S30 Valve Adjustment

Specs

The factory service manuals give the same clearances for the L24 (1972 manual) and the L28 (1975 and 1976 manuals). The final setting is the warm one; the cold numbers are only for getting a rebuilt engine started.

The manuals list the exact values as 0.0098" and 0.0118" warm, and 0.0079" and 0.0098" cold, which round to the feeler gauge sizes above. Nissan's pivot adjuster tool for the lock nut is ST10640001. Firing order is 1-5-3-6-2-4, with No. 1 at the front.

Tools

• Feeler gauges in 0.008", 0.010" and 0.012". Straight blades are easiest; a bent "go/no-go" set also works.
• 14mm wrench for the pivot (the adjuster) and 17mm wrench for the lock nut. The two wrenches crowd each other, which is why many people grind one down thin or buy a valve adjusting tool made for L-series engines.
• A socket and breaker bar on the crank pulley bolt to turn the engine, or a remote starter switch.
• A new valve cover gasket if the old one is hard or torn.

How It Works

There are 12 valves and 12 rocker arms, numbered 1 to 12 from the front of the engine. Each rocker arm sits under the camshaft: one end rides on the ball-shaped pivot, the other end pushes on the valve stem through a lash pad, and the cam lobe presses down on the middle. The clearance is the gap between the cam and the rocker arm when the lobe is pointing away from the rocker, straight up.

Turning the pivot (14mm) raises or lowers the rocker arm. Raising the pivot closes the gap; lowering it opens the gap. The lock nut (17mm) holds the pivot where you set it.

Valve Order, Front to Rear

The valves run E-I-I-E-E-I-I-E-E-I-I-E: exhaust valves are at both ends and in pairs, intake valves are in pairs. Use the intake gauge on the I valves and the exhaust gauge on the E valves.

Step by Step

1. Warm the engine up to normal operating temperature, then shut it off. The manual says the clearance can't be adjusted with the engine running.
2. Remove the valve cover. On a 280Z, unclip or move the hoses and wiring on top first. Pull the spark plugs if you'll be turning the engine by hand; it makes it much easier.
3. Turn the engine clockwise (the normal direction of rotation) with the crank bolt until the lobe for the valve you're checking points straight up, away from its rocker arm.
4. Check the gap by sliding the feeler gauge between the cam lobe and the rocker arm pad. It should slide through with a light drag. Check every valve at the same spot.
5. Adjust if needed. Hold the 14mm pivot, loosen the 17mm lock nut, then turn the pivot until the gauge has a light drag.
6. Lock it. Hold the pivot still with the 14mm wrench while you tighten the lock nut to 36 to 43 ft-lb. Tightening the lock nut tends to drag the pivot and close the gap, so recheck with the gauge every time.
7. Repeat for all 12 valves. You need two full turns of the crankshaft (one turn of the camshaft) to bring every lobe up.
8. Recheck hot. If you set the valves cold after a rebuild, run the engine for several minutes and check them again at the warm specs, as the manual says.
9. Clean up. Remove any tool from the crank bolt before starting the engine, then reinstall the valve cover.

Watch It Done

Restoration For Beginners walks through adjusting the valve lash on an L-series engine:

Video: Datsun L-Series Engine Testing and Tuning Ep.5 Adjusting Valve Lash by Restoration For Beginners

A Faster Sequence

You don't have to go one valve at a time. When one lobe is straight up, several others are also on the back of their lobes and can be checked at the same time. This cheat sheet, shared on the VicZcar forums, sets all 12 valves in four stops:

If you're not sure, the one-lobe-up method in the steps above always works. A different cam or a mismatched cam timing can change which lobes line up.

Common Problems

• The gap changes when you tighten the lock nut. Keep the 14mm wrench on the pivot while you tighten, and recheck afterward.
• A valve keeps getting tighter, or the pivot is already screwed all the way down and the gap is still too small. The valve has probably sunk into its seat, usually an exhaust valve. The head needs a valve job.
• Ticking after adjustment. Recheck the gap on the noisy cylinder, and look at the rocker arm and cam lobe for wear. A worn cam or rocker pad makes the gap hard to measure and comes back quickly.
• Refitting a rocker arm means pushing the valve spring down. Make sure that cylinder's piston isn't at top dead center first, or the valve can hit the piston and bend.
• Pivot near the end of its travel after a cam change or valve job. The lash pads are probably the wrong thickness; see Lash Pads.

Lash Pads

A lash pad is a small hardened cap that sits on the tip of each valve stem, where the rocker arm presses on it. Its thickness sets the rocker arm geometry: the angle the rocker sits at and where the cam lobe rides on the rocker pad. With the stock cam and a stock head you never need to think about them, but a reground cam (which has a smaller base circle), a valve job that sinks the valves, or new valves with a different stem length can all call for a different thickness.

• Stock size: about 0.120" thick. Genuine Nissan standard pads are still sold as NOS.
• How many: 12 for an L24, L26 or L28 (one per valve), and 8 for the four-cylinder L16, L18 and L20B.
• Checking the size: look at the shiny wipe pattern the cam lobe leaves on the rocker arm pad. It should be centered and not run off the pad. If it sits toward the valve end of the rocker, use a thinner pad; if it sits toward the pivot end, use a thicker one.
• The pivot as a clue: if a pivot has to be screwed nearly all the way out or all the way in to get the right clearance, the geometry is off and the pad thickness is worth checking.