I ground out the inlet valve guide flush with the inlet tract, radiused the top of the barrel to get better flow into the bore and had the head cast iron welded and then polished to the same contours as the SWD Big 4 as both machines run an 82mm bore. Run with an AMAL 389 Monoblock. A number of Gold Star cams were tried previously but no perceptible improvement in performance. Double valve springs used to both valves - I think the C.10 springs will sit easily inside the M.20 /21 springs.

Have not lightened the flywheels. Have run with a set of BSA MCR gearbox internals, lucas racing mag.

A lot of relatively inexpensive opportunities to improve the performance of what was considered to be grey porridge compared to fettling something exotic out of which you may not get much in the way of a reward.

Having said that didn't Harley Davidson say you cannot beat cubes?