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BSA Motorcycles

BSA M20 Specifications

Engine bore. . . . . . . . . . . . . . .82mm

Engine Stroke. . . . . . . . . . . . . 94mm

Engine Capacity (c.c.). . . . . . .496c.c

Petrol Tank capacity. . . . . . . . 3 gallons

Oil Tank capacity. . . . . . . . . . 5 pints

Gearbox capacity... 1 pint (approx.)

Tappet clearance (cold)-

Inlet. . . . . . . ..010"

Exhaust. . . . . .012"

Compression ratio. . . . . . . . . . .4.91

Tyres. . . . . . . . . . . . .. . . . 3.25-19"

Engine Sprocket. . . . . . . . . . . . 19 teeth

Clutch spocket. . . . . . . . . . . . . 43 teeth

Gearbox Spocket. . . . . . . . . . 18 teeth

Rear Wheel Spocket. . . . . . . . 42 teeth

Piston Ring gap. . . . . . . . . . . . 008"/.012"

Piston Ring side clearance. . . . .002"/.004"

Piston clearance-

Bottom of skirt. . . . . . . . . . . . . .0035"/.0055"

Gear Ratios-

Top. . . . . . . . . . . . . . . . . . . . . . 5.3

3rd. . . . . . . . . . . . . . . . . . . . . . . 7.0

2nd. . . . . . . . . . . . . . . . . . . . . . 10.9

1st. . . . . . . . . . . . . . . . . . . . . . . 15.8

Ignition setting (inches before

T.D.C fully advanced) . . . . . . . . . .7/16"

Contact breaker gap. . . . . . . . . . . .010"-.012"

Spark Plug (K.L.G .F70) gap. . . . . 018"-.020

Carburetter-

Jet. . . . . . . . . . . . . . . . . . . . . . . . . .170

Needle.. . . . . . . . . . . . . . . . . . . . . . 2nd notch

Primary Chain. . . . . . . . . . . . . . . . . .95 links

Sources: http://web.archive.org/web/20010309091125/http://www.btinternet.com/~m20/m20.html

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