Adjusting valve lash is one of those tasks that no one really enjoys doing, but the every hot-rodder should understand. Valve lash is the distance between the rocker arm tip (roller tip for Erson shaft rockers) and the tip of the valve stem. Too little valve lash will cause the valvetrain to seize up when the engine gets hot and metal starts to expand; too much will cause clattering and eventual valvetrain damage.
Instructions
1. Remove the valve covers and the number one spark plug. Use your factory service manual to identify the number one plug/cylinder; it's usually the driver-side front cylinder on V-configured engines, or the front cylinder on inline engines.
2. Place your finger over the spark plug hole and turn the engine over via the crankshaft bolt. Stop turning the engine when you feel a puff of compressed air try to push your finger out of the hole. Align the top-dead-center (TDC) mark on the harmonic balancer with the pointer on the block. The number one piston is now at top-dead-center. Reinstall the plug and wire.
3. Slide the box-end of the appropriately-sized wrench over the number one cylinder intake valve's rocker adjustment nut. Unlike pedestal rockers, shaft rockers use an adjustment nut located direct over the pushrod. This allows the rocker to pivot in order to take up lash instead of hammering up and down like a pedestal mount.
4. Insert the appropriately-sized Allen head wrench into the hex-hole in the center of the adjustment nut, and turn it one full turn counterclockwise to unlock the adjustment nut.
5. Select the appropriately-sized feeler gauge per your manual specs. The very precise Erson shaft system can typically tolerate about 0.010-inch less lash than factory stamped rockers. Slide the feeler gauge in between the roller tip and valve head, and press the roller tip to the gauge with your thumb.
6. Turn the adjustment nut until the feeler gauge remains snugly pinched between the roller tip and valve. Turn the locking nut clockwise with your Allen head wrench until it is hand tight. Pull the feeler gauge out; the number one intake valve is complete.
7. Move on to the next intake valve in your engine's firing order, and rotate the crankshaft in increments until that cylinder's intake valve is fully closed. For a V8, the next intake valve in the sequence will close with 90 degrees of crankshaft rotation. The next intake valve will close in 33 degrees of rotation for a V6 and every 180 degrees of rotation for a four-cylinder.
8. Adjust the number one exhaust valve after you've finished with all of the intake valves. Repeat Step 2 to confirm that the number one cylinder is back at TDC, and repeat Steps 3 through Step 7 to adjust the exhaust valves. Reinstall the valve covers and allow the engine to idle for 10 minutes to bring it up to temperature. Re-check the valve lash on two intake and two exhaust valves to ensure that it is within the hot-lash specs for your engine.
