Sir, am trying to adjust the tappet clearance of Hindustan Tractor 50Hp (4Cylinder) engine,, Some old mechanics suggested to maintain 0.30mm and 0.40mm clearance (Cold)... But when i use that dimension.,, when pistons are TDC am noticing both tappets are still free with some clearance in Overlap.,, i think it is must.,, that both valves should be open in overlap.,, that's why its called overlap. So, if i want valves to be open in overlap time(End of exhaust stroke) and closed at the time of Compression stroke.। Should i reduce clearance from 0.30 mm to 0.10mm??।। If i go above.0.30 mm.। The valves stay closed in Overlap position.