In the past we have made one piece `billet` cranks but found zero gain on the dyno or on the track & the difficulty in balancing the cranks for a variety of engine configurations was a nightmare. We have a variety of different flywheels to match up with the different crank cheeks to get a good balance factor. With the very high price of a one piece crankshaft, and with no improvements in performance, it makes absolutely no sense in engineering terms to build one that way.
Our experience is that the lighter the crank of a Norton Twin, the better the engine is, and thus improving both acceleration and braking. Our 89mm stroke cranks are just over 20 pounds weight (9.4kg) which is the lightest that can be produced whilst achieving our desired balance factor of 75% for rigidly mounted engines. If you are planning to mount the engine in an "Isolastic" chassis, the balance factor needs to be reduced to 52% & this should be notified at the time of ordering.
Do know that our crankshafts are built to `Pre Mk3` Commando specifications and dimensions. They can be used in Dominator, 650ss, Atlas, N15, G15 & Commando cases, but not Mk3. Due to the fact that these cranks are machined all over, the dynamic balance is improved compared with standard cranks. Balance factor assumes stock rods & pistons.
If desired, we can dynamically balance the crank to suit your exact piston and rod combination but this requires precise weights from you (or the actual components) and is subject to additional cost. Currently, we offer 80.4mm (750 Short Shroke), 89mm and 93mm (for 1000cc engines) stroke cranks, but the range may expand in the future. For enquiries, please contact me at Britironclassics@gmail.com.