The engine and gearbox are held together as a unit by the rear engine plates and any extensive overhaul of the engine that involves separating the crankcase will necessitate removing the engine and gearbox units together. The primary chain cover, etc., should also be left in place. It is possible, however, to renew any of the gears or shafts in the gearbox without removing the housing from the frame, and only the replacement of the sleeve gear bearing, or lay-shaft ball-bearing that are both fitted to the housing would require its removal. The engine would then have to come out as well. The cylinder head steady, carburetter, and exhaust pipe must, of course, be removed. The air cleaner assembly and oil tank are attached to the frame at the top and to the rear engine plates at the bottom, and have to be removed as a preliminary to reach the rear engine plates.

The oil tank need not necessarily be drained before removal. Remove the dynamo; see Removal of Dynamo and Belt Cover. Take off the front section of the rear chain guard, it is attached to the primary chain cover by two ¼-in. B.S.F. nuts.

Disconnect the clutch and exhaust lift cable assemblies at the handlebar levers and pull the cables clear from any clips on the frame. Pull out the split cotter from the shock absorber collar. If the gearbox is to be dismantled it is a help if at this stage the gearbox end cover plate is removed from the gearbox end cover, and the gearbox mainshaft nut inside the opening loosened. The shaft can then be held from turning by applying the rear brake. Also loosen the shock absorber collar. Next remove the gearbox sprocket nut and pull the final drive sprocket off the shaft with the chain. The chain need not be removed unless it is to be cleaned or replaced. Take the weight of the unit on a block below the crankcase, and remove all bolts from the front engine plates and three from the rear plates. One at the top rear corner, one from the bottom rear corner, and one bolt passing through the frame lug, bottom front ends of the engine plates, and crankcase. On this last there is a distance piece between the frame lug and the engine plate on the right hand side. The whole unit can now be levered forwards and lifted out of the frame. 

Separation of Gearbox from Engine.

Remove the primary chain cover front half, the clutch, engine sprocket, and primary chain. and the rear half of the chain cover from the gearbox (see Primary Chain Cover). The bolt holding the engine plates to the crankcase is now accessible for removal after which the plates will pull away from the crankcase / gearbox assembly and rear engine