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 an 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-402 engine".

Ремонт и замена масляного насоса ЗМЗ-402Ремонт и замена масляного насоса ЗМЗ-402

With a head or a 13 key, unscrew the two nuts securing the oil pump

We remove the oil pump

When the oil pump was removed due to a defect - (the oil pressure does not correspond to the norm), then you should immediately pay attention to the oil pump intake mesh.

It happens that the oil receiver mesh is very heavily clogged and therefore there is little oil pressure.

You can rinse the oil pump assembly, dip it into a container with gasoline, and rotate the drive gear, rinse the pump.

Dismantling the oil pump

Ремонт и замена масляного насоса ЗМЗ-402Ремонт и замена масляного насоса ЗМЗ-402

With a 12 key, unscrew the four screws securing the oil receiver

We remove the oil receiver of the oil pump

Ремонт и замена масляного насоса ЗМЗ-402Ремонт и замена масляного насоса ЗМЗ-402

Remove the cover

We take out the drive gear

Ремонт и замена масляного насоса ЗМЗ-402

We take out the driven gear

Ремонт и замена масляного насоса ЗМЗ-402

Undo the cotter pin of the pressure reducing valve and remove its parts

Inspection and fault detection of the oil pump

1. If the partition (cover for mod. 402) has a wear from the gears, it must be sanded so that there are no traces of wear.

2. Inspect the case. If it is badly worn, the pump must be replaced.

3. The gears in the pump housing must rotate completely free.

4. The plunger of the pressure reducing valve must move completely freely in the body.

5. Inspect the pressure relief valve spring. If cracks or broken coils are visible on it, replace the spring.

The length and stiffness of the spring have been selected at the factory so that the operation of the pressure reducing valve is optimal, therefore the length and stiffness of the spring must not be altered 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.

Осмотр и дефектация масляного насосаОсмотр и дефектация масляного насоса

The gap between the ends of the gears and the plane of the body should be 0.040-0.140 mm.

When measuring with a flat feeler, the gap between the outer diameter of the gears and the housing should be 0.120-0.215 mm

Осмотр и дефектация масляного насоса

The gap between the gear teeth should be no more than 0.15 mm

If these values do not correspond, then you need to replace the pump parts or replace the pump

Assembling the pump

We assemble the oil pump in 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.

Do not install a gasket of a different thickness or use sealant, paint, etc. when installing the gasket, as this will reduce the pump performance.

Install the pump in reverse order.

Tighten the oil pump mounting nuts with a torque of 18-25 Nm (1.8-2.5 kgf.m).