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The gearbox cluster is pretty straightforward and almost impossible to assemble incorrectly.

Later first gears have a brass bush; earlier ones are plain.

Later fourth gears have undercut dogs; earlier ones have holes.

There are four different types of mainshaft. Make sure you have the correct one for your bike, otherwise the clutch won't fit.

Mainshaft 041701 was fitted to 350cc boxes number from 0 to 3757. 041703 was an improved main shaft fitted from box number 3758 onwards. The parts list shows this shaft was also fitted to the 250cc CSR. You need this shaft if your bike has a duplex primary chain.

Mainshaft 041263 was fitted to 250cc boxes number 0 to 9974 and 10064 to 10128 as a temporary measure. 043058 was fitted to box numbers 9975 to 10063 inclusive and all boxes after 10128 according to the manual (but there is no mention of this part in the spares list). You need this shaft if your bike has a simplex primary chain.

Early mainshafts 041701 and 041263 need clutch centre 043186. Later mainshafts 043058 and 041703 need clutch centre 043509.

Gears ratios are the same for all models (2.92, 1.85, 1.31, 1:1) except the CS, which has a higher ratio first gear (2.42:1) and the close-ratio box fitted to 1965-on CSRs (2.76, 1.75, 1.24, 1:1)

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