A purpose machined flywheel is required. The friction face should be a good quality close grained Cast Iron or Steel (0.35 / 0.45% Carbon, Hardness 200 Hb minimum), with a surface finish of 0.75µm RA (30 CLA) maximum.
Run out when assembled to the crankshaft must not exceed 0.08mm (0.003") maximum at 77mm (3.03") radius. Fixing holes and location spigot to be machined as shown on the appropriate flywheel mounting drawings.
N.B. Cast Iron flywheels should not be used above 10000 rpm.