Onan JB Service Manual

3.
4.
If ignition timing isn't correct, align 5"ATC mark
and timing pointer, then loosen breaker plate
capscrews and rotate plate
until light goes Out.
Clockwise rotation advances timing,
counterclockwise rotation retards
it (Figure 37)-
Tighten plate and check timing, step 2. If timing
isn't correct, readjust plate. If correct, connect
ignition lead and install cover.
FIGURE 37. JB-JC TIMING MARK
Timing Procedure, Engine Running:
Do not run the engine for more than a minute
or two with access dooropen or removed.The
engine overheats rapidly and can damage itself. Run without load.
1.
2.
3.
If
Remove access door and install an automotive
timing light on either of spark plug leads.
Run engine at rated speed and check timing with
light. If timing is incorrect, loosen breaker plate
mounting screw and correct it by rotating plate.
Rotating clockwise advances timing; turning
counterclockwise retards it. Tighten plate and
recheck timing point.
Adjust timing at
25'8TC (35" for Gas or Gas/
Gasoline), tighten breaker plate and then recheck
ignition point gap.
the breaker points can't be adjusted to
specifications, either the timing gear or camshaft gear
is incorrectly installed, or the centrifugal advance
mechanism is defective. Disassemble the breaker
mechanism for repair.
Breaker Points
The breaker points operate from a cam located on the
timing or start-disconnect gear. This gear is driven by
the camshaft gear.
Disassembly:
1. Disconnect battery to prevent accidental shorts.
2- Remove breaker point cover and disconnect
wires from start-disconnect switch (if used) and
ignition breaker points.
3. Remove two capscrews holding breaker plate
assembly and pull off plate.
4. Pull out cam and weight assembly. Be careful not
to lose spacer mounted on gear shaft.
5. To disassemble breaker plate assembly, remove
condenser and points and
pull out plunger and
pl unger d iap h rag m.
Repair: Thoroughly clean the gear and cam assembly.
The weights should move freely in and out without
catching in either end position. Inspect the gear ramp for
notches or other defects.
If any part of the cam weight and
gear assembly sticks, replace the complete assembly.
If
the cam is loose on the gear replace the complete
assembly. Clean and inspect the bearing surfaces in the
breaker plate and gear case. Clean the oil trickle holes
into these bearings. Check the oil spray hole in the gear
case to be sure it is open. If the breaker points won't
maintain the proper gap, check for excess wear in both
the cam and the ignition breaker plunger.
.
Assembly:
1. Install springs on weight assemblies. Install cam
on gear shaft, being sure to align timing marks
(Figure
39), and install cam spring. Weights
should snaooutward between lOOOand
1075 rpm.
2.
3.
4.
5.
6.
If necessary, adjust by lightly bending one or both
spring anchor pins toward center of gear.
Install spacer and thrust washer on gear shaft
assembly and install assembly into gearcase,
matching timing marks on timing gear and
camshaft gear.
Install spring and plunger
on end of shaft.
Install breaker plate. Install ignition plunger and
diaphragm and diagram cup (Figure
40).
Install start-disconnect diaphragm (when used),
and plunger, and install start-disconnect breaker
points.
Adjust start-disconnect breaker point gap to
.020
inch.
31
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Onan JB Specifications

General

Brand	Onan
Model	JB
Category	Engine
Language	English