Generac Power Systems GN190H, Service And Repair Manual

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SECTION 10: PISTON, RINGS AND ROD
38
GENER
A
C
GENERAL
There are no oversize pistons or rings available for these
engines. For that reason, if the cylinder is damaged or worn
excessively, the crankcase must be replaced.
Figure 10.1 — Pistons, Rings and Connecting Rod
REMOVAL
Before attempting to remove the piston and connecting rod,
clean all carbon from the cylinder bore (to prevent ring break-
age). Then, remove the piston and rod as follows:
1. Remove the cylinder head (see Section 9).
2. Remove the crankcase cover (see Section 11)
2. Remove the connecting rod cap bolts and the connecting
rod cap.
3. Push the piston and rod out through top of cylinder.
PISTON
Figure 10.2 — Piston , Wrist Pin and Snap Ring
REMOVAL FROM CONNECTING ROD:
An oil hole in the wrist pin area of the piston helps distribute
oil to aid in cooling. This oil hole also provides an assist in
removing the wrist pin snap ring. To remove the piston from
the rod, proceed as follows:
1. Move the snap ring around until its protruding wire is
aligned with the notched-out oil hole. Use needle nose pliers
to turn the snap ring and pull it toward you.
2. With one snap ring removed, slide the wrist pin out of its
piston boss. Completely remove the wrist pin and separate
the piston from the connecting rod.
CHECK PISTON FOR WEAR:
The piston is slightly elliptical. Its larger diameter is 90º from
the wrist pin boss; its smaller diameter is in line with the wrist
pin boss (see Figure 10.3).
NOTE: An assembly mark is provided on the piston This
mark must face the flywheel end of crankshaft (3:00
position) during reassembly.
Figure 10.3 — Piston Major and Minor Diameter
To check the piston for wear, proceed as follows:
1. Check the pistons MINOR DIAMETER.
a. At a position directly in-line with the wrist pin hole,
measure down from top of piston to a distance of 1.4-
1.6 inches (35.5-40.5mm) (see Figure 10.3).
b. Measure at this point to check for wear. If worn exces-
sively, replace piston.
2. Check the piston's MAJOR DIAMETER.
a. At a point 90º from the wrist pin hole, measure down
from top of piston to a distance of 1.4-1.6 inches (35.5-
40.5mm) (see Figure 10.3)
b. Measure at this point to check for wear. If wear is exces-
sive, replace the piston.
PISTON MINOR DIAMETER
GN-190, GN-191, GN-220
2.747-2.748 inches (69.789-69.809mm)
PISTON MAJOR DIAMETER
GN-190, GN-101, GN-220
2.753-2.754 inches (69.939-69.959mm)
3. Check wrist pin for looseness.
MAJOR DIAMETER
2.753-2.754 in
(69.939-69.959mm)
MEASURE AT A POINT
1.4-1.6 inches (35.5-40.5 mm)
FROM TOP OF PISTON
MINOR DIAMETER
2.747-2.748 in
(69.789-69.809mm)
SNAP
RING
CONNECTING
ROD CAP
CONNECTING
ROD
BOLT CAP
CONNECTING
ROD
WRIST
PIN
RINGS
PISTON