Onan NHC Series Operator's/Service Manual And Parts Catalog page 186

CYLINDER HEADS
Remove the cylinder heads for cleaning at least every
400 hours or when poor engine performance is noticed.
1. Use a 1/2 inch socket wrench to remove cylinder
head bolts. L i f t heads off.
CAUTION
Do not remove heads when they
^y^y^J, are hot. Warpage may occur.
2. After removing heads, clean out a l l carbon de-
posits. Be careful not to damage the outer sealing
edges where gaskets f i t . The heads are made of
aluminum and can be damaged by careless handling.
3. Use new head gaskets and clean both the heads
and the cylinder block thoroughly where the head
gaskets rest.
4. Place heads in position and follow head torque
tightening sequence shown in Figure 59. Start out
• tightening a l l bolts to 5 f t - l b , then 10 f t - l b , etc.,
u n t i l a l l bolts are torqued to 17-19 f t - l b .
5. Recheck torque before engine has run a total
of 50 hours.
8
=®=m>=.
m
LEFT C Y L I N D E R
RIGHT C Y L I N D E R
FIGURE 59. HEAD BOLT TIGHTENING SEQUENCE
38