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BSA WDM20 WORKSHOP MANUAL Private L. Wilkings, Essex Regiment, Somewhere in Holland INDEX GENERAL Pages Pages Brakes 28 Front Forks 23 Carburetter 10 Gearbox and Gearchange 25 Clutch 21 Hubs
BSA WDM20 WORKSHOP MANUAL Private L. Wilkings, Essex Regiment, Somewhere in Holland 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 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 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 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 1 USEFUL DATA Engine bore 82 mm Engine stroke M20 94 mm Engine stroke M 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/ Tyre Pressure 22psi Piston ring gap Piston clearance Bottom of skirt Piston Ring side clearance.002 -.004 Ignition timing 7/16 BTDC Magneto point gap.012 Spark plug gap 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 THE LUBRICATION SYSTEM 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. 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 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 LUBRICATION Fig 2. Lubrication Chart 4 LUBRICATION CHART No PART Lubricant Type of Daily 250 Miles General Lubrication (Inclusive) 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 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 THE ENGINE EXPLODED VIEW Fig. 3. Top half of engine (exploded view) 6 THE ENGINE EXPLODED VIEW Fig.4. Crankcase half of engine (exploded view) 7 ENGINE ADJUSTMENTS Which can be carried out without dismantling OIL PRESSURE VALVES As described under the heading How the Lubrication System Works on page 3 there are two ball valves incorporated in the lubrication system to prevent the transfer of oil from the tank to the crankcase. The spring loaded valve is located in the delivery passage between the pump and the big-end, and lies behind the hexagon plug at the lowest point of the timing cover (see Fig. 5). Adjustment is carried out by means of the cable adjuster at the side of the tappet chest. Fig. 6. Ball valve below return pump. Fig. 5. Pressure valve in timing cover. Should any foreign matter lodge between the ball and its seating oil will gradually transfer from the tank when the machine is left standing, and when the engine is started up there will be a heavy discharge of blue smoke from the exhaust. To rectify, remove the plug, spring and ball. The simplest way of removing the ball is to hold the hand close to the orifice and gently turn the engine over, when the ball will be forced out. Clean the ball and the seating, and if on replacing there is still doubt as to whether the ball is seating properly, insert a small punch against the ball and deal it a sharp tap with a light hammer. Finally replace the spring and plug. The other ball valve is located between the return pump (Fig. 6), and apparent failure of the return pump may be due to this ball having stuck in its seating. To rectify, remove the pump cover plate, insert a piece of wire into the valve orifice and lift the ball off its seating. Should the trouble keep recurring it may be necessary to fit a new base plate to the pump. On no account remove the oil pump unless it is absolutely necessary. EXHAUST VALVE LIFTER The peg on the exhaust valve lifter inside the tappet chest must always be well clear of the collar on the exhaust tappet (see Fig. 7), otherwise the engine will be noisy and the tappet clearances seriously affected. Failure to check that there is clearance at this point may result in a badly burnt exhaust valve. TAPPET ADJUSTMENT Before any attempt is made to adjust tappet clearances, check that the exhaust valve lifter is correctly adjusted as explained in the previous paragraph. To check and adjust tappet clearances, it is most essential, owing to the special design of the cam form (see Fig. 8), that the following procedure be adhered to. Fig. 7. Tappet and exhaust valve lifter. Rotate engine forward until the inlet valve has just closed (until tappet is just free to rotate). Now adjust the exhaust tappet clearance to.012. Turn engine forward again until the exhaust tappet clearance is just taken up (but before valve actually starts to lift). Now adjust inlet tappet clearance to.010 8 With the cover removed, take off the nut locking the magneto pinion on its shaft, and with the aid of a magneto pinion extractor (Fig. 10) release the pinion on its taper. (Note that the pinion is held on its shaft by a plain taper only, and can only be released with safety by using the proper extractor.) Fig. 8. Instructions for setting tappets The actual adjustment is carried out by releasing the locknut (B) (Fig. 8), holding the tappet with a spanner on the flat (C), and screwing the tappet head (A) either up or down. When correct clearance is obtained, the locknut must be tightened against the tappet head. It is advisable, after locking up, to check clearance again, to make sure that the adjustment has not been affected. Tappet adjustment should always be carried out with the engine dead cold, and the clearances recommended above regarded as a minimum, especially in the case of the exhaust valve. IGNITION TIMING It is a rare occurrence for the magneto pinion to slacken off and disturb the ignition setting, and it is not advisable to interfere with the setting unless it is known to be at fault. It is however advisable to check over the timing after carrying out any adjustment to the magneto contact points, as a slight variation of the points tends to advance or retard the timing. (Opening the points advances timing, closing them retards timing). If the timing requires re-setting, first remove the timing cover, and in so doing take care not to damage the small nozzle in the timing cover which feeds oil to the hollow crankshaft. Fig. 9. Ignition timing, Check that the fully open gap is correct to gauge (not exceeding.012 ). To re-set timing, turn engine forward until piston reaches top dead centre on the compression stroke (see Fig. 9). Now turn engine backwards until piston has descended 7/16. With ignition control at full advance turn contact breaker in its direction of rotation until the points are just about to open (not more than.002 open). Lightly tighten the magneto pinion nut and carefully check figures and positions. Then tighten nut properly and re-check. Fig. 10. Magneto pinion extractor. 