Mg Mga twin cam Instruction manual

NOTE

Refer to the end of the appropriate Section for the latest instructions when carrying out work on the

vehicle.

Additional copies of this publication (Part No. AKD926B) can only be obtained from an M.G.

Distributor.

Issued by

THE M.G. CAR COMPANY LIMITED

Proprietors: Morris Motors Limited

ABINGDON-ON-THAMES

Exported by

NUFFIELD EXPORTS LIMITED

Proprietors: Morris Motors Limited

COWLEY, OXFORD, ENGLAND

INTRODUCTION

This Manual has been prepared to provide the service operator with the necessary information for

the maintenance and repair of the M.G. (Series MGA Twin Cam).

The Manual also serves as a ready-reference book for service supervision and covers items of

procedure for the guidance of both the fully qualified and the less-experienced mechanic.

UNIT ARRANGEMENT

In the Manual the complete vehicle is divided into Sections each of which deals with an assembly

or major component and carries a reference letter.

NUMBERING OF PAGES AND ILLUSTRATIONS

The pages and illustrations are numbered consecutively within each Section

SERVICE TOOLS

Use of the correct tools contributes to an efficient, economic, and profitable repair. References

have therefore been made to such tools throughout the Manual.

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CONTENTS 
INTRODUCTION .................................................................................................................................................3 
GENERAL INFORMATION
 ................................................................................................................................ 12 
PART NAME ALTERNATIVES .......................................................................................................................................... 23 
MAINTENANCE ATTENTION.......................................................................................................................... 28 
SECTION A THE ENGINE................................................................................................................................36 
GENERAL DESCRIPTION ................................................................................................................................................ 36 
LUBRICATION SYSTEM .................................................................................................................................................. 36 
A.1 DRAINING THE SUMP.............................................................................................................................................. 36 
A.2 OIL PRESSURE ......................................................................................................................................................... 37 
A.3 OIL PRESSURE RELIEF VALVE................................................................................................................................... 37 
A.4 WATER PUMP ......................................................................................................................................................... 37 
A.5 CARBURETTERS ...................................................................................................................................................... 37 
A.6 INLET MANIFOLD .................................................................................................................................................... 38 
A.7 HEADER TANK......................................................................................................................................................... 39 
A.8 THERMOSTAT HOUSING......................................................................................................................................... 39 
A.9 EXHAUST MANIFOLDS ............................................................................................................................................ 39 
A.10 CAMSHAFT DRIVING SPROCKETS.......................................................................................................................... 39 
(TRANSVERSE SECTION)THE M.G. SERIES MGA (TWIN CAM)ENGINE .................................................................................... 41 
A.11 CAMSHAFTS.......................................................................................................................................................... 41 
A.12 CAMSHAFT BEARINGS .......................................................................................................................................... 42 
A.13 CYLINDER HEAD .................................................................................................................................................... 42 
A.14 DECARBONIZING .................................................................................................................................................. 43 
A.15 VALVES ................................................................................................................................................................. 43 
A.16 VALVE GUIDES ...................................................................................................................................................... 43 
A.17 VALVES AND SEATINGS......................................................................................................................................... 44 
A.18 TAPPET CLEARANCES............................................................................................................................................ 45 
A.19 VALVE TIMING-CHECKING AND ADJUSTING ......................................................................................................... 46 
A.20 TIMING CHAIN-ADJUSTING .................................................................................................................................. 50 
A.21 TIMING CHAIN COVER .......................................................................................................................................... 51 
A.22 TIMING CHAIN ...................................................................................................................................................... 52 
A.23 ENGINE FRONT PLATE........................................................................................................................................... 53 
A.24 POWER UNIT......................................................................................................................................................... 53 
A.25 SUMP AND OIL PUMP STRAINER .......................................................................................................................... 54 
A.26 MAIN AND BIG-END BEARINGS............................................................................................................................. 54 
A.27 PISTONS AND CONNECTING RODS ....................................................................................................................... 55 
A.28 PISTON RINGS....................................................................................................................................................... 56 
A.29 HALF-SPEED SHAFT............................................................................................................................................... 57 
A.30 DISTRIBUTOR DRIVE GEAR.................................................................................................................................... 57 
A.31 OIL PUMP.............................................................................................................................................................. 58 
A.32 FLYWHEEL............................................................................................................................................................. 58 
A.33 CRANKSHAFT ........................................................................................................................................................ 59 
A.34 CAMSHAFT LOCKING TOOL................................................................................................................................... 59 
A.35 FLYWHEEL STARTER RINGS................................................................................................................................... 59 
A.36 CONNECTING ROD ASSEMBLIES ........................................................................................................................... 59 
A.37 MODIFIED ENGINE MOUNTING............................................................................................................................ 60 

