I think orabanda's mag body bolt hole slotting is the best remedy.
I agree - for machines with a 'long nut' lower fastener for the mag. No help on those which use a nut and bolt inserted behind timing gear or sprocket though sadly.
There have been loads of efforts to make it easier to retime and / or adjust over the years - Rex' Ariel thing, Panthers, lots of older continental efforts, various couplings on cars, use of keyed drive components and so on. End of the day, it's just one of those jobs, but it would be great if there were easy ways of fine tuning to find the sweetest spot on full advance, without upsetting the internal settings of a mag. Playing with alloy head As is a case in point, given their propensity to pink on book settings quite commonly, but it is also relevant in terms of suiting fuel quality. Me, I tend to go for a couple of degrees less max advance than book for starters, and see how it goes.
Orabanda's older post about dynamometer testing various As is always at the back of my mind, where he showed that less advance was helpful in terms of power and torque in some cases. The variations specified between similar engines of similar design is really quite large, from the Very Big Numbers on Trihards and AMC twins to the more reasonable figures on Notruns, some of which run best at 28-30°, via Beesas somewhere in between. I always understood, rightly or wrongly, that the need for massive advance spoke to inherent design flaws, but WTHDIK.
