Related Manuals for BSA M20
Summary of Contents for BSA M20
- Page 1 Book No. 100/BC2C Air Publication No. 1657B, Vol.1. Parat2 Maintenance Manual Instruction Book MOTOR CYCLE (SOLO) 500 c.c. s.v. Model M20...
- Page 2 INDEX – GENERAL Pages Pages Brakes Front Forks Carburetter Gearbox and Gearchange Clutch Hubs Charging System Ignition System Electrical Wiring System 30-31 Lighting and Accessories Engine Adjustments Lubrication System Engine – Complete dismantling Lubrication Chart Engine – Decarbonising Steering Head Engine –...
- Page 4 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”...
- Page 6 THE LUBRICATION SYSTEM 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.
- Page 7 LUBRICATION Fig 2. – Lubrication Chart...
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Page 8: Lubrication Chart
LUBRICATION CHART PART Lubricant Type of Daily 250 Miles General Lubrication (Inclusive) FRAME GROUP Front fork (top) CG-1 (AL) 1 nipple Grease Gun Front fork (centre) CG-1 (AL) 1 nipple Grease Gun Steering Stem (top) CG-1 (AL) 1 nipple Grease Gun Steering Stem (bottom) CG-1 (AL) 2 nipple... - Page 9 THE ENGINE – EXPLODED VIEW Fig. 3. Top half of engine (exploded view)
- Page 10 THE ENGINE – EXPLODED VIEW Fig.4. Crankcase half of engine (exploded view)
- Page 11 ENGINE ADJUSTMENTS Which can be carried out without dismantling OIL PRESSURE VALVES Adjustment is carried out by means of the cable As described under the heading “How the Lubrication adjuster at the side of the tappet chest. 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.
- Page 12 damage the small nozzle in the timing cover which feeds oil to the hollow crankshaft. 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.
- Page 13 CARBURETTOR again reduced by gently closing the throttle, until by a To maintain the efficiency of the carburettor it should combination of throttle positions and air adjustment, be cleaned periodically by entirely dismantling it and the desired idling is secured. washing each part in clean petrol.
- Page 14 ENGINE DISMANTLING for DECARBONISING When decarbonising, it is not necessary or desirable When removing the cylinder barrel, the simplest way to dismantle the cylinder barrel, unless it is suspected is to lift it up and tilt it forwards into the front angle of that the valves, pistons or its rings are the cause of the frame.
- Page 15 will wear away the seat in the cylinder barrel and smooth surface all the way round. If the machine has cause the valve to become pocketed. Take great covered a considerable mileage, the valve springs may need replacing. Refit the valves, springs and cotters with the aid of the tool shown in Fig.
- Page 16 unscrew the latter. Then withdraw the spring and shown in Fig. 15 on which the engine can be cam sleeve, leaving the sprocket and chain in mounted. Alternatively, a lug on the crankcase may position. Next, take off the clutch. REMOVING CLUTCH.
- Page 17 The engine shaft nut should be removed and the means of a spring ring which must be removed plate holding the timing gears in position is detached before extracting the race. by removal of the six fixing bolts, three of which screw into the crankcase casting and have coarse threads, while the remaining three screw into the pinion spindles and have fine threads.
- Page 18 Bearing to give even extraction (Fig. 18). These operations will be considerably helped if the crankcase is first warmed, the most suitable method being by dipping in boiling water. If it is desired to remove the cam pinion spindles, they can easily be taken out by means of an extractor (Fig.
- Page 19 RE-ASSEMBLING THE ENGINE The need for extreme cleanliness cannot be over-emphasised. Parts should be thoroughly cleaned and all trace of any antirust preparations with which new parts may be coated must be removed. All bearing surfaces should be liberally smeared with engine oil when assembling. FLYWHEELS If the big end assembly is to be renewed it is as well to check the weight of the new components against...
- Page 20 CRANKCASE that the connecting rod is not visibly out of centre, Withdraw the bearings from the shaft and press them there is no necessity for any adjustment to be made. into their appropriate positions in the crankcase If the connecting rod is out of centre, it will be halves.
- Page 21 not be driven on very firmly but just tightly enough to compressed quite easily by hand while the barrel is prevent slip. Check the backlash between this pinion being replaced. and the idler. If excessive, the gears will be noisy; if Tighten the barrel down, not forgetting one nut is insufficient, a whining noise will result.
