Briggs and Stratton overhead-valve engines are more efficient than side-valve versions. These engines run at a higher power-to-weight ratio because intake and exhaust gas flow is less turbulent. Apart from that, overhead-valve engines produce more power by operating at a higher compression ratio. This allows for more efficient combustion and better fuel economy. However, because overhead valves are operated with rocker arms resting on pushrods instead of directly onto the camshaft, valve clearances need to be adjusted regularly to ensure smooth operation and to reduce rocker arm and valve stem wear.
- Skill level:
- Moderately Easy
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Things you need
- Socket wrench
- Phillips screwdriver
- .004-inch feeler gauge
Remove the four bolts holding the valve cover to the engine by turning them counterclockwise with a socket wrench. Remove the cover to reveal two pivoting rocker arms with one end resting on the valve stem and the other end resting on the visible end of a pushrod.
Rotate the engine flywheel until the lower push rod has pivoted the rocker arm and pushed its valve inward to the fully open position.
Insert a Phillips screwdriver into the locking screw in the centre of the upper rocker-arm adjustment nut. This nut is situated on the pushrod end of the rocker arm. Loosen the screw by turning it counterclockwise half a turn.
Slide a .004-inch feeler gauge between the other end of the rocker arm and the valve stem. Tighten the adjustment nut clockwise with a wrench while sliding the feeler gauge from side to side until you feel slight resistance. This tells you that the valve clearance is adjusted correctly. Lock the adjusting nut by tightening its central locking screw.
Turn the flywheel until the upper rocker arm has pushed the valve inward to the fully open position. Adjust the lower valve clearance the same way as the upper.
Examine the valve-cover gasket to ensure that it's in good condition. Replace if necessary. Re-install the valve cover by replacing it over the rocker arm opening and tightening the four bolts holding it to the engine.
Tips and warnings
- Warm up the engine before carrying out valve adjustment.
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