The oil pump is removed, repaired or replaced during a major overhaul of the engine or when the pressure in the lubrication system decreases
Drain the oil from the crankcase.
Remove the oil pan.
On the engine mod. 402 unscrew the two nuts 1 and remove the pump 2 with the receiver as an assembly.
On the engine mod. 406 unscrew the three bolts and remove the pump with the receiver assembly.
Oil pumps for engines mod. 402 and 406 are similar in design.
1. Pull out the hexagonal shaft of the oil pump drive.
2. Remove the mesh from the receiver by folding the edges of the mesh.
3. Unscrew four bolts 3 and remove the receiver 2 and partition 1.
4. Remove drive gear 1 with shaft and driven gear 2.
If you need to remove the drive gear from the roller, knock out the pin
5. Remove cotter pin 1, washer 2, spring and pressure reducing valve plunger installed under washer 2.
6. Rinse the pump parts with gasoline and blow with compressed air.
Inspection and repair
If there is wear on the partition (cover for mod. 402), it must be sanded so that no traces of wear remain.
Inspect the hull. If it is badly worn, you need to replace the pump.
The gears in the pump housing must turn completely freely.
The pressure relief valve plunger must move completely freely in the body.
Inspect 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.
The length of the spring in the free state must be 50 mm, the force to compress the spring by 10 mm must be 46 N (4.6 kgf) for the engine mod. 406.
For engine mod. 402, 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 pump is assembled in the reverse order.
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 the reverse order of removal.