- Page 22 the spring (this does not apply after decarbonising). refilled with engine oil to the level plug, before the Lock the central nut up tight, when the clutch and machine is used. primary chain are in position. If there is any suspicion that the rubber pipes from Fit the clutch on the gearbox mainshaft (this does not the oil tank to the crankcase are faulty they should be apply after decarbonising) –...
- Page 23 TRANSMISSION Adjustments which can be carried out without dismantling CLUTCH ADJUSTMENT Two adjustments are provided at the clutch control arm on the gearbox outer cover. The adjustment, which is for the clutch push rod will be exposed when the rubber cover at the base of the arm is moved aside and consists of a grub screw and locknut.
- Page 24 necessary that the wheel alignment be checked with a straight edge and the see which gauge – 1, 2 or 3 – is the correct fit). If the machine is in the workshops, however, it is much better to use a wooden straight edge, in the normal manner, i.e., it should touch each wheel in two places.
- Page 25 RE-ASSEMBLY OF THE CLUTCH No adjustment is provided for altering he tension of The clutch is of straight-forward construction and a the ring and the ring must be screwed up tight. After study of Fig. 32 will show how the parts are carefully centralising sliding plate (in ear half of chaincase) with gearbox mainshaft, refit clutch assembly to mainshaft after cork...
- Page 26 REMOVING, DISMANTLING AND RE-ASSEMBLY OF THE GEARBOX AND GEAR CHANGE REMOVAL DISMANTLING THE GEARBOX Instructions as to the procedure to be adopted for It will greatly help work on the gearbox I it is held in a removal of the chaincase and clutch are contained in simple fixture such as that illustrated in Fig.
- Page 27 Next, remove the pin from the link rod between the Do not disturb the ballrace unless it is suspected of selector quadrant and the gearchange mechanism at being faulty. Wash it thoroughly in paraffin, to the latter end and unscrew the nut off the end of the remove all traces of oil, when any play will be gearchange spindle.
- Page 28 It is only possible to refit the shafts and their pinions order: Ratchet, bush, ratchet pinion, spring and in the box provided that the shafts are first shouldered nut. The latter should be tightened by assembled (with pinions in top gear position) outside finger pressure only.
- Page 30 Before the re-assembly is The replacement of the gearbox carried out a stage further, should not present any difficulties. loosely replace the When the box is in position and gearchange pedal and the fixing bolts are about to be check the operation of all tightened up, make sure that the flats just below the bolt heads gears by inspection through...
- Page 31 ADJUSTMENT, DISMANTLING AND RE-ASSEMBLY OF HUBS AND BRAKES REAR HUB (Fig. 39) on bench (shoes uppermost) and lever shoes upwards. They can then be drawn over and free of The rear wheel is of the quickly detachable type and cam and fulcrum pin. To replace, attach springs and the taper roller bearings are contained in the wheel reverse method of removal.
- Page 33 Re-positioned. Insert the wheel spindle, but before by gripping the shoe in a vice, inserting a chisel finally tightening the spindle nuts, the chain should be under one end and shearing the rivets off in finally adjusted and the wheel aligned by means of sequence.
- Page 34 REMOVAL AND DISMANTLING OF FRONT FORKS AND STEERING HEAD There is no necessity to disturb the electrical system opposite end of the head lug, and the extractor and as a whole, when removing the forks. The ballrace driven out together. instrument panel on the back of the headlamp is If the balance cups and cones are pitted, to even a retained by three screws, and if these are removed,...
- Page 35 CHAIN ALTERATIONS AND REPAIRS A chain rarely breaks if it is kept properly lubricated connecting link (C). The connection is made with an and adjusted. Usually it is worn out long before it additional spring link (D). If one end of the chain has reaches breaking point.
- Page 36 the chain has located on the sprocket teeth, engage pre-determined length; the measurement so obtained a gear and gently turn gearbox over with the can then be compared with the nominal length, the kickstarter. This will feed chain round gearbox difference being, the amount of wear that has taken sprocket.
- Page 37 THE ELECTRICAL EQUIPMENT THE WIRING SYSTEM Fig 46A. Simple wiring diagram for models fitted with ammeter. Fig 46B. Simple wiring diagram for models fitted without ammeter.
- Page 38 Fig. 46C. Wiring diagram in models fitted with ammeter. The Wiring System In the event of the wiring system requiring replacement, no difficulty should be experienced provided that the diagrams (Figs 46A, B, C and D) are carefully followed. It should be noted that Figs 46A and C apply only to machines on which an ammeter is fitted.
