This is the front plain primary gear bush(not the top hat one) that needs to be reamed after replacing. This is costly so with modern technology we have produced a floating bush that fits straight in the hole when the original is removed. The part number for this bush is C-AEA3240.

The finished sizes of the bushes are –

For road use;

Front bush 1.628″ +0.002″, rear bush 1.503″ +0.002″.

For race use;

Front bush 1.631″ +0.002″, rear bush 1.504″ +0.001″.

NOTE: these figures are based on the crankshaft surfaces where the primary gear runs being ‘as new’ in sizing. If the crankshaft is well used and shows signs of wear in these areas – carefully measure the journal diameters with a micrometer (or some such suitably accurate device). To the figures gained allow a running tolerance of 0.003″ – 0.005″ for road use on both bushes, and 0.006″ – 0.008″ on the front bush, 0.004″ – 0.005″ on the rear bush for race use.

Running clearance for this gear-front bush running clearance finished size 1.503″ +0.002″-0-0″

For race use 1 thou more clearance with plus 1 thou tolerance but never undersize.

Front bush 1.628″ +0.002″ -0.0″ never undersize as it requires clearance.

For race allow an extra thou 1.504″ +0.001″ only.

if cranks are worn measure crank and allow 3-5 thou running clearance and race use 5-7 thou on front bush and 4-5 thou on rear bush.