Danno said:
One thing I haven't seen mentioned in various threads on Dunstall machines is the headwork. As I remember, Dunstall re-angled the inlet valve for better breathing. It was only a few degrees difference in angle, but apparently produced noticeable gains. Does anyone still do this mod?
The original Dunstall big valve conversion re-angled the inlet by 1.5 degrees, allowing a 1.625" inlet valve. To do so, he had to use the larger intake valve guides, same size as later used by Norton for the 850 engine. Modern conversions to 750 heads typically just use the larger 850 guides. He also did the same mod to 850 heads, but I don't know what size guides he had to use. Larger than the stock 850, but I don't know how much.
Not all the Dunstall Commandos had the big valve head conversion. The '73 catalog lists the Mk 1 "DUNSTALL NORTON 850" as a standard Commando fitted with the Blair exhaust system, with center stand to fit. The Mk 2 was the same, but with ported head (not big valve) and 10:1 CR. The Mk 3 had all the Dunstall glass fibre bodywork, clip-ons, big valve head, Blair exhausts, and 10:1 CR. The Mk 4 had all that plus the Dunstall twin front disk brake system. None of them mention a Dunstall cam, but I'm sure he would have built any of them with it if a customer ordered it.
I don't have as much info on the earlier Dunstall 750 bikes. The ones I've seen had all the glass fibre bits and Dunstall silencers with standard style head pipes. Standard spec was 10:1 pistons, Dunstall cam, and ported heads. You could get the 810 kit and the big valve head as options.
I know he built some 650 and 750 featherbed bikes as "Dunstall Dominators", with café racer styling, and various engine mods as desired, but don't know a lot about them, except that he used a lot of chrome plating! I had a friend many years ago who owned an original Dunstall Dominator 750, but that's the only one I've seen.
Ken