BSA M20 Parts & Spares
The M20 is the side-valve single BSA built in enormous numbers for the War Department, and then kept in production long enough that civilian machines outlasted the military ones in daily use. It is a simple engine to work on and a forgiving one to own, which is why so many are still running on parts that were never expected to last this long.
Obsolete Bike Parts holds over thirty M20 line items, most of them shared with the larger M21 and several with the overhead-valve M33: valves and guides, gasket sets, piston rings in standard and oversize, clutch friction plates, chaincases, exhaust pipes and silencers.
- € 44,00 Select options This product has multiple variants. The options may be chosen on the product page
- € 45,00 Select options This product has multiple variants. The options may be chosen on the product page
M20, M21 or M33?
BSA’s heavyweight singles were built around one set of cases. The M20 is the 500 side-valve, the M21 the 600 side-valve, and the M33 pairs that bottom end with an overhead-valve top end from the B33. Cycle parts, chaincases, clutches and gearbox components are largely common to all three, while anything that follows the bore, the valves or the head belongs to one of them alone. That is why our listings often name two or three models at once. War Department machines differ again in their electrics and ancillaries, and reproduction parts are not always made to the military pattern.
What we stock
- Valve gear: inlet and exhaust valves with matching guides, sold as sets
- Sealing: engine gasket sets and cylinder head gaskets
- Pistons: ring sets in standard and oversize
- Transmission: clutch friction plates, engine and gearbox sprockets, front chaincase
- Exhaust: chrome plated pipes and silencers
- Bottom end: big end assemblies
Check the numbers first
Send us the frame and engine numbers before you order. A machine that has been through military and then civilian service rarely still carries all of its original parts.