BSA M20 500CC Workshop Repair Manual All Models Covered

Book No. 100/BC2C Air Publication No. 1657B, Vol.1. Parat2 Maintenance Manual And Instruction Book For MOTOR CYCLE (SOLO) 500 c.c. s.v. Model M20 Downloaded from www.Manualslib.com manuals search engine

INDEX – GENERAL Pages Pages Brakes 28 Front Forks 23 Carburetter 10 Gearbox and Gearchange 25 Clutch 21 Hubs 27 Charging System 36 Ignition System 32 Electrical Wiring System 30-31 Lighting and Accessories 42 Engine Adjustments 8 Lubrication System 3 Engine – Complete dismantling 12 Lubrication Chart 4-5 Engine – Decarbonising 11 Steering Head 28 Engine – re-assembly 16 Transmission 20 Engine – removal from frame 12 Useful Data 2 INDEX – DETAILS Pages Pages BRAKES Ignition System - continued Adjustment – Relining 28 Slipping clutch – sparking plug - CARBURETTER Suppressor - immobiliser 33 Mixture – Needle position – Pilot adjustment – Re-assembling and testing slipping clutch 35 Throttle stop. 10 Lighting and Accessories ENGINE ADJUSTMENTS Headlamp – Tail lamp – Cables - Lighting Oil-pressure valves – Exhaust valve lifter 8 switch 42 Tappets – Ignition timing 8-9 Horn 43 ENGINE DISMANTLING Wiring diagrams 30-31 Cylinder head – Cylinder barrel – Valves 6-7 Valve grinding – Valve guides, removal FRONT FORKS and replacement 11 Adjustment 28 Piston and Rings – Checking ring gap – Dismantling – fitting new spring – re-assembly 29 removing engine from frame 12 Removing Magdyno pinion 13 GEARBOX Oil pump, removal and dismantling – Removal – dismantling 23 “Splitting” crankcase – removing Dismantling Gearchange – Re-assembling Bearings 14 Gearbox 24 Removing cam spindles – dismantling Re-assembling gearchange 25 flywheels – reboring cylinder - fitting Replacing gearbox 26 new cylinder lining. 15 ENGINE RE-ASSEMBLY HUBS Flywheel assembly and alignment 16 Rear – adjustment – dismantling and Replacing oil pump – tappets – replacing Re-assembly 27 bearings – re-assembling crankcase - Front 27-28 Replacing timing gears & magdyno 17 Replacing piston – cylinder barrel - timing LUBRICATION Cover – cylinder head – exhaust valve Engine lubricating system 3 lifter – refitting engine in frame. 18 Lubrication chart 4 ELECTRICAL EQUIPMENT Hubs – Brake cam spindles - Speedometer Charging System Drive – Filters – Rear chain – Dynamo - Dynamo Gearbox 5 Testing – Removal and Replacement 36 Oil pump – removal – dismantling and Dismantling – Brushes - Commutator 37 Re-assembly 14 Field coil, testing and removing - Armature – Bearings 38 TRANSMISSION Re-assembly 39 Clutch – adjustment 20 Cut-out and Regulator 39 Clutch – dismantling 21 Cleaning contacts – setting regulator - Clutch – re-assembly 22 Cut-out 40 Chaincase - removal 12 Ammeter – Removal and Replacement 41 Chaincase - replacement 18 Battery – Care of 41 Chain adjustment 20 Ignition System Wheel alignment 21 Magneto lubrication – adjustment – testing - Cleaning contact breaker – H.T. cable - SHOCK ABSORBER – Adjustment 28 Pick-up 32 Removal – dismantling – removing and STEERING HEAD testing armature 34 Adjustment 28 Re-assembly 35 Dismantling – re-assembly 29 Downloaded from www.Manualslib.com manuals search engine

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USEFUL DATA Engine bore 82 mm Engine stroke M20 94 mm Engine stroke M21 112 mm Engine Capacity 496cc Petrol tank capacity 3 gallons Oil tank capacity 5 pints Gearbox capacity 1 pint Inlet tappet clearance (cold) .010” Exhaust tappet (cold) .012” Compression M20 4,9:1 Compression M21 5:1 Tyres 3.25/3.50-19 Tyre Pressure 22psi Piston ring gap .008 - .012” Piston clearance Bottom of skirt .0035 - .0055” Piston Ring side clearance .002" - .004" Ignition timing 7/16” BTDC Magneto point gap .012” Spark plug gap .012 - .018” Carburetter- Jet 170 Carburetter- Needle 2nd notch Engine Sprocket 19 teeth Clutch sprocket 43 teeth Gearbox Sprocket 18 teeth Rear Wheel Sprocket 42 teeth Primary Chain 95 links Gear Ratio- Top 5.3 Gear Ratio- 3rd 7.0 Gear Ratio- 2nd 10.9 Gear Ratio- 1st 15.8 Downloaded from www.Manualslib.com manuals search engine

