Taking a grinder to Britain's motorcycling heritage.
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Tuesday, 3 May 2011

Here In Lies The Rub.......................

The drawing above is taken from the original BSA Service Sheet and shows that the chain will, in fact, must always be tight to any 5" tyre slotted in there. With a total width of only 7 inches (178 mm)between the axle plates, and a tyre width of a 5.00 x 16 SM MkII being quoted on the Avon site as 131 mm, the maths is pretty simple (178 - 131)/2 = 23.5 mm per side. I've just measured across the pin on a 5/8" chain and that's a gnat's under 19 mm! Leaves 4.5mm to share between both sides of the chain.
It was never a problem before, none of those pretty back kisses XXXXXX on the side wall any ways up. Even though it had a plunger back end on it then, the chain line has always been the same.Maybe the fellah who lace it back then built it over, an old wheel builder's trick o' the trade mayhap. Who knows now, back then I stuck a tyre on it as quick as I could afford to and slapped it in there. Must have been central enough, got an MOT (safety certificate)........................... in'79!

Snug is good from this day forward...................

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