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A.38 MODIFIED HALF-SPEED SHAFT AND OIL PUMP DRIVING SPINDLE........................................................................ 61 
A.39 MODIFIED PISTONS AND RINGS............................................................................................................................ 61 
A.40 MODIFIED CRANKCASE BREATHER PIPE ............................................................................................................... 61 
A.41 MODIFIED TAPPETS .............................................................................................................................................. 61 
A.42 MODIFIED TIMING COVER GASKET....................................................................................................................... 61 
A.43 ALTERNATIVE PISTONS ......................................................................................................................................... 61 
SERVICE TOOLS ............................................................................................................................................................. 62 
SECTION B THE IGNITION SYSTEM............................................................................................................. 68 
DESCRIPTION ................................................................................................................................................................ 68 
B.1 LOCATING THE CAUSE OF UNEVEN FIRING ............................................................................................................. 68 
B.2 TESTING THE LOW-TENSION CIRCUIT ..................................................................................................................... 68 
B.3 LOCATING ALOW-TENSION CIRCUIT FAULT ........................................................................................................... 69 
B.4 HIGH-TENSION CABLES........................................................................................................................................... 70 
B.5 CONTACT BREAKER................................................................................................................................................. 70 
B.6 REMOVING AND REPLACING THE DISTRIBUTOR..................................................................................................... 71 
B.7 STATIC IGNITION TIMING........................................................................................................................................ 71 
B.8 DISMANTLING THE DISTRIBUTOR ........................................................................................................................... 74 
B.9 CAPACITOR ............................................................................................................................................................. 74 
B.10 REASSEMBLING THE DISTRIBUTOR ....................................................................................................................... 74 
B.11 COIL ...................................................................................................................................................................... 75 
B.12 SPARKING PLUGS .................................................................................................................................................. 75 
B.13 NEW-TYPE DISTRIBUTOR ...................................................................................................................................... 77 
B.14 CHECKING DISTRIBUTOR DRIVE SHAFT BACKLASH ............................................................................................... 77 
B.15 CHECKING THE IGNITION TIMING ......................................................................................................................... 79 
B.16 NEW-TYPE DISTRIBUTOR ...................................................................................................................................... 79 
SECTION C THE COOLING SYSTEM............................................................................................................ 80 
DESCRIPTION ................................................................................................................................................................ 80 
C.1 REMOVING THE FILLER CAP .................................................................................................................................... 80 
C.2 DRAINING THE COOLING SYSTEM........................................................................................................................... 80 
C3 FILLING THE COOLING SYSTEM ................................................................................................................................ 81 
C.4 REMOVING AND REPLACING THE RADIATOR.......................................................................................................... 81 
C.5 DYNAMO AND FAN BELT ADJUSTMENT.................................................................................................................. 81 
C.6 COLD WEATHER PRECAUTIONS .............................................................................................................................. 83 
C7 REMOVING THE WATER PUMP, ............................................................................................................................... 83 
C.8 DISMANTLING AND REASSEMBLING THE WATER PUMP ........................................................................................ 83 
THE WATER PUMP AND THERMOSTAT COMPONENTS ................................................................................................ 85 
KEY TO THE WATER PUMP AND THERMOSTAT COMPONENTS .................................................................................... 86 
C.9 RADIATOR PRESSURE VALVE................................................................................................................................... 87 
THE COOLING SYSTEM COMPONENTS.......................................................................................................................... 89 
KEY TO THE COOLING SYSTEM COMPONENTS.............................................................................................................. 89 
SECTION D THE FUEL SYSTEM.................................................................................................................... 91 
KEYTO THE CARBURETTER COMPONENTS ................................................................................................................... 92 
D.1 REMOVING THE FUEL TANK.................................................................................................................................... 93 
D.2 REMOVING THE FUEL PUMP................................................................................................................................... 93 
D.3 CONSTRUCTION OF THE FUEL PUMP...................................................................................................................... 93 
D.4 ACTION OF THE FUEL PUMP ................................................................................................................................... 94 
D.5 DISMANTLING AND REASSEMBLING THE FUEL PUMP............................................................................................ 94 
D.6 RESETTING THE DIAPHRAGM FOR CONTACT BREAKER "THROW-OVER"................................................................ 97 

