprocket that engages

with a rib on the crankshaft.

Fit the crankshaft sprocket A

(10) to the metal shaft. Note

that the shaft has a flat surface

on one side that matches a flat

surface on the inside of the

sprocket. IMPORTANT! There

is a hole on one side of the

sprocket through which the

second timing alignment pin

(77) must be inserted to fit into

a hole in the crankcase. This

ensures that the sprocket is

correctly aligned. You may

need to reposition the sprocket

to allow the pin to be inserted.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

26 27

Step 23. Cam drive sprocket –

right side

Fit the crankshaft sprocket B (11) to the metal

pin, followed by the valve timing tool.

Step 24. Cam belt – right side

Install the second cam belt and idler pulley.

Step 21. Cam belt cover –

left side

Remove the valve timing tool,

and the timing alignment pin

from the lower sprocket.

Fit the cam belt tunnel cover

(61) and secure with three

screws.

Step 22. Distributor drive gears

Install the distributor drive bevel gears. Fit the

smaller crankshaft gear C (76) first - it has a slot

that engages with the rib on the crankshaft.

When fitting the larger gear (69), note the round

groove in one side. To achieve correct ignition

timing, this gear MUST be installed with the flat

section facing downwards as shown. Slide a

timing pin under the gear and into the bracket

in the front of the crankcase to ensure the gear

is correctly positioned.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

28 29

Step 27. Engine front

Attach the engine cover plate

and secure with three screws.

Step 28 Crankshaft

pulley wheel

Fit the pulley to the end of the

crankshaft and secure with

a screw.

Step 25. Cam belt cover –

right side

Remove the valve timing tool

and the bevel gear locking pin.

Place the right hand cam belt

cover in position and secure

with three screws.

Step 26. Distributor

Fit the distributor bush (74) to the end of the

shaft and secure with a screw. One end of the

bush has a recess for the screw; this must face

outwards, as shown.

Fit the distributor – it is a friction fit in the

crankcase. The flat surface on the distributor

shaft and bush match the flat surfaces

of the crankcase and bevel

gear. The bevel drive gear for

the distributor MUST be in the

correct position in order for the

distributor shaft to be fully

inserted.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

30 31

Step 31. Exhaust manifolds

Each exhaust manifold is made up from two

parts. Assemble the upper (30) and lower

(31) halves of the right manifold and secure

with four screws. Fit the assembled manifold

to the underside of the cylinder head and

secure with three screws. Repeat for the left

hand side, using parts (28) and (29).

Step 32. Exhaust pipes

Each set of exhaust pipes is also made up from

two parts. Assemble the upper (23) and lower

(24) halves of the right exhaust and secure with

one screw. Fit the assembled exhaust to the

manifold and secure with three screws. Repeat

for the left hand side, using parts (21) and (22).

Step 29. Drive motor

Fit the drive gear (67) to the

motor shaft. One side of the

gear is recessed; make sure

the recess is facing outwards,

and secure using one of the

metal washers and a screw.

Insert the motor/gearbox

assembly into the hole in the

lower part of the crankcase

and secure with three screws.

Step 30. Cylinder head covers

Attach the upper (57) and lower cylinder (58)

head covers, securing each with six screws.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

32 33

Step 34. Base - battery

installation

Remove the battery compartment cover. Insert

3 x AA batteries in the compartment, taking

care to ensure that the battery markings

(polarity) match the markings in the

compartment. Replace the battery cover.

Step 33. Exhaust muffler

Assemble the two halves of the exhaust muffler

(19 & 20) and secure with four screws.

Slide the muffler over the ends of the exhaust

pipes. The muffler is secured to each exhaust

pipe with a single screw, and to the crankcase

with two screws.

Step 35. Base label

Remove the foil label from the backing paper

and place in position on the base.

Step 36. Base

Attach the base to the bottom of the crankcase

and secure with four screws.

ASSEMBLING THE ENGINE ASSEMBLING THE ENGINE

34 35

Step 39. Spark

plugs

Insert the spark plugs into

the holes in the upper part of

the cylinder heads. Carefully

note the markings on the top

of the distributor cap; follow

the wire that exits from hole

#1 and insert it into cylinder

number 1 as shown. Repeat

for wires/cylinders 2, 3, 4, 5

and 6.