- Page 39 IGNITION (Section A) A(1) “MAGDYNO” TYPE M01 may be an internal fault in the magneto. The A(2) Magneto Routine Maintenance following procedure should, therefore, be adopted. Lubrication A (4) Magneto Contact Breaker – Cleaning The cam is lubricated by a wick, contained in the Remove the contact breaker cover and examine the contact breaker case, which must be given a few contacts.
- Page 40 A (7) Resistor and Immobiliser A (9) Magneto Slipping Clutch (see Fig. 49). Check for cracks in the insulation and for positive Description contacts of the high tension cable; always disconnect A shock absorbing drive is incorporated in the larger lead at sparking plug before unscrewing of the two gears, which take the drive from the immobilisers.
- Page 41 A (10) Removal from engine the screws (U, Fig. 51), earthing terminal (V), and Before the magdyno can be removed from the pillar (W) from the contact breaker end plate (X) and engine, it is first necessary to take off the timing remove the plate from the magdyno, together with cover.
- Page 42 A (14) Re-assembling. the housing. (Note that the cam is fitted with its flat Wash the bearings in petrol, dry thoroughly and side towards the armature). repack with high melting point grease. Fit ball races Fit the contact breaker body (A, Fig. 56) in position on armature shaft by means of a hand press and use on the location at the end of the shaft after making sure that the tappet (B) is free and is located...
- Page 43 After setting, by slackening or tightening the securing correctly located between the cover and the end of nut (F, Fig 49) prevent further movement by bending the magdyno. up the tab of the lock washer (E). Refit the dynamo Replace the pick-up, first checking that the brush and pack the gears with high melting point grease.
- Page 44 Fig. 59. Exploded view of dynamo B (3) Dynamo – Dismantling formed so that bedding to the commutator is (a) Bend back the tag on the washer (B, Fig. 59) unnecessary. locking the screw (C) securing the driving gear (D) and remove the screw.
- Page 45 Undercut the mica insulation between the segments Dynamo - Armature to a depth of 1/32” (fig. 61) with a hacksaw blade The testing of the armature winding requires the use ground down until it is only slightly thicker than the of a volt-drop test or a growler.
- Page 46 bush should be pressed in until it is flush with the face of the end bracket. Fit the felt ring in B (10) Cut-out and Regulator Unit, Type MCR1 the space between the bearing and the wall This unit houses the dynamo voltage regulator unit of the bearing housing.
- Page 47 (c) Start the engine and slowly increase the speed moveable armature (D). (Not under the stop rivet). until the voltmeter needle “flicks” and then steadies; Press the armature back against the armature frame this should occur at a voltmeter reading between the and down on to the top of the bobbin core with the limits given for the particular temperature of the feelers in position and lock the armature in position...
- Page 48 (c) To check the voltage at which the cut-out gravity as that in the cells. This should be measured operates, with the engine still running, the voltmeter by means of a hydrometer. should be connected between the “D” terminal and earth.
- Page 49 LIGHTING AND ACCESSORIES (Section C) C (1) Headlamp, Type DU42 focussing with the mask removed, until the smallest The main bulb should be 6 volt 24 watt. S.B.C. circle of light is obtained. Adjust by slackening the double contact type. The pilot bulb should be 6 volt screw in the clamping band and sliding the bulb 24 watt.
- Page 50 panel can be removed when the three fixing screws notches before retesting. If the adjustment screw is are withdrawn. The ends of all the cables are turned too far in a clockwise direction, a point will identified by means of coloured sleevings. The occur at which the armature pulls in but does not colour scheme and the diagram of connections are separate the contacts.
- Page 51 Change-over Switch Take out the three screws securing the panel plate A single lead connects the main lighting switch to the fitted at the back of the lamp and withdraw the panel change-over switch and two cables connect the (Fig. 76). Slacken the three screws in the switch change-over switch to the main and pilot bulb terminals and lift out the cables.
- Page 52 TOOL KIT SUPPLIED WITH THE MACHINE B.S.A. Description Part No. 33-9030 Tool Bag 29-9251 Magneto Spanner 66-9039 Sparking Plug Spanner 15-832 Box Spanner 29-9254 Hub Bearing Adjusting Spanner EB259 B.S.A. Double Ended Spanner 66-9036 Cylinder Base Nut Spanner 29-9253 Spanner Tommy Bar 66-9068 Detachable Wheel Spanner 28-4265...