Generac Power Systems OHVI GSH 220 Service Manual page 50

SeCTIoN 12: PISToN, rINGS & CoNNeCTING rod INSPeCTIoN & ASSeMblY
NOTE: Tolerances between the wrist pin and wrist pin
bores are extremely close. Always apply engine oil to
the pin and its bores prior to installation.
. Check wrist pin and wrist pin bores for wear.
a. Measure the outside diameter of the wrist pin.
b. Measure the inside diameter of the wrist pin bore in
piston.
c. Measure the inside diameter of the wrist pin bore in con-
necting rod.
d. Measure the wrist pin length.
. If excessive wear is found, replace the worn part. See
SPECIFICATIONS in Section  (Small Frame) or Section
5 (Large Frame) for proper dimensions.
PISToN rINGS
GENERAL:
The following general rules pertaining to piston rings must
always be complied with:
• Always replace piston rings in sets.
• Use a ring expander to remove or install piston rings, or
breakage could result. Do not spread the rings too far apart
or they might break.
• Use a ring compressor when installing the piston into the
cylinder.
• When installing NEW rings, deglaze the cylinder walls with
a commercially available deglazing tool.
PISTON (CUTAWAY VIEW)
Figure 12-4. Location of Rings in Piston Grooves
TOP COMPRESSION RING
EITHER SIDE UP
2ND COMPRESSION RING
CHAMFER FACING UP
OIL CONTROL RING
EITHER SIDE UP
2-2
DESCRIPTION:
A piston ring set consists of (a) a top compression ring, (b) a
second compression ring and (c) an oil ring assembly.
• The OIL CONTROL RING is a three-piece assembly consisting
of two oil rails and an oil spacer ring. Oil rails have a rounded
face and may be installed with either side up.
• The second compression ring has an inside chamfer. This
chamfer must face upward when installing the ring.
• The top compression ring has a barrel shaped face and can
be installed with either side facing up.
RING END GAP:
Inside the cylinder, locate a point that is 2.75 inches (70mm)
down from the top of the cylinder (about halfway down). Place
ring into cylinder and use the piston to push the ring down
to the stated depth. Check ring end gap with a feeler gauge.
See Figure 2-5.
If the end gap of a new ring is excessive, the cylinder is worn
excessively. See SPECIFICATIONS in Section  (Small Frame) or
Section 5 (Large Frame) for proper dimensions.
NOTE: Oversize pistons and rings are not available. If
the cylinder is worn or damaged, the crankcase must
be replaced.
Figure 12-5. Measuring Ring End Gap
CoNNeCTING rod
The connecting rod is manufactured of die-cast aluminum.
Match marks on the rod and on the rod cap must be aligned
when assembling the rod to the crankshaft. See Figure 2-6.
*
CAuTIoN! do NoT uSe A wASHer wHeN ASSeM-
blING THe rod CAP.