Is the standard chain length not shown in the workshop manual ? WD Nortons with 18t engine and 42t clutch ran a 74 link primary...but every Renold chain spare parts tin included cranked half links. If you use one though, fit in the correct direction (so that it pulls together rather than apart).
Yes Rik. The standard WD 19T engine sprocket was fitted with a 69 link primary chain. Since I upgraded my engine to 600cc, I fitted a 20T sprocket and a 70 link chain. A 21T sprocket would require a 71 link chain.
I tried a 21T sprocket but found it to tall for my liking, so went back to the 20T. Ron