GMC 1976 ZEO 6083 Maintenance Manual page 697

24C- 2 0 ONAN MOTOR GENERATOR
Figure 26-Piston Rings
to prevent twisting or excessive expansion of the
ring . Some oil control rings and all compression
rings have a dot or the word "top" on one side of the
ring to indicate which side faces the top of the piston .
Unmarked piston rings can be installed either way.
If the oil control ring has a coil expander, install the
expander first and then close until the coil ends butt .
The joint should be 180° from the gap of that ring .
INSTALLATION OF PISTON IN
CYLINDER :
1 . Turn the crankshaft to position the number
one rod bearing journal at the bottom of its stroke.
2. Lubricate the number one piston assembly and
inside of the cylinder . Compress the rings with a ring
compressor as shown in Figure 27 .
3. Position the piston and rod assembly in the
cylinder block.
NOTE :
The connecting rod numbers should al-
ways face away from the camshaft or bottom
side of engine . See Figure 28 .
4. Tap the piston down into the bore with the
handle end of a hammer until the connecting rod is
seated on the journal (figure 27). Install the bearing
cap on the rod with the witness marks and stamped
reference numbers matching the marks on the rod.
Install and tighten the bolts to the specified torques.
The bearing cap must be tapped several times to
properly align it with the rest of the connecting rod.
Clearance varies on the journal if this is not done.
Install the remaining pistons and rods in the
same manner. Crank the engine over by hand to see
that all bearings are free .
Install oil pan.
Figure 27-Installing Piston
5 . Install the oil base with a new gasket .
Torque oil base thru-bolts to 18-23 ft .-lb.
6. Install the cylinder heads and torque 14-16 ft .
lb . (17-19 ft . lb. on 6KW) .
7 . Replace oil and break-in engine .
CYLINDER HEADS
Remove the cylinder heads for cleaning when
poor engine performance is noticed.
Figure 28-Piston Assembly
1 . Use a 1/2 inch socket wrench to remove cylin-
der head nuts . Lift heads off.