Adjusting the Valve Lash on a Snowblower

This video from Sears PartsDirect shows how to adjust the valve lash on a snowblower. The valve lash is the amount of clearance between the top of the valve stem and the rocker arm. Incorrect valve lash prevents the valve from opening or closing properly. The engine will be hard to start, run poorly and lose power when valve lash is incorrect. Premature valve failure also results from improper valve lash. Check valve lash after the first 25 hours of use and then every 100 hours.

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Rocker Cover Gasket

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Before you begin, allow the engine to cool. Wear work gloves to protect your hands. Disconnect the spark plug wire. Use a deep socket and a ratchet to remove the spark plug from the cylinder. Place a shop towel under the rocker cover to catch oil. Remove the 4 rocker arm cover screws. Squeeze the breather hose clamp and pull the hose off the rocker cover. Remove the rocker cover. Insert a 12-inch wooden dowel into the spark plug hole and rest it on top of the piston. Slowly pull the starter rope to cycle both valves and reach the compression stroke. You’ll know you’ve reached the compression stroke when both valves are closed and the piston is moving up, which will push the dowel away from the engine. Continue to pull the starter rope until the dowel reaches its full extension out of the spark plug hole. Both valves will be closed and both rocker arms will be slightly loose when the piston is at top dead center on the compression stroke. Insert the feeler gauge between the intake rocker arm and valve stem to measure valve lash clearance. The intake valve is on the carburetor side of the engine. Intake valve lash clearance should be .003-inch to .005-inch on this engine. Repeat the measurement process for the exhaust valve on the muffler side of the engine. The exhaust valve lash clearance should be .005-inch to .007-inch. Loosen the jam nut while holding the fulcrum nut stationary with a wrench. Turn the rocker arm fulcrum nut clockwise to decrease the interior valve lash clearance or counterclockwise to increase it. Once you reach the proper valve lash clearance, hold the rocker arm fulcrum nut stationary with a wrench and tighten the jam nut to 80- to 106- inch-pounds using a torque wrench. Recheck the valve lash clearance after tightening the jam nut. Adjust the valve lash clearance on the exhaust valve if needed. Rotate the engine through several compression cycles. Return the piston to top dead center of the compression stroke. Recheck the valve lash clearance and adjust the valves again if necessary. Clean up oil around the rocker arms. Examine the rocker cover gasket and replace it if damaged. With the gasket pressed into the rocker cover, reinstall the rocker cover on the engine. Tighten the rocker cover screws to 62- to 80-inch-pounds using a torque wrench. Reattach the breather hose and secure it using the hose clamp. Warning: Overtightening the rocker cover screws could cause an oil leak between the rocker cover and cylinder head. Thread the spark plug into the cylinder and tighten it using the deep socket and ratchet. Reconnect the spark plug wire.



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