Small Engines (Lawn Mowers, etc.): piston to valve settings, compression stroke, power stroke

Question
               
       hello ,
    how would you set one piston to two valves
  (ohv) when the piston is on it's up stroke
    should the intake valve already be closed or
  open at the time of the piston up stroke
  ( or combustion stroke )
              thank you for all your help
                 warren

Answer
Hi Warren,

The intake and exhaust valves are closed on the piston's upward compression stroke and through the downward power stroke.  The exhaust valve opens on the upward 3rd stroke and the intake opens on the downward 4th stroke.

Best,
Michael