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Maintain and Repair Diesel Generator Oil Pump

Sep. 20, 2018

The oil delivery pump of diesel generator set is single acting piston type. It is mounted o n the side of the fuel injection pump of the diesel generator set and is driven by an eccentric wheel on the injection pump shaft. Its function is to inhale fuel from the tank and supply enough fuel to the diesel generator injection pump with a certain pressure. Before starting the diesel generator set, pump the oil with the hand pump on the oil pump and remove the air from the oil circuit. It can smoothly absorb the fuel within 1 m below the center of the pump in 0.5min. The handle nut must be fastened after the pump oil. The technical specifications of the diesel generator pump are shown in figure 1.

Maintain and Repair Diesel Generator Oil Pump.jpg




Structure of Oil Pump

Fuel Injection Pump

Rated Condition



Oil pressure

kPa (kgf/cm²)

Fuel delivery


SB 2221

Roller type

4, 6 cylinders B series injection pump




SB 2214

SB 2215

Roller type

12 cylinder B series injection pump






The 4 and 6 cylinder B series and B series enhanced fuel injection pumps use roller pumps, as shown in figure 2a. The 12-cylinder B series fuel injection pump is equipped with two rolling wheels, the oil pump on the left and right sides of the inlet and outlet oil pipe joint and a hand pump mounted separately on the front end of the diesel engine block, as shown in figure 2b/c/d.






The matching clearance between the piston and the housing of the oil pump is 0.005-0.02 mm. If the gap is too large, the fuel supply rate will decrease. The jacking rod and the jacking sleeve of the rolling wheel oil pump are also paired and the gap is too large and there are also the disadvantages of oil leakage. Hand pump piston and hand pump body between the rubber sealing device, unless the rubber ring in the hand pump damage, generally should not be removed. The 12 cylinder V diesel generator has no rubber seal for the hand pump. It is sealed by matching clearance (not greater than 0.02mm).


The working principle of the oil pump is shown in figure 3. when the roller and the ejector rod of the oil pump are in the lowest position of the eccentric wheel of the fuel injection pump, the fuel in the upper chamber of the piston is squeezed out because the piston is driven upward by the action of the spring. Then the one-way valve on the oil outlet side closes and the fuel is sent to the fuel filter, and a space is formed in the lower chamber of the piston. The one-way valve on the oil inlet side is opened to absorb the fuel, as shown in figure 3a. the cycle is constant, the fuel is inhaled and discharged. When the oil pipeline resistance is increased to the same oil pressure at both ends of the piston, the piston is no longer in balance with the rod movement, and the oil pump stops working. As shown in figure 3 c.



Fig. 3a. The fuel oil enters the lower piston chamber, and the upper piston cavity discharges oil.


Fig. 3b. The fuel oil enters the upper cavity of the piston, and the lower chamber of the piston discharges oil.


Fig. 3c. The oil pressure of the upper and lower cavities of the piston is equal, the piston is in the balance position, and the upper and lower cavities do not drain oil.


Oil pump maintenance


Oil pump is an important component in diesel generator to support combustion power generation. Once failure occurs, it will lead to problems such as coke deposition, insufficient combustion, blocking and so on. So it reminds genset users to pay attention to the maintenance of oil pump is also an important task.


1. Before installing the oil pump, check whether the type and specifications are correct. The thickness of the gasket should be suitable to prevent the piston from dying or running out of place because it is too thin or too thick. Tighten the bolt when the toque to be uniform, to prevent damage to the oil pump.


2. There is rubber seal between the piston and the body of the hand oil pump in the oil pump. Do not remove it at will. The rubber ring should be replaced in time if it is damaged.


3. The coarse screen core in the connection of oil pump is easy to be clogged by dirt such as cotton flor, so it must be checked and cleaned


4. The hand oil pump must be pressed back to tighten the button to prevent air intake or oil leakage caused by the pressure off the pump and rubber ring or between the ball valve and the valve seat.


The parts should be inspected after long time use of the pump of the diesel generator set. The points for attention are as follows.


1. If the plane of the one-way valve is worn, sunken and pockmarked, the grinding paste shall be used to grind on the flat plate. As the following figure, serious should be replaced.

2. The surface of the one-way seat on the shell should be replaced when worn seriously or unevenly.

3. The wear between the top rod and the top rod sleeve is so serious that the clearance increases, the seal becomes worse and the diesel oil leak is too serious, it must be replaced together with the shell. Optionally increase the size of the rod, but with the shell replacement, or with the size of the rod, subject to mutual research.

4. The coarse filter core in the oil inlet joint is easy to be blocked by cotton wadding, which affects the oil supply. Therefore, it is necessary to pay attention to the cleaning of fuel and the removal of dirt on the filter core.

5. When the rubber ring of the piston pump is damaged, it should be replaced in time. The leakage of the piston of the hand pump used in the 12 cylinder V diesel generator set indicates that the matching surface is worn and the clearance is enlarged, which needs to be rescheduled.


Generator parts such as piston for oil conveyance in diesel generator set after reassembly. In the whole process should be good activity, no block and stuck phenomenon, pressure pump should be light and flexible. The one-way valve spring must be accurately embedded in the spring slot when installing the one-way valve spring.


Analysis and treatment method if common faults of oil transmission pump of diesel generator set.


Many diesel generators ignore the maintenance of oil pump in operation. In fact, oil pump is an important part of generator. Once the fault occurs, the diesel oil circulation in the low pressure oil circuit will be affected, thus affecting the normal operation of the diesel generator set.




Elimination Method

insufficient oil delivery


check valve wear or break


repair or replace


Piston wear

replace the piston

oil pipe joint oil leakage


tighten or repair again


filter blocking at oil inlet joint


clean filter

jacking rod oil spill


overhauling ejector rod


piston dead cut oil


remove and repair


hand pump leak

disassembly maintenance theory



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