Setting valve clearance: 250 with screw adjusters

[bikester250]

This is probably a stupid question but here goes.
The Clymer reprint says to set valve clearance with the piston at TDC and a cold engine. Some of my Brit bikes set the clearance with the opposite valve open (i.e. set the exhaust when the intake is open).
I've been fiddling around and noticed that the clearances are larger if I check them this way instead of at TDC. The difference is around 0.003". Any thoughts out there on this?
Thanks, Phil

[double diamond]

If you set clearance with one of the valves open, this means the rocker arm of the open valve is pushing down on the cam. This takes up any clearance in the cam bearing at the lower (6 o’clock) position and leaves more clearance at the upper part (12 o’clock position). At TDC on the compression stroke, both valves are closed so the cam is not being pushed down by the rocker arm. The .003” you observe is the clearance/wear in the cam bearing. Matt