Yanmar 4LHA-HTP Operation Manual page 463

Chapter 3 Fuel Injection Equipment
6. Fuel Feed Pump
Automatic pressure control mechanism
As the delivery
the pressure at t h e back of the piston also rises, over-
coming the p i s t o n spring force, and hindering the
lowering of the P iston. Thus, the fuel flow automatical-
ly stops, and t h e fuel pressure is maintained within
a fixed range.
Outle
Inside chamber
Outside c h a m b e r
( (
6-2 Fuel Feed Pump Disassembly
Follow the procedure below to disassemble the fuel
feed pump.
(1) Remove the piston spring stopper plug, and pull
out the piston and piston spring.
(2) Remove the snap ring, and pull out the tappet
assembly.
(3) Pull out the inter-spindle.
(4) Remove the priming pump.
(5) Remove the discharge valve spring stopper, and
remove the valve and spring from inside.
(6) Remove the O-ring.
6-3 Fuel Feed Pump Inspection
(1) Block the priming pump with your finger and
check whether the pressed-in piston returns by
spring force. If the piston returns, the piston does
not have enough negative pressure. Always replace
the priming pump as a set.
(2) Check the piston spring for cuts, cracks, uneven
wear and rust.
(3) If the piston, inter-spindle, or tappet assembly are
extremely worn, replace the part.
(4) Check the contact surface of the valve and valve
seat for defects.
(5) When there is play in a valve seat which has been
calked into the feed pump body, the whole fuel
pump body must be replaced.
V '
pressure of the fuel pump climbs,
Inlet
Inside chamber
J
Outside chamber
Inlet
I
Inside chamber
Outside chamber
1
Outlet
When the outside chamber pressure
overcomes the piston spring force,
the p i s t o n is pushed up a n d separated
f r o m the push rod.
NOTE: Play in the valve seat hinders the opening and
closing of the valve, causing insufficient
supply and abnormal
camshaft.
6-4 Fuel Feed Pump Reassembly
(1) To reassemble the fuel feed pump, follow the as-
sembly procedure in reverse order.
(2) When the pump has been reassembled, perform
the air-tightness test.
Apply 0.29(3)MPa(kgf/cnn) of air pressure to the
discharge outlet of the pump, a n d check for air
leaks from the O-ring. If air is leaking, replace the
O-ring.
Measuring cylinder
Tappet - -c^z^LJ
Blocked
3-2-41
4LHA Series
A t r a t e d pressure rise
fuel
wear of the tappets and
Air pressure MPa (kgf/cm
-~" z:
Container filled
with diesel fuel
)
1