Generac Power Systems 941-2, 940-2 Section PISTON, RINGS, CONNECTING ROD, Oversize Piston & Rings

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

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.

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.

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.

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