I run at a 'snug' .008" on the inlet and a slightly looser .008" on the exhaust...I've done so for years...Weak springs aren't an issue unless they are knackered...Ian
A lot of timing gear clatter is to do with the amount of lash in the cam and pinion gear teeth. At the point were the cam reverts from pushing the valve open to then being pushed by the closing valve, the lash or gap between the teeth changes from one side to the other, resulting in a tap. Apparently at the factory the parts were supposed to have been selected to give the best tolerance fits. I don't know if this always happened or on Friday's all the bad tolerance parts were used up. But in any case, multiple rebuilds over the years could result in a miss match of parts. They seem to happily clatter on happily regardless.
The biggest contributor to engine clatter is when the crankshaft isn't running true within tolerance...Runout of the mainshafts after a crank rebuild should be no more than .002"...
Even slightly larger runouts lead to the crank pinion running eccentrically. That in turn causes alternately too tight and too loose a clearance of the pinion and cam gear teeth and that amplifies the problem detailed in Rons post leading to a lot more clatter...
I've experimented with crank run out and all the other features and it must all be correct to result in an engine that runs mechanically quietly..Ian
And lets not forget cam wear & cam follower wear
BSA put "quietening ramps" on their cams to gently close the cams rather than have them slam shut as you do on race engines
Cams wear over time