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D7. TRACING FUEL PUMP TROUBLES............................................................................................................................ 99 
D.8 FUEL PUMP MAINTENANCE ................................................................................................................................. 100 
D.9 CARBURETTERS .................................................................................................................................................... 100 
D.10 CARBURETTER ADJUSTMENTS............................................................................................................................ 101 
D.11 REMOVING AND REPLACING THE CARBURETTERS ............................................................................................. 104 
D.12 CENTERING THE JET............................................................................................................................................ 105 
D.13 SOURCES OF CARBURETTER TROUBLE ............................................................................................................... 105 
D.14 AIR CLEANERS..................................................................................................................................................... 107 
D.15 MODIFIED CARBURETTER DAMPER ASSEMBLIES ............................................................................................... 107 
SECTION E THE CLUTCH............................................................................................................................. 108 
GENERAL DESCRIPTION .............................................................................................................................................. 109 
E.1 ADJUSTMENT........................................................................................................................................................ 110 
E.2 MASTER CYLINDER ................................................................................................................................................ 111 
E.3 SLAVE CYLINDER ................................................................................................................................................... 112 
E.4 BLEEDING THE CLUTCH SYSTEM............................................................................................................................ 113 
E.5 REMOVING THE CLUTCH ....................................................................................................................................... 113 
E.6 DISMANTLING THE CLUTCH .................................................................................................................................. 114 
E.7 ASSEMBLING THE CLUTCH .................................................................................................................................... 115 
E.8 ADJUSTING THE RELEASE LEVERS.......................................................................................................................... 115 
E.9 REFITTING THE CLUTCH......................................................................................................................................... 116 
E.10 SERVICING THE CLUTCH ...................................................................................................................................... 116 
SERVICE TOOLS ........................................................................................................................................................... 120 
SECTION F THE GEARBOX..................................................................................................................... 121 
GENERAL DESCRIPTION .............................................................................................................................................. 124 
F.1 REMOVING THE GEARBOX .................................................................................................................................... 124 
F.2 DISMANTLING THE GEARBOX ............................................................................................................................... 124 
F.3 DISMANTLING THE THIRD MOTION SHAFT ........................................................................................................... 125 
F.4 ASSEMBLING THE THIRD MOTON SHAFT .............................................................................................................. 125 
F.5 LAYSHAFT GEAR .................................................................................................................................................... 125 
F.6 ASSEMBLING THE FIRST MOTION SHAFT............................................................................................................... 126 
F.7 ASSEMBLING THE REAR EXTENSION ..................................................................................................................... 126 
F.8 ASSEMBLING THE GEARBOX ................................................................................................................................. 126 
F.9 RENEWING THE GEARBOX EXTENSION OIL SEAL................................................................................................... 127 
F.10 REFITTING THE GEARBOX FRONT COVER ............................................................................................................ 127 
SERVICE TOOLS ........................................................................................................................................................... 128 
SECTION G THE PROPELLER SHAFT....................................................................................................... 131 
GENERAL DESCRIPTION .............................................................................................................................................. 131 
G.1 LUBRICATING THE UNIVERSAL JOINTS.................................................................................................................. 131 
G.2 TESTING FOR WEAR.............................................................................................................................................. 131 
G.3 REMOVING THE PROPELLER SHAFT...................................................................................................................... 132 
G.4 DISMANTLING THE PROPELLER SHAFT ................................................................................................................. 132 
G.5 TO EXAMINE AND CHECK FOR WEAR.................................................................................................................... 134 
G.6 REASSEMBLING THE SHAFT .................................................................................................................................. 134 
G.7 REPLACING THE PROPELLER SHAFT ...................................................................................................................... 134 
G.8 MODIFIED PROPELLER SHAFT............................................................................................................................... 135 
SECTION H THE REAR AXLE ...................................................................................................................... 136 
KEY TO THE REAR AXLE COMPONENTS ....................................................................................................................... 137 

