The valves on a Briggs & Stratton engine control the flow of fuel and air into the engine, and exhaust out of the engine. Improperly adjusted valves can cause a variety of problems, including loss of power, stalling, excessive fuel consumption and backfire. With some basic tools and a little mechanical aptitude, you can adjust the valve lash on a Briggs & Stratton engine in about an hour. The procedure for valve adjustment varies by model, but the basic steps are the same for all Briggs & Stratton engines.
Disconnect the rubber cap that connects the spark plug to the magneto. Use a socket wrench to loosen the spark plug and remove it from the engine cylinder.
Remove the screws holding the plastic cover on top of the engine. Lift the cover up and turn it to the side, being careful not to kink or break the fuel lines. Remove the air cleaner housing, carburetor, muffler, and any other components blocking access to the cylinder head. This varies by model; some models require you to remove all of these components from the engine, while other models do not require you to remove any of them. Remove the rocker cover screws and pull the cover off to reveal the valves.
Turn the flywheel by hand until both valves are closed and the piston is at top dead center. Insert a plug into the spark plug hole until it contacts the piston. Make a mark on the pin with the edge of the spark plug hole. Turn the flywheel until the piston is at its lowest point. Make another mark on the pin. Turn the flywheel until the valves are closed and the piston is at top dead center.
Measure the distance between the two marks on the dowel pin. Make another mark on the dowel that is a quarter of the distance from the first mark to the second mark. Insert the plug into the spark plug hole and rotate the flywheel past top dead center until the third mark on the plug is even with the spark plug hole.
Consult the manufacturer’s literature to determine the correct valve clearance for your engine. Slide a feeler gauge to measure the correct valve clearance thickness between the swing arm and valve head.
Hold the rocker arm nut with an open end wrench. Loosen the set screw of the rocker arm nut with a head star driver. Turn the rocker arm nut clockwise to decrease valve clearance and counterclockwise to increase valve clearance. Adjust the rocker arm nut until the gauge slides between the rocker arm and valve head with slight resistance. Tighten the set screw to the correct torque using a torque wrench with a star bit to set the valve clearance. Adjust the other valve using the same procedure.
Place the rocker cover on the cylinder head and bolt it in place. Install any components you removed to get to the cylinder head. Place the plastic cover over the engine and install the retaining screws. Screw the spark plug into the cylinder head and tighten securely. Place the spark plug bushing on the end of the plug and snap it into place.
Tips
Use new gaskets when reassembling the rocker cover and any other removed components. Check the removed components for wear or damage. Replace any parts that look suspect. For V-Twin engines, perform valve adjustment on both cylinders.
Warnings
You should only perform a valve adjustment on a cold engine. Be careful not to damage or break the rocker bolt or set screw.