I'm not sure whether you have a B18 or B20 engine. The number will be
cast on the left side of the engine block in letters about an inch high.
If it is a B20, valve lash should be 0.020" or 0.5mm. If it is a B18,
it should be a little less, 0.018" or 0.45mm. It may be a little noisy
set right but don't set it any closer because the valve train expands and
reduces the clearance, and the lack of clearance prevents the exhaust valves
from seating hard enough to transmit heat to the valve seats, and thus
burns the exhaust valves.

The .022-.026" previously cited will reduce horespower very slightly
and increase valve noise a LOT.

Welcome to the board!
--
George Downs Bartlesville, Oklahoma