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THE LUBRICATION SYSTEM Fig. 1. Lubrication System The engine lubrication system is of the dry sump type operated by a double gear pump, situated in the bottom of the crankcase on the right-hand side. All oilways are internal except for the supply and return pipes from the tank. The oil flows from the tank to the supply pump (the top pair of gears) and thence past the pressure valve (A) to the two oilways feeding the cam spindles, and along the hollow mainshaft to the big end bearing. After lubricating the big end and circulating through the engine in the form of a mist, the oil drains down through a filter in the bottom of the crankcase, from which it is drawn by the return pump (lower pair of gears) past ball valve (C), and delivered up the return pipe to the tank, where it passes through a fine mesh filter into the tank itself. Incorrect seating of the ball valve (A), will allow oil to transfer from the tank to the engine, whilst the machine is stationary. If the ball valve (C) should get stuck in its seating, there will be no return of oil to the tank. To check the oil circulation open the tank filler cap and remove filter cap whilst the engine is running. Oil should be seen issuing from the return pipe from the crankcase. The tank and crankcase should be drained every 2,000 miles and replenished with clean oil. Any restriction in the pressure release pipe in the tank will cause an increase in pressure inside the oil tank, and will result in leakage of oil at the filler cap. This can be put right by inserting a length of flexible wire into the pipe at its lower end (just in front of the rear mudguard) and pushing the wire right up the pipe, thus clearing any obstruction. To remove the oil tank filter for cleaning, release the tank filler cap, release the filter tap thus exposed, and lift filter out. The filter should be placed in a can large enough to cover it with petrol, and thoroughly washed. Before replacing make sure that it is quite dry of petrol. The pump filter can be withdrawn after removing the cover plate (B) and should be thoroughly washed with petrol, dried and replaced. NOTE. It is not advisable to remove the oil pump unless the pump is definitely faulty. 3 Downloaded from www.Manualslib.com manuals search engine

LUBRICATION Fig 2. – Lubrication Chart Downloaded from www.Manualslib.com manuals search engine

4 LUBRICATION CHART No PART Lubricant Type of Lubrication Daily 250 Miles (Inclusive) General FRAME GROUP 3 Front fork (top) CG-1 (AL) 1 nipple Grease Gun 2 Front fork (centre) CG-1 (AL) 1 nipple Grease Gun 4 Steering Stem (top) CG-1 (AL) 1 nipple Grease Gun 5 Steering Stem (bottom) CG-1 (AL) 2 nipple Grease Gun 7 Steering Head (top) CG-1 (AL) 1 nipple Grease Gun 6 Steering Head (bottom) CG-1 (AL) 1 nipple Grease Gun 8 Saddle nose pivot CG-1 (AL) 1 nipple Grease Gun 11 Front wheel hub CG-1 (AL) Re pack - Re pack w shops every 5000 miles 12 Rear wheel hub CG-1 (AL) Re pack - Re pack w shops every 5000 miles BRAKE GROUP 9 Brake pedal CG-1 (AL) 1 nipple Grease Gun 16 Brake cam (front) CG-1 (AL) 1 nipple Grease Gun 15 Brake cam (rear) CG-1 (AL) 1 nipple Grease Gun Bowden control wire OE-30 Oil Can Few Drops Foot brake linkage OE-30 Oil Can Few Drops ENGINE GROUP 1 Engine oil tank OE50 5 pints Replenish Replenish Drain & refill at 1000 miles (AO17) 19 Primary chain case OE50 Reservoir Replenish Replenish Drain & refill at 1000 miles (AO17) 1/20 Oil Filters OE50 Wash in petrol every 2000 miles IGNITION GROUP Advance Retard Cable etc OE30 Oil Can Few drops Contact breaker tappet OE30 Oil Can One drop 22 Contact breaker cam CG-1 (AL) Hand smear Slight smear Generator (drive end) WB-2 Re pack Re pack w shops 21 Generator (commutator end) OE30 Oil Can Few drops FUEL GROUP Air cleaner N/A Carburetter control cables OE30 Oil Can Few drops Throttle handle bar grip OE30 Oil Can Few drops TRANSMISSION GROUP 10 Speedometer drive CG-1 (AL) 1 nipple Grease Gun Speedometer cable OE30 Oil can Few drops 14 Gear box GO-90 1 pint Replenish Drain & refill each 6000 miles No 18 12 Clutch push rod OE-50 Oil can Few drops Clutch bowden control wire OE30 Oil can Few drops Clutch handle bar grip OE30 Oil can Few drops Rear chain OE30 Oil can Few drops Wash in paraffin and soak in oil OE- 50 every 2000 miles. Workshops 5 Downloaded from www.Manualslib.com manuals search engine

THE ENGINE – EXPLODED VIEW Fig. 3. Top half of engine (exploded view) 6 Downloaded from www.Manualslib.com manuals search engine

THE ENGINE – EXPLODED VIEW Fig.4. Crankcase half of engine (exploded view) 7 Downloaded from www.Manualslib.com manuals search engine

BSA M20 500CC Workshop Repair Manual All Models Covered

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