There's an excellent video on how to adjust valves on the Yamaha TW200, which applies almost verbatim to the Zongshen Sierra, and of course I studied carefully before doing anything.
The take away point, however, was this: instead of second guessing whether you're on TDC right after a compression or an exhaust stroke, just try to feel the valves: they will be very tight/have no play at all if you're on an exhaust stroke (you want to be on a compression stroke). At least that was true for the Yamaha/Yamaha clone engine, but I imagine it's valid for other thumper engines too.
Now, imagine if you "loosened up" your valves while on an exhaust stroke
