Onan MDJA User Manual

The port closing (PC) mark is not stamped on replacement fly-
wheels.Therefore, the PC markmust beestablished by measuring
the piston drop with the cylinder head removed prior
to injection
pump timing. Since injection occurs at the port closing position,
the PC mark can be located only by comparing the old flywheel
with the new one, or
by measuring the piston drop from its top
center position on the compression stroke
of number one cylinder.
Piston drop data
is given in Table 7.
PISTON DROP
Inches I mm
TABLE 7. PISTON DROP DATA
.
PORT
BTC
ENGINE CLOSING
0.155
0.102 I 2.59
I MDJA I 17degrees
0.128 I 3.25
I MDJB & MDJC I 19 degrees
-
(Begin Spec P)
(Prior to Soec P)
3.94 MDJB & MDJC 21 degrees
0.128
0.115
0.128
3.25 MDJE Spec A-AA
19 degrees
2.9 MDJE Begin Spec AB
18 degrees
3.25 MDJF 19 dearees
CAUT,ON
Replace any injection pump that
Ez3 troubleshooting procedures prove
to be malfunctioning.
Do not attempt unauthorized
repair procedures
on the injection pumps.
Fuel injection pumps must pass stringent quality
inspections, and tests with precise settings and
adjustments, in order to meet Onan’s performance
and reliability requirements. Therefore,
it must be
clearly understood by the owners and by Onan ser-
vice personnel that tampering or inept repair attempts
can cause irrepairable damage to the pumps that will
not be covered by
the manufacturers’ warranties or
exchange agreements. Contact an authorized Amer-
ican Bosch Service station or Distributor for expert
repair service on injection pumps.
The Repair service should include cleaning, part
replacement, static pressure tests for internal and
external leaks, internal pump timing, and calibration
and adjustment to the manufacturer’s specifications.
MDJA INJECTION PUMP
INJECTION LINE
CAP NUT
VALVE HOLDER
SPRING
BLEED
VALVE ASSEMBLY
PUMP HOUSlN GASKET
GASKET
LOCATING SCREW
PLUNGER BARREL
CONTROL SLEEVE
CLOSING PLUG
UPPER SPRING SEAT
PLUNGER SPRING
PLUNGER RETAINING
RING
LOWER SPRING SEAT
A PLB injection pump (Figure 37) is used on the
MDJA Series e’ngines. The cross-sectional view
shows the internal parts and the operating lever and
control shaft.
The pump consists of a housing, pump plunger and
barrel, the plunger return spring with its seats, and
the control sleeve and its operting shaft. The housing
contains the fuel sump, delivery valve assembly,
delivery valve holder, and the union nut for connec-
tion
of the high pressure discharge tubing.
Repair
Most fuel system troubles are not due to a faulty
injection pump.Test the rest of
the fuel system before
condemning the injection pump.
Onan discourages field repair of the injection pump
because of the exceptionally close tolerances be-
tween parts and the specialized equipment necessary
for repair. The injection pump is an expensive part
of
the unit and even a particle of dirt as fine as talcum
powder could score its working surfaces. If the rest of
the fuel system is in working order and fuel delivery is
abnormal, remove the pump for replacement
or
repair.
Removal
Remove the pump inlet and outlet lines. Remove the
two capscrews holding the pump to the engine and
lift
it off. Do not lose the shims. They time the injec-
tion pump to the engine. Cap all openings in the
pump and fuel lines to keep dirt out of the fuel system.
Timing
Timing the pump to the engine determines the port
closing point
(17 degrees BTC) PC mark on flywheel.
See Figure
38. The helix position controls port open-
ing and is, in turn, controlled by the throttle setting.
FIGURE 37. PLB INJECTION PUMP COMPONENTS FIGURE 38. INJECTION PUMP TIMING
42
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Onan MDJA Specifications

General

Brand	Onan
Model	MDJA
Category	Engine
Language	English