Hello Andy , There is a quick way of checking the valve timing,
Take the spark plugs out and the valve caps off, If a valve is open the adjuster can jam the cap from coming off, So turn the engine over a small amount, You probably know this , Sorry,
Turn the engine over via the rear wheel in second gear till what ever cylinder you want to check is at TDC
On NOT the firing stroke, Both valves should be open the same amount, ie Rocking at TDC,
One going down and the other going up,
You should be able to see the top of the piston though the plug hole,
Maybe get a friend to rock the rear wheel back and forth ? a small amount.
Good Luck, Bill.