BSA Crankshafts

All BSA crankshafts are machined, welded, ground, balanced and nitride heat treated for extra strength and wear resistance. A new flywheel replaces the original flywheel. Crankshaft customers must supply weight of one piston with rings, wrist pin and cir-clips.  They must also identify the connecting rods they plan to use (stock or other). The customer is responsible for making sure that each piston weighs the same amount.  The drive side journal is offset 90° behind the timing side journal, in the direction of crank rotation, to match camshafts sold by SRM Classic Bikes.

The BSA timing side journal can be ground to stock size or modified to suit a roller bearing.  Timing-side conversions are done by firms such as SRM or British Cycle Supply.  If not building a racer, or very large displacement BSA engine, we recommend using stock timing side bushing and a high-pressure oil pump.  The later style 1.500″ timing side bushing is required for A10 engines to replace original 1.375″ bushing used on earlier (pre-1958) crankshafts.  An oil filter must be used with an offset crankshaft as stock sludge trap is removed.  All cranks are lighter then stock so they have less inertial weight for faster acceleration.  A65 and A10 crankshafts are balanced to 50% unless another balance factor is specified by customer.  The higher the RPM range where a desired smoothness is required the lower the balance factor number.  A racing engine may use a balance factor of 45% for best smoothness above 5000 rpm but it will vibrate below 3000 rpm.  A balance factor of 45% is used for best smoothness above 6000 rpm

All 76 degree cranks cost $200 USD more than quoted prices quoted with each crankshaft type.

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