Generac Power Systems 941-2 - Manual (Page 47)

Section 2.3
PISTON, RINGS, CONNECTING ROD
OVERSIZE PISTON & RINGS
Worn or scored cylinders may be rebored to 0.010
(0.25mm) or 0.020 (0.50mm) oversize. Pistons and
piston rings of matching oversize are available to fit
the rebored cylinder.
Figure 1. Piston, Rings and Connecting Rod
PRIOR TO REMOVAL
Before removing pistons, rings and connecting rod,
clean all carbon from the cylinder bore. Carbon
buildup in the cylinder bore can cause ring breakage
during piston removal.
REMOVAL
Remove the connecting rod CAP BOLTS and the
connecting rod CAP. Then, push the piston and con-
necting rod out through top of cylinder.
PISTON
REMOVE FROM CONNECTING ROD:
NOTE: An oil hole in the wrist pin area of the pis-
ton helps distribute oil to assist in cooling. The oil
hole also provides an assist In removing the wrist
pin snap ring.
To remove the piston from the connecting rod, pro-
ceed as follows:
1. Move the snap ring around until Its protruding end 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 the pis-
ton boss. This will separate the piston from the connecting rod.
F figure 2. Piston Pin Removal
CHECK FOR PISTON WEAR:
The piston is slightly elliptical. It's smaller diameter is
in line with the wrist pin boss. It's larger diameter is
90° from the wrist pin boss.
NOTE: An assembly mark Is provided on the pis-
ton. This mark should face the flywheel end of the
crankshaft (3:00 position) during reassembly.
Figure 3. Elliptical Shape of Piston
To check the piston for wear, proceed as follows:
1. Minor Diameter: At a position directly in line with the wrist pin
hole, measure from top of piston down to a distance of 1.4-1.6
inches (35.5-40.5mm). This is the "minor" diameter. Measure at
this point to check for wear.
2. Major Diameter: At a point 90° from the wrist pin bore, measure
down 1.4-1.6 inches (35.5-40.5mm). This is the "major" diame-
ter. Measure at this point to check for piston wear. Replace the
piston if wear limits are exceeded.
3. Check wrist Pin for Looseness: A rough check for wear in the
wrist pin, wrist pin bore in the piston, or wrist pin bore in the
connecting rod is to check for looseness or play with the piston
assembled to the rod. Looseness or play indicates a worn wrist
pin, or a worn bore in the piston or connecting rod.
Page 2.3-1