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GENERAL DESCRIPTION .............................................................................................................................................. 138 
LUBRICATION.............................................................................................................................................................. 138 
H.1 REMOVING AND REPLACING AHUB EXTENSION AND AXLE SHAFT ...................................................................... 139 
H.2 REMOVING AND REPLACING AHUB ..................................................................................................................... 139 
H.3 RENEWING THE BEVEL PINION OIL SEAL............................................................................................................... 140 
H.4 REMOVING THE DIFFERENTIAL PINIONS .............................................................................................................. 140 
H.5 REPLACING THE DIFFERENTIAL PINIONS .............................................................................................................. 141 
H.6 DISMANTLING THE CROWN WHEEL AND PINION................................................................................................. 141 
H.7 ASSEMBLING AND SETTING THE CROWN WHEEL AND PINION ............................................................................ 142 
H.8 REMOVING AND REFITTING THE AXLE.................................................................................................................. 151 
SERVICE TOOLS ........................................................................................................................................................... 154 
SECTION J THE STEERING GEAR ............................................................................................................ 158 
KEY THE STEERING GEAR ............................................................................................................................................ 159 
GENERAL DESCRIPTION .............................................................................................................................................. 160 
MAINTENANCE ........................................................................................................................................................... 160 
J.1 REMOVING AND REPLACING THE STEERING WHEEL ............................................................................................. 160 
J.2 REMOVING THE STEERING COLUMN ..................................................................................................................... 161 
J.3 REMOVING THE STEERING COLUMN BUSHES........................................................................................................ 161 
J.4 REMOVING THE STEERING COLUMN UNIVERSAL JOINT........................................................................................ 161 
J.5 DISMANTLING THE UNIVERSAL JOINT ................................................................................................................... 161 
J.6 REMOVING AND REPLACING THE STEERING GEARBOX ......................................................................................... 162 
J.7 DISMANTLING THE STEERING GEARBOX ............................................................................................................... 162 
J.8 REASSEMBLING THE STEERING GEAR .................................................................................................................... 163 
J.9 STEERING COLUMN ALIGNMENT........................................................................................................................... 164 
J.10 CHECKING AND ADJUSTING FRONT WHEEL ALIGNMENT .................................................................................... 165 
J.11 FITTING AN ADJUSTABLE STEERING COLUMN ..................................................................................................... 166 
SERVICE TOOLS ........................................................................................................................................................... 166 
SECTION K THE FRONT SUSPENSION..................................................................................................... 167 
KEY TO THE FRONT SUSPENSION COMPONENTS........................................................................................................ 168 
GENERAL DESCRIPTION .............................................................................................................................................. 168 
K.1 REMOVING THE FRONT SUSPENSION ................................................................................................................... 169 
K.2 DISMANTLING THE SWIVEL PINS........................................................................................................................... 170 
K.3 EXAMINING PARTS FOR WEAR.............................................................................................................................. 170 
K.4 REASSEMBLING THE SWIVEL PINS ........................................................................................................................ 171 
K.5 REPLACING THE FRONT SUSPENSION ................................................................................................................... 172 
K.6 REMOVING AND DISMANTLING AFRONT HUB..................................................................................................... 173 
K.7 REASSEMBLING AND REPLACING AFRONT HUB................................................................................................... 173 
K.8 ADJUSTING THE FRONT HUB BEARINGS................................................................................................................ 173 
K.9 REMOVING AND REPLACING THE FRONT COIL SPRING......................................................................................... 174 
K.10 FITTING NEW RUBBER BUSHES ........................................................................................................................... 175 
K.11 ANTI-ROLL BAR ASSEMBLY.................................................................................................................................. 176 
K.12 FITTING THE ANTI-ROLL BAR............................................................................................................................... 176 
SERVICE TOOLS ........................................................................................................................................................... 177 
K.10 THE ANTI-ROLL BAR EQUIPMENT COMPONENTS ............................................................................................... 178 
SECTION L THE HYDRAULIC DAMPERS .................................................................................................. 179 
MAINTENANCE ........................................................................................................................................................... 179 
L.1 TOPPING UP .......................................................................................................................................................... 179 
L.2 REMOVING AND REPLACING REAR DAMPERS....................................................................................................... 179 

