The Kohler Command engine, frequently found in lawn tractors, zero-turn mowers, and other small engine applications, relies on properly adjusted hydraulic valves for optimal performance. When valve lash is incorrect, it can lead to reduced power, increased fuel consumption, rough idling, and even engine damage. While the hydraulic lifters are designed to maintain zero lash, periodic checks and adjustments are still necessary, especially as the engine ages.
Preparing for the Adjustment
Begin by gathering the necessary tools. You will need a socket set (metric sizes are common), a torque wrench, a feeler gauge set (specifically including a thin gauge for checking lifter preload), a valve spring compressor tool (specifically designed for small engines), and the engine's service manual. Cleanliness is crucial; use a clean workbench and shop rags to prevent dirt from entering the engine. Let the engine cool down completely before starting. Working on a hot engine can cause burns and inaccurate measurements.
Consult the service manual for the specific valve lash specification for your Kohler Command engine model. These specifications are critical for achieving the correct adjustment. Disconnect the spark plug wires to prevent accidental starting during the procedure. Remove any shrouds, covers, or other components that obstruct access to the valve covers. Identify the cylinder you'll be working on. Typically, small engines have one or two cylinders. Refer to the engine's documentation to determine the cylinder numbering convention.
Locate Top Dead Center (TDC) on the compression stroke for the cylinder you're adjusting. Rotate the engine by hand, using a socket on the crankshaft pulley or flywheel nut. Place a screwdriver or other probe into the spark plug hole of the cylinder you're working on. As you rotate the engine, observe the movement of the piston. When the piston reaches its highest point, you're near TDC.
To confirm you are on the compression stroke, check the valve rocker arms. At TDC on the compression stroke, both intake and exhaust valves for that cylinder should be closed, and the rocker arms will have some free play. If the valves are opening or closing as the piston reaches the top, you're likely at TDC on the exhaust stroke. Rotate the engine one full revolution (360 degrees) to reach TDC on the compression stroke. Align the timing marks on the crankshaft pulley or flywheel with the corresponding marks on the engine block. This ensures accurate TDC positioning.
Adjusting the Valve Lash
With the engine at TDC on the compression stroke for the first cylinder, use the valve spring compressor to compress the valve spring of the intake valve. This will allow you to remove the rocker arm. Inspect the rocker arm for wear or damage. Replace it if necessary. Loosen the rocker arm adjustment nut. Insert the specified feeler gauge between the valve stem and the rocker arm. Tighten the adjustment nut until you feel a slight drag on the feeler gauge. Use the torque wrench to tighten the adjustment nut to the torque specification listed in the service manual. This is crucial for preventing loosening and ensuring proper valve lash.
Repeat the process for the exhaust valve on the same cylinder. Remember to compress the valve spring, remove the rocker arm, check for wear, loosen the adjustment nut, insert the feeler gauge, tighten the nut until you feel slight drag, and then torque the nut to the specified value.
After adjusting both valves on the first cylinder, rotate the engine one full revolution (360 degrees) to bring the other cylinder to TDC on the compression stroke. Repeat the entire adjustment process for the second cylinder, ensuring you follow the same steps for both intake and exhaust valves.
Checking Hydraulic Lifter Preload
Kohler Command engines use hydraulic lifters, which require a specific preload. After adjusting the valve lash as described above, check the lifter preload. The service manual specifies this measurement, typically expressed as a range (e.g., 0.002-0.004 inches). To check preload, use a thin feeler gauge set. Attempt to insert the specified feeler gauge between the rocker arm and the valve stem with the adjustment nut torqued to the correct specification. If you can insert a feeler gauge thicker than the maximum preload specification, the preload is too loose. If you cannot insert a feeler gauge even thinner than the minimum specification, the preload is too tight.
If the preload is incorrect, you may need to replace the hydraulic lifter. Incorrect preload can indicate a worn or damaged lifter that is not properly compensating for valve train expansion. In some cases, very slight adjustments to the rocker arm nut might bring the preload within the acceptable range, but this should only be done with caution and in accordance with the service manual.
Final Steps and Verification
After adjusting all valves and checking the lifter preload, reassemble the engine. Reinstall the valve covers, shrouds, and any other components that were removed. Reconnect the spark plug wires. Start the engine and listen carefully for any unusual noises, such as valve clatter or ticking. Allow the engine to run for a few minutes to allow the hydraulic lifters to fully pump up. If you hear unusual noises, recheck the valve lash and lifter preload.
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Verify the engine's performance. Check for smooth idling, proper acceleration, and adequate power output. If you experience any issues, such as reduced power or rough running, re-evaluate the valve adjustment and other potential causes, such as carburetor problems or ignition issues.
Proper valve adjustment on a Kohler Command engine requires patience, precision, and adherence to the service manual specifications. By following these steps carefully, you can ensure optimal engine performance and longevity.
Practical Tips
Keep the service manual handy: The service manual is your most valuable resource. Always refer to it for specific torque values, valve lash specifications, and other critical information.
Invest in quality tools: Using high-quality tools will make the job easier and prevent damage to the engine. A good torque wrench is essential for achieving accurate adjustment.
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Cleanliness is key: Dirt and debris can damage engine components. Work in a clean environment and keep all parts clean.
Don't rush: Take your time and double-check your work. Rushing can lead to errors that can cause engine damage.
Replace worn parts: If you find any worn or damaged parts, such as rocker arms or hydraulic lifters, replace them immediately. This will prevent further damage and ensure optimal performance.
Troubleshooting
Engine runs rough: Check the valve lash and lifter preload. Also, inspect the spark plugs, carburetor, and ignition system.
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Engine lacks power: Valve lash may be too tight. Recheck the adjustment.
Valve clatter: Valve lash may be too loose. Recheck the adjustment.
Difficulty starting: Improper valve timing can make starting difficult. Ensure the engine is at TDC on the compression stroke when adjusting the valves.
