The clearance rule that I go with is kind of a 60 / 100 rule. Typically you want 0.060" clearance between the intake valve and the piston and 0.100" clearance for the exhaust valve. As far as the valve spring, clearance before coil bind, 0.060" is a good number, and you want to make sure that you have around 0.090" of clearance between the valve spring retainer and the top of the valve guide.
Most of my engine building experience has been with the air cooled VWs (30 years) and dirt bikes, and these guidelines have served me well (not for 2 stroke though  .). The A12 is a fairly mild grind, so if you can get your numbers in these ball parks, you should be fine.
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2005 Hammerhead 150
170cc BBK, PnP Big valve Head, A12 Cam, Uni Filter, Custom Exhaust, 10G rollers, 1500 Contra Spring, 2000 Clutch Springs
Just added - 2007 Joyner 250 SV - Let the fun begin
4-Dirt Bikes, Baja Bug and enough toys to keep me in the garage and out of trouble.
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