Generac Power Systems 940-2, 941-2 service manual Cylinder Service, Match Marks on Rod and Cap

Section 2.3

PISTON, RINGS, CONNECTING ROD

hammer handle to gently tap the piston down into the cylinder.

4.Check that the connecting rod's large diameter bearing is coat- ed with oil, as well as the crank throw and the connecting rod cap.

5.Guide the large end of the connecting rod onto the crankshaft. Install the connecting rod cap. The match mark on the cap must be aligned with an identical mark on the rod (Figure 10).

6.Install the connecting rod cap bolts and tighten to the proper torque.

TIGHTENING TORQUE

CONNECTING ROD CAP BOLTS (GV-220)

10 foot-pounds (1.36 N-m)

NOTE: The connecting rod can be installed in either direction. That is, the cap marks on the rod and cap may face toward the installer or away from the installer. The only requirement is that the assembly mark on top of piston be toward the fly- wheel side of engine.

Figure 10. Match Marks on Rod and Cap

CYLINDER SERVICE

INSPECTION:

Check the cylinder for dirty, broken or cracked fins. Also look for worn or scored bearings, or a scored cylinder wall. Check the cylinder head mounting sur- face for warpage. If the head is warped, it must be replaced. If the cylinder bore is worn (as evidenced by excessive ring end gap), the cylinder should be replaced or rebored to 0.010 or 0.020 (0.25 or 0.50mm) oversize.

After reboring the cylinder to a specific oversize, install an identically oversize piston along with identi- cally oversized rings.

Always resize the cylinder bore to EXACTLY 0.010 inch or 0.020 inch (0.25 or 0.50mm) over the stan- dard cylinder dimensions. If this Is done accurately, the service oversize ring and piston will fit and correct clearances will be maintained.

STANDARD CYLINDER BORE DIAMETER

MINIMUM: 2.7560 inches (70.000mm)

MAXIMUM: 2.7570 Inches (70.025mm)

To rebore the cylinder, use a commercial hone of suitable size chucked In a drill press having a spindle speed of about 600 rpm. Use the stones and lubrica- tion recommended by the hone manufacturer to pro- duce the proper cylinder bore finish. Proceed as fol- lows:

1.Start with coarse stones. Center the cylinder under the drill press spindle. Lower the hone so that the lowest end of the stone contacts the lowest point in the cylinder bore.

2.Begin honing at bottom of cylinder. Move the hone up or down at about 50 strokes per minute, to avoid cutting ridges In the cylinder wall. Every fourth or fifth stroke, move the hone far enough to extend it one (1) Inch beyond the top and bottom of the cylinder bore.

3.Every 30 or 40 strokes, check the bore for size and straight- ness. If stones collect metal, clean them with a wire brush.

4.Hone with coarse stones until the cylinder bore is within 0.002 inch (0.05mm) of the desired finish size. Then, replace the coarse stones with burnishing stones and continue until bore is within 0.0005 inch (0.01 mm) of the desired size.

5.Install finishing stones and polish the cylinder to its final size.

6.Clean the cylinder with soap and water. Dry thoroughly.

7.Replace the piston and rings with parts of correct oversize.

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