The engine oil pump is a conventional gear pump.
The principle of operation of the pump: when the gears rotate, a vacuum is created on the inlet side, as a result of which the liquid fills the cavities between the teeth and moves in them from the inlet side to the outlet side.
We remove the oil pump if the oil pressure does not correspond to the norm and during the overhaul of the engine.
To remove the oil pump, you need to remove the oil pan, as described in the article - "How to disassemble the ZMZ engine -402".
Using a 13 socket or wrench, unscrew the two nuts securing the oil pump
Remove the oil pump
When the oil pump was removed due to a defect - (the oil pressure is not up to standard), then you should immediately pay attention to the grid of the oil pump intake.
It happens that the oil receiver mesh is very clogged and therefore the oil pressure is low.
To flush the oil pump, you can dip the assembly into a container of gasoline, and rotate the drive gear to flush the pump.
Oil pump disassembly
Using a 12 key, we unscrew the four screws securing the oil receiver
Remove the oil receiver of the oil pump
Remove the cover
Removing the drive gear
Take out the driven gear
We unpin the fastening of the pressure reducing valve and remove its parts
Oil pump inspection and troubleshooting
- 1. If there is wear from gears on the partition (cover for mod. 402), it must be sanded so that no traces of wear remain.
- 2. Examine the hull. If it is badly worn, the pump needs to be replaced.
- 3. The gears in the pump housing must be completely free to rotate.
- 4. The pressure reducing valve plunger must move completely freely in the body.
- 5. Check the relief valve spring. If cracks are noticeable on it or the coils are broken, replace the spring.
The length and stiffness of the spring are selected at the factory in such a way that the operation of the pressure reducing valve is optimal, therefore, the length and stiffness of the spring must not be changed in any way.
For the ZMZ-402 engine, in order to compress the spring to a length of 40 mm, it is necessary to apply a force of 43.5–48.5 N (4.35–4.85 kgf).
If the spring does not meet at least one of these requirements, it must be replaced.
The gap between the ends of the gears and the plane of the housing should be 0.040-0.140 mm.
When measuring with a flat feeler gauge, the clearance between the outer diameter of the gears and the housing should be 0.120-0.215 mm
The gap between the gear teeth should be no more than 0.15 mm
If these values do not match, then you need to replace the pump parts or replace the pump
Pump Assembly
We assemble the oil pump in the reverse order, lubricating the rubbing parts with engine oil.
When assembling the motor pump mod. 402 under the pump cover, you need to put a cardboard gasket 0.3 mm thick.
It is forbidden to install a gasket of a different thickness or use sealant, paint, etc. when installing the gasket, as this will reduce the performance of the pump.
Install the pump in reverse order.
We tighten the oil pump mounting nuts with a torque of 18-25 Nm (1.8-2.5 kgf.m).
