At somewhere around 1938 (not sure of the date?) The crankcase was widened to take an extra main bearing and the barrel was widened to include the cooling air gap behind the tappet chest. I think the cylinder head went from 8 to 10 bolts. Ron

email (option): ronpier@talk21.com

Some early military M20s didn't have a sump emptying plug on the underside of the crank cases, not sure when it was added, KM20 or WM20?

Rob

email (option): robmiller11(a)yahoo.co.uk

Thanks all for the information..