Generac Power Systems 04389-1, 04456-1, 04390-1 Adjusting GH-410/GT-990 Valve Clearance

Lead-acid batteries present a risk of fire because they generate hydrogen gas. The following procedures are to be followed:

•DO NOT SMOKE when near the battery;

•DO NOT cause flame or spark in battery area; and

•Discharge static electricity from your body before touching the battery by first touching a grounded metal surface.

Be sure the Auto/Off/Manual switch is set to ! the OFF position before connecting the battery

cables. If the switch is set to AUTO or MANUAL, the generator can crank and start as soon as the battery cables are connected.

Be sure the utility power supply is turned off and the 5A and 15A fuses are removed from the generator control panel, or sparking may occur at the battery posts as the cables are attached and cause an explosion.

4.8ADJUSTING GH-410/GT-990 VALVE

CLEARANCE

After the first 50 hours of operation, adjust the valve clearance in the engine.

Important: If feeling uncomfortable about doing this procedure or the proper tools are not available, please contact the Generac Authorized dealer for service assistance. This is a very important step to insure longest life for the engine.

To adjust valve clearance:

•Make sure the engine is at room temperature.

•Make sure that the spark plug wire is removed from the spark plug and out of the way.

•Remove the four screws attaching the valve cover with a #2 or #3 phillips screwdriver.

•Make sure the piston is at Top Dead Center (TDC) of its compression stroke (both valves closed). To get the piston at TDC, remove the intake screen at the front of the engine to gain access to the flywheel nut. Use a large socket and socket wrench to rotate the nut and hence the engine. While watching the piston through the spark plug hole. The piston should move up and down. The piston is at TDC when it is up as high as it can go.

•Loosen the rocker jam nut. Use an 10mm allen wrench to turn the pivot ball stud while checking clearance between the rocker arm and the valve stem with a feeler gauge. Correct clearance is 0.002-0.004 inch (0.05-0.1 mm).

NOTE:

Hold the rocker arm jam nut in place as you turn the pivot ball stud.

When valve clearance is correct, hold the pivot ball stud in place with the allen wrench and tighten the rocker arm jam nut. Tighten the jam nut to 174 in/lbs. torque. After tightening the jam nut, recheck valve clearance to make sure it did not change.

Figure 4.10 - Valve Clearance Adjustment

Rocker

Pivot BallArm

Stud

Jam Nut

Valve

Stem

•Install new valve cover gasket.

•Re-attach the valve cover. NOTE:

Start all four screws before tightening or you will not be able to get all the screws in place. Make sure the valve cover gasket is in place.

•Re-attach the spark plug wire to the spark plug.

•On GT-990, Repeat the process for the other cylinder.

4.9COOLING SYSTEM

Air inlet and outlet openings in the generator com- partment must be open and unobstructed for contin- ued proper operation. This includes such obstruc- tions as high grass, weeds, brush, leaves and snow.

Without sufficient cooling and ventilating air flow, the engine/generator quickly overheats, which causes it to quickly shut down. (See Figure 4.9 for vent loca- tions.)

Figure 4.9 – Cooling Vent Locations