9 CARBURETTER To maintain the efficiency of the carburetter it should be cleaned periodically by entirely dismantling it and washing each part in clean petrol. Renew any worn parts, particularly in the needle valve if the head has a distinct ridge at the point of seating, throttle valve if excessive side play is present or taper needle and clip, if it is possible to rotate the needle freely in the clip. When reassembling, make sure that the taper needle is refitted into the correct groove, is securely locked by the clip, and that it enters the central hole in the top of the jet block. Also verify that the needle valve enters the top of the float chamber easily, the mixing chamber flange joint is airtight, and the needle valve clip registers correctly in it s groove. It will, of course, be necessary to reset pilot adjusting screw. NEEDLE POSITION. Needle positions are counted from the top of the needle and the groove nearest the top is No. 1. THROTTLE STOP. The position of the throttle valve is set by means of the throttle stop screw (See Fig 4), the throttle control being closed during this adjustment. Alternatively, if the screw is adjusted clear of the throttle valve, the engine will be shut off in the normal way by the control. combination of throttle positions and air adjustment, the desired idling is secured. MIXTURE STRENGTHS. Weak mixture is indicated by difficult starting, a tendency for the engine to spit back through the carburetter (indicated by blue fumes from the air intake). The engine knocks, and runs hot with loss of power. The spark plug electrode shows indications of intense heat, and the mica insulation becomes white. If spitting back occurs, raise the needle in the throttle valve. Test by lowering the air valve gently. Engine revs will rise when the air valve is lowered slightly below the throttle valve. Rich mixture indications are heavy thumpy running with emission of black smoke from the exhaust pipe. As the throttle is opened heavy blowback of fuel is observed from the carburetter air intake. If the engine speed does not increase progressively as the throttle is raised, lower the needle in the throttle valve. The normal needle setting is with the clip in No. 2 groove. SPARKING PLUG The machine is supplied with a K.L.G. type F70 sparking plug, and is of a three-piece construction. After dismantling, the lower (taper) portion should be scraped clean of all carbon deposit. Note: Earlier models are fitted with type L777 plug a three-point plug with mica insulation. Where mica insulation is used, the mica must on no account be scraped, but cleaned with petrol and a rag. The inside of the body should be well scraped, and the earth point cleaned. Fig. 11. Carburetter adjustments. PILOT ADJUSTMENT. To weaken the slow running mixture, screw the pilot air adjuster outwards and to enrich the slow running mixture, screw the adjuster inwards. Screw the air adjuster home in a clockwise direction. Warm up the engine, close the air lever and set the throttle about 1/8 th open. Gently close the throttle when the mixture will prove too rich unless air leaks are present. Gradually unscrew the pilot air adjuster, when the engine speed will increase and must be again reduced by gently closing the throttle, until by a When re-assembling, verify that the internal washer is in place before inserting the electrode. Having tightened the gland nut, set the earth point to give a gap of to This may mean bending the earth point towards the centre electrode, or if the gap is too narrow, prising it outwards. The centre electrode must not be levered towards the earth point. The external washer should be replaced if it is broken or has been completely flattened. SYMPTOMS OF MINOR PLUG TROUBLES. Misfiring especially at high speeds and under heavy pulling at lower speeds, invariably indicates that the gap setting of the plus is too wide, whilst erratic slow running can be accounted for by too narrow a gap setting. An over rich mixture will result in trouble in the form of an excess deposit of soot on the internal insulation of the plus with consequent shorting inside the plug. A faulty high tension cable, or the magneto contact points being out of adjustment will also account for the plug misfiring. 10 ENGINE DISMANTLING for DECARBONISING When decarbonising, it is not necessary or desirable to dismantle the cylinder barrel, unless it is suspected that the valves, pistons or its rings are the cause of some trouble. It is sufficient to remove the cylinder head and gasket thus exposing the piston and valves. REMOVING CYLINDER HEAD To detach cylinder head, disconnect sparking plug lead, remove steady strap and the 10 cylinder head bolts. Head can then be lifted off. Rotate the engine until the piston is at the top of its stroke and scrape it with an old penknife, taking great care not to damage the piston crown. Then clean the cylinder head and replace, tightening the bolts in the order shown in Fig. 24. If the valve seats are suspected of gas leakage, due to insufficient tappet clearances or other causes these should be remedied. It is possible to grind in the valves in position, but it is preferable to remove the barrel from the crankcase so that the work may be carried out on the bench, and at the same time the piston and rings inspected. When removing the cylinder barrel, the simplest way is to lift it up and tilt it forwards into the front angle of the frame. The piston should be steadied as it emerges from the barrel to prevent possible damage. Cover the crankcase mouth with rag to prevent dust and grit falling in. REMOVING CYLINDER BARREL To remove cylinder barrel, first turn off petrol taps and detach carburetter. This can be tied to frame out of the way. Next, the exhaust pipe and silencer should be removed complete. The exhaust valve lifter should be unscrewed from the tappet chest until the eccentric peg on the lifter is clear of the tappet head. Uncouple the exhaust valve lifter by removing Fig. 13. Inserting valve guides REMOVING THE VALVES To remove the valves an extractor as shown in Fig. 12 may be used. If the proper extractor is not available, the valves may be removed by laying the cylinder barrel on a bench (valve heads downwards) and compressing the valve springs with the aid of a piece of tube (suitably slotted), while an assistant removes the cotters. Clean all carbon from the ports and check valve guides for wear. FITTING NEW VALVE GUIDES If new guides are to be fitted, the old ones may be extracted (from below) by means of a simple punch (consisting of a bar of steel of not more than 5/8 diameter Fig. 13). The new guides can be driven in from the top with the same punch and it is important that the dimensions from the top of the guide to the cylinder head joint (as shown in Fig. 14) should be carefully observed. After the new guides have been inserted, the valve seats should be re-cut with a pilot cutter to ensure concentricity of seats and stems (see Fig. 14). Note that the exhaust valve guide only has it s upper end counterbored. Fig. 12. B.S.A. Valve removing tool. the pin at the lever end. Now remove the five cylinder base nuts (four outside and one inside tappet chest), and cylinder barrel can be lifted off. GRINDING IN V
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