To adjust the valves on a John Deere 4045 engine, remove the rocker arm, crankcase ventilator tube and cover plate. Rotate the flywheel in the clockwise direction until the number one cylinder is at top dead center compression time. Check that the clearance is to specifications, then replace all parts.
Before removing any parts from the engine, disconnect the negative battery terminal to prevent the engine from accidentally starting up. You also want to make sure that the engine is cold before attempting to adjust the valves.
After removing the rocker arm cover and crankcase ventilator tube, visually inspect these parts for wear and tear. After removing the plastic plugs or cover plate from the engine rotation hole, make sure they are removed from the timing pin hole as well.
The engine flywheel is rotated using a JDE83 or JD8-1 flywheel turning tool, while the JDC1571 or JDE81-4 timing pin is used in the flywheel bore. If the number one cylinder rocker arms are loose, then the engine is at number one top dead center compression time, otherwise rotate 360 degrees clockwise.
At number one compression time, the intake valve clearance should be 0.012 to 0.015 inches, while the exhaust clearance should be 0.016 to 0.019 inches. If these are off, loosen the jam nut on the rocker arm's adjusting screw, adjust as necessary, tighten the nut and measure again. Once all clearances are satisfactory, replace the rocker arm cover and crankcase ventilator tube.