The Briggs & Stratton vertical-shaft 12.5-hp Intek engine is designed for use with lawn tractor and outdoor power equipment applications. The engine features a 1-inch-diameter crankshaft, cast-iron sleeve, 3-quart fuel tank and a traditional recoil pull starter. Briggs & Stratton recommends checking and adjusting the engine's valve lash on an annual basis to promote proper engine efficiency and operation. Failure to maintain proper valve adjustment for the engine may result in hard starting conditions and reduced performance.
Place the lawn tractor transaxle in the "Park" position and apply the parking brake, if applicable.
Switch the ignition to the "Off" position and allow the engine to cool before performing any checks or repairs.
Open or remove the bonnet or protective shroud surrounding the engine. Examine the front portion of the engine and disconnect the black spark plug wire from the spark plug, located above the square-shaped valve cover labelled "OHV."
Remove the four bolts securing the valve cover to the cylinder head, using an appropriate size socket wrench.
Examine the exposed portion of the engine valve train. Slowly rotate the engine crankshaft by extending the pull starter rope.
Continue rotating the crankshaft until the bottom rocker arm fully compresses the corresponding valve spring. Grasp the topmost rocker arm to check for play. The rocker arm should be slightly loose at this point.
Check the clearance between the top rocker arm and the corresponding valve stem, located in the centre of the valve spring, using a feeler gauge. If the clearance reading falls outside of the acceptable range of .005- and .007-inch, the top exhaust valve is out of adjustment.
Hold the nut securing the topmost rocker arm to the rocker stud, using an appropriate size metric wrench. Continue holding the nut in position and loosen the small screw located in the centre of the rocker stud nut, using an appropriate size Torx screwdriver.
Insert a ".005" feeler gauge between the top rocker arm and the exhaust valve stem. Rotate the rocker arm stud nut clockwise, while moving the feeler gauge back and forth. Continue tightening the rocker arm nut until you feel a slight resistance when moving the feeler gauge.
Hold the rocker arm nut with a metric wrench. Tighten the centre screw clockwise, using a Torx screwdriver. After tightening the centre screw, remove the feeler gauge from between the rocker arm and valve stem.
Rotate the engine crankshaft using the method described in Step Five. Continue rotating the crankshaft until the topmost rocker arm completely compresses the corresponding valve spring.
Check the clearance between the bottommost rocker arm and valve stem, using a feeler gauge. Perform the adjustment procedure on the bottom intake valve if the clearance reading falls outside of the acceptable range of .003- and .014-inches, using the same methods outlined above.
Replace the valve cover and reinstall the spark plug wire. Lower the bonnet or replace the engine shroud to complete the valve adjustment process.