How to Adjust a Valve Lash on a Chevy 350 CID Engine

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Most production Chevrolet 350ci engines are equipped with hydraulic tappet (lifter) camshafts that do not need adjustment except in the case of a significant disassembly or reassembly. In this case, an initial adjustment is typically all that is required. However, if the engine is equipped with a mechanical tappet cam, then the procedure varies a bit.

Things You'll Need

  • Assorted small SAE sockets\n3/8- and 1/2-inch drive socket wrench\nAllen driver or wrench\nFeeler gauges\nRemote starter switch (optional)\nPen and paper

Hydraulic Tappet Camshafts

  • Adjust the “pre-load” with the following procedure (engine OFF, valve covers removed):\n\nPlace a socket and wrench on the crankshaft bolt or snout, and rotate the engine clockwise until the No. 1 piston is at top dead center (TDC). (The No. 1 cylinder is the driver’s side front cylinder.)

  • Tighten the rocker nut on the No. 2 cylinder INTAKE rocker arm with a socket wrench while rotating the pushrod between your index finger and thumb until the pushrod becomes just difficult to rotate. The valve is now at zero-lash, but the lifter is not yet pre-loaded.\n\n(Hydraulic lifters are designed so that the lifter itself provides the take-up of any lash. As a result, they have a spring and oil pressurized plunger within them that needs to be “pre-loaded.”)\n\nRepeat this procedure with the No. 7 INTAKE and No. 4 and No. 8 EXHAUST rocker arms.\n\nRotate the crankshaft clockwise precisely 180 degrees. Repeat the procedure for INTAKE rocker arms No. 1 and No. 8, and EXHAUST rockers No. 3 and No. 6.\n\nRotate another 180 degrees and set INTAKES Nos. 3 and 4 and EXHAUST rockers Nos. 5 and 7.\n\nAfter rotating the final 180 degrees (two complete rotations of the crank), set the Nos. 5 and 6 INTAKES and the Nos. 1 and 2 EXHAUST valves.

  • Tighten each of the 16 rocker nuts an additional ¼ to ½ turn or as recommended by the cam manufacturer. The lifter plungers are now pre-loaded, and the lash should be correctly set. Reinstall the valve covers, clear the tools and start the engine to check results.

Mechanical Tappet Camshafts

  • Rotate the engine with a crank socket until the No. 1 cylinder’s INTAKE valve fully opens and then just begins to close. Insert a feeler gauge into the lash area of the No. 1 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 the rocker nut to gain the recommended clearance. (Log each valve's initial and final lash by cylinder and valve on paper.) \n\nNote: Some rocker arm nuts have an Allen set-screw. This set-screw must be loosened before adjusting the nut to gain proper valve lash, then tightened afterward.

  • Rotate the crankshaft so that now the No. 1 EXHAUST valve just begins to open. Repeat Step 1 for the No. 1 INTAKE valve, logging the initial 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.

  • Recheck valve lash clearances after several hot/cold/hot operating cycles, carefully checking clearances when the engine is hot. Use the same sequences as above. You may find clearances are wider than initially set (and logged) in your notebook. This is normal at operating temps. Note the differences--if any--and reduce the clearances, if excessive. Adjust the cold-lash values in the log book down by a similar amount they were loose while hot. This permits the correct lashing of valves next time while the engine is not at operating temperatures.

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