screw in the rocker arm, as shown in figure 3-74. On engines with stud-mounted rocker arms, make the adjustment by turning the stud nut.

Valves in Block

This type of valve arrangement is not commonly seen in the field; however, the adjustment procedure is described in case you should happen to run across this type.

Valves within the block are adjusted

"COLD"; that is, recommended valve clearances are provided for a cold engine. These valves have mechanisms quite similar to overhead valves. They are adjusted by removing the side cover plate beneath the intake manifold on the side of the engine block (fig. 3-75). Since you must stop the engine to adjust the valves, the piston in the cylinder must be on TDC of the compression stroke. You can determine this by watching the valves of the piston that is paired with the one that is being set. As the cylinder that is being positioned is coming up on the compression stroke, the paired cylinder is coming up on the exhaust stroke; therefore, the exhaust valve is open. Just as the exhaust valve closed and the intake valve begins to open, the cylinder to be set is on TDC of the compression stroke, and you can set the two valves. Once the No. 1 cylinder is positioned, follow through according to the firing

Figure 3-74. - Adjusting overhead valves.

Figure 3-75. - Adjusting valve in block.

order of the engine, as this makes the job easier and faster. You may also use this procedure when adjusting valves on overhead engines.

Hydraulically Operated Valves

On engines with hydraulic valve lifters, it is not necessary to adjust the valve periodically. The engine lubrication system supplies a flow of oil to the lifters at all times. These hydraulic lifters operate at zero clearance and compensate for changes in engine temperature, adapt automatically for minor wear at various points, and provide ideal valve timing.

To adjust hydraulic lifters with the engine off, turn the crankshaft until the lifter is on the camshaft base circle (not the lobe). The valve must be fully closed. Loosen the adjusting nut until you can wiggle the pushrod up and down. Then slowly tighten the rocker until all play is out of the valve train (cannot wiggle pushrod). Repeat the adjusting procedure on the other rockers.

To adjust hydraulic lifters with the engine running, install a special oil shroud or some other device for catching oil spray off the rocker. Start and run the engine until it reaches operating temperature. Tighten all rockers until they are quiet. One at a time, loosen a rocker until it clatters. Then tighten the rocker slowly until it quiets down. This is zero valve lash.

OHC Engine Valves

There are several different methods of adjusting the valves on an overhead cam (OHC) engine. Many are adjusted like mechanical lifters in a pushrod engine. The rocker arm adjuster is turned until the correct size feeler gauge fits between the rocker or cam lobe and the valve stem.