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20 Generac
®
Power Systems, Inc.
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 body before touch-
ing 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.
4.8 ADJUSTING 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 the pivot
ball stud is turned.
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
• Install new valve cover gasket.
• Re-attach the valve cover.
NOTE:
Start all four screws before tightening or it will not
be possible 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.
4.9 COOLING 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
Jam Nut
Pivot Ball
Stud
Rocker
Arm
Valve
Stem
!
Section 4 — Maintenance
Guardian Air-cooled 7 kW, 12 kW and 15 kW Generators