Valve adjustment.

This was still one of those seemingly trivial things left to do before I start the engine.
I have done this many times before on the Commando, as well as on other venerable OHV engines; but there is never a time when you can assume it will all go smoothly just because you've done it before: as I was rotating the engine (4th gear engaged, sparking plugs out, slowly rotating the rear wheel) I heard this sickening "t-KLANG!" and knew something was wrong.
Still, everything looked normal, and all four valves were opening and closing as you'd expect, so I proceeded to set the clearance as per the workshop manual: Inlet .006in. [0.15mm] and Exhaust .008in. [0.20mm].
However, when I came to the exhaust valve for cylinder 1, there was basically zero clearance between the rocker and the valve stem. Odd... how could this be? After all everything appeared to be in place.
Well it turns out that the rocker ball-end was not seated in the pushrod cup, but was pressing on its edge instead! Hence no clearance, it was simply too far up. So, rather than try to leverage the pushrod back in place and risk damaging it (unacceptable at this stage), I took the bloody rocker out and refitted it.

This was made much easier thanks to Thomasdunstall! Thanks Mario!

He's holding the pushrod in place using a very special tool... a piece of wire with a shepherd's hook at one end.

The good news is that with everything correctly back in place there was plenty of room to set valve clearance, and we are miles away from potential coilbound disaster when the valves are fully open, though of course I'll double and triple check that before I start the engine. That means that fitting heat insulating washers under all valves was a "gamble" that paid off, and I now have peace of mind of knowing that they're there, hopefully making my springs last a little longer.
Of course if you don't at least bust a knuckle, you're not doing it right.