BSA Pre unit A7 A10 - Gearbox & Clutch

We are specialists in gearbox rebuilds on the BSA 'A’ series models including the STD, SC and close ratio RTT2, 

  • Full Gearbox rebuild
  • Mainshaft Regrinds
  • Layshaft regrinds
  • Special bushes made to size
  • Replacement gears
  • Clutch arm pivot repair
  • Alloy welding
  • Blasting & Polishing
  • SRM sprocket nut with oil seal
  • Replacement complete 4 spring clutch
  • Belt drive Primary with Alloy Clutch



The gearboxes are stripped, carefully checked and an estimate is produced for the work and parts required for the rebuild. All the individual costs are itemised. It is very common to find wear in the main and lay shaft bushes and shafts. Mainshaft and layshafts can be reground to restore the bearing surface and then new bushes made to size and fitted to the casings.bushes Worn gears are replaced along with the sleeve gear bushes and the kickstart ratchet gear bush on the mainshaft. The gearbox outer covers can be polished. All threads are checked prior to the final assembly,helicoils are used where the thread cannot be salvaged. New sprockets, tab washers and modern oil seals are used throughout the rebuild. we also fit new 5 speed clusters into the original gearbox shell.

The SRM sprocket nut with oil seal (shown above) helps prevent oil escaping from the sleeve gear when the bike is leaning over on the side stand.



We can supply quality parts to rebuild and renovate your clutch and primary chain. Careful assembly and adjustment make for a smooth clutch action. We can supply complete 4 spring clutch conversions to replace the troublesome 6 spring clutch ( swinging arm models only) or the ultimate upgrade is a complete alloy clutch and belt drive to replace the chain. Our conversion allows you to use the original engine spring shock absorber unit and also features a sealed bearing in the rear of the clutch basket so the system can be run dry – no more leaky primary chaincase.