Onan NHC Series Operator's/Service Manual And Parts Catalog page 183

Space each ring gap one third of the way around the
piston from the preceding one, with no gap directly
in line with, the piston pin. The bottom piston ring
groove should be fitted with an expander and an o i l
control ring and the two upper grooves fitted with
compression rings. I f a chrOme faced ring is used,
it w i l l be in the top groove. The o i l control ring is
selected for best performance in regard to the correct
unit pressure characteristics.
The piston is fitted with a full-floating type piston pin.
The pin is kept in place by two lock rings in the piston,
one at each side. Be sure these lock rings are properly
in place before installing the piston and connecting
rod in the engine. Refer to Dimensions and Clearances
for the correct piston-to-cylinder clearance.
CONNECTING RODS
The connecting rods should be serviced at the same
time the pistons or rods are serviced. Rods must be^.
removed with the piston. Replaceable bushings and
bearings are used. Bearings are available in standard
or .002", .010", .020 " o r .030 " undersize.
Proper clearance is obtained by replacing the pin
bushing and the bearings. The rod bearings are preci-
sion size and require no reaming.
Install the connecting rods and caps with raised lines
(witness marks) aligned and with the caps facing toward
the o i l base. The rod and cap numbered 2 f i t s on the
crankshaft journal nearest the bearing plate. Coat the
crankshaft journal bearing surfaces with o i l before
installing the rods. Crank the engine by hand to see
that the rods are free. If necessary, rap the connecting
rod cap screws sharply with a soft-faced hammer to set
the rod square on the journal.
again lubricate with o i l after installing (Figure 53).
Use combination bearing driver 420B324 to install the
camshaft bearings.
Replacement camshaft bearings are precision type
which do not require line reaming or line boring after
installation. Coat the bearing with lubricating o i l to
reduce friction. Place the bearing on the crankcase
over the bearing bore with the lubricating hole (front
only) in proper position. Be^sure to start the bearing,
straight. Press the front bearing in flush with the
outside erid of the bearing bore. Press the rear bearing
in until past the ignition plunger hole.
P R E C I S I O N T V P E - D O N O T L I N E R E A M O R B O R E .
W I T H H O L E - ^ V
I N B E A R I N G B O R E
O U T S I D E
FIGURE 53. CAMSHAFT BEARING
New crankshaft main bearings are precision type which
do not require line reaming or line boring after i n s t a l l a -
tion. They are available in standard size, .002", . 0 1 0 " ,
. 0 2 0 " or . 0 3 0 " undersize.
CRANKSHAFT
Inspect the bearing journals. If they are scored and
cannot be smoothed out by dressing down, the bearing
journals should be refinished to use nearest available
undersize bearings or a new crankshaft should be
installed. If a worn main bearing journal cannot be
fitted with an available precision type undersize
bearing, then refinish it to the next undersize. If a
worn rod journal cannot be fitted by installing new
bearing inserts (forged rod), then refinish it to take
the corresponding undersize bearing insert available.
Whenever making major repairs on the engine, always
inspect the drilled passages of the crankshaft. Clean
them to remove any foreign material and to assure
proper lubrication of the connecting rods.
BEARING^
w
Removal of «,i 'camshaft or crankshaft bearings requires
complete dist.:;sembly of the engine. Use a press or a
suitable drive plug to remove the bearings. Support the
casting to avoid distortion and avoid damaging the
bearing bore during removal and installation. Use o i l on
the bearings to reduce friction when installing and
Before putting in the main bearings, expand the bearing
bore by placing the casting in hot water or in an oven
heater to 2 0 0 0 F . If practical, cool the precision bear-
ing to shrink i t .
For putting in either the front or rear main bearing,
using instructions f o l l o w i n g , always align the o i l
hole(s) in the bearing with the o i l hole(s) in the bearing
bore. The o i l passage must be at least 1/2 open.
The cold oiled precision bearing should require
light taps to position i t .
only
NOTE: Engines shipped from the factory have separate
thrust washers and main bearings for both front and rear
of engine. Front bearing replacement part is a one
piece bearing (with attached thrust washer) as shown
in Figure 55. Do not add an additional thrust washer
to this front bearing. ,
In the rear bearing plate, i n s t a l l the bearing flush to
1 / 6 4 " below the end of the bore using combination
driver 420B324 (same one used for camshaft bearing).
See Figure 54.
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