Generac Power Systems NP-40G - Manual (Page 47)

Section 2.3- PISTON, RINGS, CONNECTING ROD
Cylinder Service (Continued)
REBORING THE CYUNDER;
Always resize the cylinder bore to EXACTLY 0.010
Inch or 0.020 Inch (0.25 or 0.50mm) over the standard
cylinder dimensions. If this Is done accurately, the ser­
vice oversize ring and piston will fit and correct clear­
ances will be maintained.
STANDARD CYUNDER 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 andlubrlcatlon
recommended by the hone manufacturer to produce the
proper cylinder bore finish. Proceed as follows:
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 wail. 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
straightness. 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 (0.01mm) 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 thor­
oughly.
7. Replace the piston and rings with parts of correct
oversize.
Page 2.3-4