[Nviduum]

Hmmm... maybe you should take a look at the valve's clearance (to control when engines hot) this should be about 0.15mm for the intake and 0.35mm for the exaust valves. In case of clearence's mismatch take a good look at the camshaft for abrasive wear. If the clearence's mismatch is in a extreme range (no clearance at all) you should take of the rocker arms and control them for wear too. For the screw's torque I will take a look at the Repair manual.