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L.3 REMOVING AFRONT DAMPER .............................................................................................................................. 180 
L.4 TESTING THE DAMPERS......................................................................................................................................... 180 
SECTION M THE BRAKING SYSTEM ......................................................................................................... 181 
GENERAL DESCRIPTION .............................................................................................................................................. 181 
BRAKE UNITS .............................................................................................................................................................. 181 
MASTER CYLINDER...................................................................................................................................................... 181 
MAINTENANCE ........................................................................................................................................................... 182 
M.1 ADJUSTING THE BRAKE PEDAL............................................................................................................................. 182 
M.2 PRIMING AND BLEEDING THE BRAKE SYSTEM (EXPELLING AIR) .............................................................................. 183 
M.3 REMOVING THE MASTER CYLINDER .................................................................................................................... 183 
M.4 DISMANTLING THE MASTER CYLINDER............................................................................................................... 184 
M.5 ASSEMBLING THE MASTER CYLINDER.................................................................................................................. 184 
M.6 REPLACING THE MASTER CYLINDER .................................................................................................................... 185 
M.7 REMOVING ABRAKE UNIT ................................................................................................................................... 185 
M.8 DISMANTLING ABRAKE UNIT .............................................................................................................................. 186 
M.9 ASSEMBLING ABRAKE UNIT ................................................................................................................................ 187 
M.10 REPLACING ABRAKE UNIT ................................................................................................................................. 188 
M.11 REMOVING THE FRICTION PADS........................................................................................................................ 188 
M.12 REPLACING THE FRICTION PADS........................................................................................................................ 188 
M.13 RELINING THE HAND BRAKE .............................................................................................................................. 189 
M.14 ADJUSTING THE HAND BRAKE ........................................................................................................................... 189 
M.15 REMOVING THE HAND BRAKE CABLE ................................................................................................................ 190 
M.16 REMOVING ABRAKE DISC.................................................................................................................................. 190 
M.17 REPLACING ABRAKE DISC.................................................................................................................................. 190 
M.18 FLEXIBLE HOSES................................................................................................................................................. 191 
SERVICE TOOL............................................................................................................................................................. 192 
SECTION N. ELECTRICAL EQUIPMENT.................................................................................................... 193 
GENERAL DESCRIPTION .............................................................................................................................................. 193 
N.1 BATTERY MAINTENANCE...................................................................................................................................... 193 
N.2 DYNAMO .............................................................................................................................................................. 195 
N.3 REMOVING AND REPLACING THE DYNAMO......................................................................................................... 196 
N.4 DISMANTLING THE DYNAMO ............................................................................................................................... 196 
N.5 SERVICING THE DYNAMO ..................................................................................................................................... 196 
N.6 THE STARTER ........................................................................................................................................................ 199 
N.7 REMOVING AND REPLACING THE STARTER.......................................................................................................... 199 
N.8 SERVICING THE STARTER ...................................................................................................................................... 199 
N.9 THE CONTROL BOX ............................................................................................................................................... 201 
N.10 FUSES ................................................................................................................................................................. 204 
N.11 THE ELECTRIC HORN ........................................................................................................................................... 204 
N.12 FLASHING DIRECTION INDICATORS .................................................................................................................... 204 
N.13 THE WINDSHIELD WIPER .................................................................................................................................... 205 
N.14 THE HEADLAMPS ................................................................................................................................................ 207 
N.15 THE LIGHT UNITS ................................................................................................................................................ 207 
N.16 REMOVING THE LIGHT UNITS ............................................................................................................................. 207 
N.17 SETTING THE HEADLAMPS.................................................................................................................................. 207 
N.18 REPLACING HEADLAMP BULBS........................................................................................................................... 208 
N.19 REPLACING THE LIGHT UNITS ............................................................................................................................. 209 
N.20 THE TAIL-LAMPS AND STOP-LIGHTS ................................................................................................................... 209 
N.21 CLEANING THE LAMPS........................................................................................................................................ 209 

