Generac Power Systems OHVI GSH 190, Service Manual

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2-
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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.
SNAP
RING
CONNECTING
ROD
CONNECTING
ROD CAP
CONNECTING
ROD CAP BOLT
WRIST PIN
RINGS
PISTON
Figure 12-1. Pistons, Rings and Connecting Rod
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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:
. Remove the cylinder head (see Section 6).
2. Remove the crankcase cover (see Section )
. Remove the connecting rod cap bolts and the connecting
rod cap.
. Push the piston and rod out through top of cylinder.
PISToN
Figure 12-2. 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 is also provided to assist in
removing the wrist pin snap ring. To remove the piston from
the rod, proceed as follows:
. 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 2-).
NOTE: An assembly mark dimple is provided on top of
the piston. This mark must face the flywheel end of
crankshaft (3:00 position) during reassembly.
MAJOR DIAMETER
MINOR
DIAMETER
MEASURE AT A POINT
1.4-1.6 INCHES (35.5-40.5 mm)
FROM TOP OF PISTON
Figure 12-3. Piston Major and Minor Diameter
To check the piston for wear, proceed as follows:
. 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 .-.6 inches (5.5-
0.5mm) (see Figure 2-).
b. Measure at this point to check for wear. If wear is exces-
sive, replace the piston. See SPECIFICATIONS in Section
(Small Frame) or Section 5 (Large Frame) for proper
dimensions.
2. Check wrist pin for looseness.
a. A quick check for wear in (a) the wrist pin, (b) wrist pin
bore in piston or (c) wrist pin bore in rod is to check for
looseness or play with the piston assembled to the rod.
b. Looseness or play indicates a worn wrist pin, or a worn
wrist pin bore in the piston or rod.
SeCTIoN 12: PISToN, rINGS & CoNNeCTING rod INSPeCTIoN & ASSeMblY
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