Crank rebuild


Any competent workshop should be able to do a crankshaft rebuild, here is a crankshaft completely disassembled and ready to be rebuilt.

The whole process begins by completely disassembling the crankshaft and cleaning everything. The crank pictured above will be a 270 rephase which explains the splined shaft and additional internally splined crank flywheel. As you can see the flywheel on the right has been modified by machining the bearing mount down to the width of the bearing plus 1mm. The flywheel on the left is unmodified and still has the cut-out for the cam chain sprocket to key into.

All new bearings and connecting rods would be used in the assembly as required.

All the component parts are then pressed together with the correct clearances on the big end of the conrod.

Once the assembly is completed it is adjusted for correct alignment.

Here are the tolerances required by Yamaha for the XS650 crankshaft.

Here is a picture of the modified crankshaft we are using in our club racer which has been lightened and polished and was assembled and welded by Daryl Hutcheon.

This procedure is followed for all crank rebuilds except welding is not always required on a stock rebuild, it is however highly recommended for all rephased crankshafts.