Use the clip (72) provided to

secure the wires for cylinders

4, 5 and 6 so they are routed

neatly over the cooling fan.

Step 37. Cooling fan

assembly

Assemble the cooling fan components

as shown. Attach the rear cover (78) to

the fan housing (34) first, and secure with

two screws. Slide the fan (42) over the shaft,

followed by the fan pulley (26). Secure the

pulley to the fan using a screw and washer.

Check that the fan spins freely; if necessary,

loosen the screw slightly.

Step 38. Cooling fan

installation

Insert the clip on the bottom of

the cooling fan assembly into

the slot in the crankcase.

Fit the fan drive belt – this fits

over the crankcase pulley

and the fan pulley.

ASSEMBLING THE ENGINE

36 37

Step 40. Carburettors

Each set of carburettors is in

two halves (15 & 16). Fit each

pair together and secure with

four screws. Place each in

position over the three inlet

pipes on the top of the cylinder

heads.

Step 41. Operation

Insert the two electrical plugs into the base -

they are two different sizes, and will only fit one

way.

Press the on/off button on the

base to begin operating the

engine. It will continue to run

for 30 seconds and then stop

automatically. Press the on/off

button while the engine

is running to stop it

before the end of the

30 second cycle. Pressing

the button again will start

another 30 second cycle.

HOW AN ENGINE WORKS

Basic Principles

To explain how a full-size car engine works, we’ll use a simplified version of a real engine -

our model engine in fact. You can switch on your finished model as you read this

explanation and it will help you to understand how a real engine works.

An engine crankshaft is described as such because it is a ‘cranked’ shaft – the shaft has

offset sections, to which the six piston/connecting rod assemblies are connected. In the

model, as the crankshaft turns (driven by the electric motor), the cranked sections move

around the centreline of the crankshaft, and convert the rotation to the reciprocating (up

and down) movement of the pistons. In a real engine, it is the movement of the pistons

(driven by the burning of fuel in the cylinders) that causes the crankshaft to rotate.

The engine’s crankshaft drives the transmission, which includes various different

components connected together whose job it is to drive the car’s wheels, making the

car move.

Now let’s look at how the engine works in more detail. We’ll look at just one cylinder of the

engine. A cylinder is the hollow cylinder inside the engine in which one piston moves up and

down. The piston has seals, called piston rings, around its edge, which aren’t shown on our

model and these seals stop gases passing round the sides of the piston. Our model has

six cylinders.

When you turn the engine to start the car, the starter (a powerful electric motor, powered by

the car’s battery) turns the crankshaft, moving the pistons up and down.

As a piston moves down from its highest position inside the cylinder (called ‘Top Dead

Centre’ or ‘TDC’), a mixture of fuel and air is sucked into the space inside the cylinder

above the piston. This is called the intake stroke.

The starter continues to turn the crankshaft and, as the piston moves back up towards the

top of its cylinder, the fuel/air mixture is compressed (squashed) in the space above the

piston. This is called the compression stroke.

As the piston reaches its highest point, a spark plug creates a spark above the piston and

this spark ignites the fuel/air mixture, causing a small controlled explosion above the piston.

The explosion pushes the piston downwards and this is called the power stroke.

Once the piston has reached its lowest point, it starts to move back up its cylinder, pushing

the burnt gases out through the top of the cylinder. This is called the exhaust stroke.

So, the engine has four strokes; intake, compression, power and exhaust, or ‘suck’,

‘squeeze’, ‘bang’ and ‘blow’ to make it simpler. These four strokes make up the

4-stoke cycle.

The fuel/air mixture flows into the space above the piston, called the combustion chamber.

The mixture flows in through a small hole which is opened and closed by the inlet valve.

The burnt gas flows out of the cylinder through another hole which is opened and closed by

the exhaust valve. The valves are normally held closed by springs, but as the engine turns the

valves are pushed open in the correct order by the rocker arms, which are moved by the

camshaft. The rocker arm pushes the valve down against its spring and, as the rocker moves

up, the spring pushes the valve closed.

HOW AN ENGINE WORKS HOW AN ENGINE WORKS

38 39