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N.22 THE SIDELAMPS.................................................................................................................................................. 209 
N.23 THE NUMBER-PLATE ILLUMINATION ................................................................................................................. 209 
N.24 THE PANEL AND WARNING LIGHTS .................................................................................................................... 210 
WIRING DIAGRAM ...................................................................................................................................................... 211 
KEY TO WIRING COLOURS........................................................................................................................................... 213 
N.25 REPLACEMENT BULBS........................................................................................................................................ 213 
N.26 FITTING AFOG LAMP.......................................................................................................................................... 214 
N.27 LOCATION AND REMEDY OF FAULTS .................................................................................................................. 214 
CHARGING CIRCUIT .................................................................................................................................................... 215 
STARTER MOTOR ........................................................................................................................................................ 215 
LIGHTING CIRCUITS..................................................................................................................................................... 216 
WINDOWLESS YOKE DYNAMO ................................................................................................................................... 216 
N.29 MODIFIED CONTROL BOX................................................................................................................................... 216 
N.30 HEADLAMP BEAM SETTING................................................................................................................................ 217 
N.31 DRY-CHARGED BATTERIES.................................................................................................................................. 217 
N.32 MODIFIED EUROPEAN LIGHT UNIT..................................................................................................................... 218 
SECTION NN (MGA 1600)............................................................................................................................. 219 
KEY TO WIRING DIAGRAM (R.H.D., AND L.H.D.).......................................................................................................... 221 
CABLE COLOUR CODE ................................................................................................................................................. 221 
NN.1 FRONT PILOT AND FLASHING INDICATOR LAMPS .............................................................................................. 222 
NN.2 REAR FLASHING INDICATOR LAMPS................................................................................................................... 222 
NN.3 REPLACEMENT BULBS........................................................................................................................................ 222 
NN.4 HEADLAMPS ...................................................................................................................................................... 223 
NN.5 LUCAS C4011 DYNAMO...................................................................................................................................... 223 
NN.6 DISMANTLING AC40/1 DYNAMO ...................................................................................................................... 223 
NN.7 SERVICING AC40/1 DYNAMO ............................................................................................................................ 225 
NN.8 MODIFIED RB106/2 CONTROL BOX.................................................................................................................... 225 
NN.9 MK.II SEALED-BEAM HEADLAMPS ..................................................................................................................... 226 
SECTION O THE WHEELS, TYRES, AND JACKING................................................................................. 227 
GENERAL..................................................................................................................................................................... 227 
O.1 TYRE MAINTENANCE ............................................................................................................................................ 227 
O.2 JACKING UP THE CAR............................................................................................................................................ 228 
O.3 REMOVING AND REPLACING ROAD WHEELS........................................................................................................ 228 
O.4 VALVES ................................................................................................................................................................. 229 
O.5 TYRE REMOVAL .................................................................................................................................................... 229 
O.6 THE IMPORTANCE OF BALANCE ........................................................................................................................... 230 
O.7 FITTING TYRES AND TUBES ................................................................................................................................... 230 
SECTION P LUBRICATION........................................................................................................................... 234 
P.1 DAILY SERVICE....................................................................................................................................................... 235 
P.2 1,000 MILES (1600 KM.) SERVICE........................................................................................................................... 235 
P. 33,000 MILES (4800 KM.) SERVICE .......................................................................................................................... 237 
P.4 6,000 MILES (9600 KM.) SERVICE........................................................................................................................... 239 
P.5 12,000 MILES (19200 KM.) SERVICE....................................................................................................................... 243 
SECTION R THE CHASSIS........................................................................................................................... 245 
GENERAL DESCRIPTION .............................................................................................................................................. 245 
R.1 FRAME REPAIRS .................................................................................................................................................... 245 
R.2 INVESTIGATION OF DAMAGED CHASSIS ............................................................................................................... 246 