Some performance engines have mechanical camshafts with solid tappets. Most production big block Chevy engines have hydraulic lifters. The difference between the two is that hydraulic lifters are set so that there is no clearance between the tip of the valve and the end of the rocker arm, but solid lifter-type camshafts are designed so that there is a small amount of clearance. This amount is small--typically around .020 inch--and is call valve lash. Valve lash should be checked periodically and adjusted, if necessary.
- Skill level:
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Things you need
- Small container to store fasteners
- Wheel chocks
- Valve cover gaskets
- Assorted small SAE sockets
- 3/8- and 1/2-inch drive socket wrench
- Allen driver or wrench
- Feeler gauges
- Remote starter switch (optional)
- Pen and paper
Start the car and bring it to normal operating temperature. The valvetrain must be hot to accurately set the valves to hot-lash specifications.
Turn the car off and ensure that it can not move. Place the transmission in park or in low gear (if a manual transmission) and engage the emergency brake. Small "chocks" in front and behind one tire are a good safety idea.
Release the bonnet latch, raise the bonnet and organise the tools so that they are easily accessible. If there is room along the front radiator support, this can be a good place to set tools or a tool tray. Place a protective blanket on painted surfaces to prevent scratching or marring.
Attach the wire end clips for the remote starter switch to the starter and feed the switch up (from below) to the side of the engine you will be working on. Ensure there is no electrical power to the ignition system before engaging the switch. Alternatively, turn the engine over from the crankshaft snout with a wrench.
Locate any hoses and wires that are attached to or running along or over the valve covers. Disconnect and set them aside, out of the way. Identify the valve cover bolts, and use the proper size socket to remove them. Set them safely aside in a container. Lift the valve cover off and set it aside.
Bump-turn the engine over with the remote starter until the intake valve opens then begins closing. Insert a feeler gauge into the lash area of the EXHAUST valve. Make note of the feeler gauge size that offers movement in and out, but with slight interference. If it's not at recommended specs, loosen or tighten to the recommended specifications by turning the rocker nut. (Log each valve's initial and final lash by cylinder and valve on paper.)
Note: Some rocker arm nuts have an Allen setscrew. This setscrew must be loosened before adjusting the nut to gain proper valve lash, then tightened afterward.
Bump-start the engine over so that now the exhaust valve begins to open. Repeat Step 4 for the intake valve, logging the initial and adjusted lash accordingly. Repeat for the remaining cylinders and double check that all rocker nuts are secure. Reinstall the valve covers and wires/hoses. Prepare the car for operation and test drive.
Tips and warnings
- After operating the engine through several hot/cold cycles, check the lash cold to get a good baseline of what the cold-lash clearances should be in the future. Use the same “intake-closing, exhaust-opening” sequence and log cold-lash clearance values in the journal. This serves to keep from having to perform the service on a hot engine in the future as long as the same valvetrain is used.
- DO NOT permit a mechanical camshaft to operate with no clearance. Engine damage may occur. Also, abnormal clearances are also and indicator of potential problems and should NOT be ignored.
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