Dismantling
1. Remove the fixing screws and the back cover of the pump (photo).
Location of the oil pump cover bolts (arrows)
2. Remove all mechanisms from the pump housing. You may have to rotate the case to remove the mechanisms.
3. Place the pump body in a soft vice and remove the ferrule, plug, pressure regulator valve tappet and spring.
18 Oil pump components
1. Oil strainer; 2. gasket; 3. Bolt; 4. Pump cover; 5. External gear; 6. Internal gear; 7. Crimp ring; 8. Assembly of the plunger (switch stem); 9. Oil seal; 10. Pump housing
Inspection
4. Wash the oil pump parts in solvent.
5. Inspect components for wear, cracks, or other damage.
6. Check the external clearance (intermediate gear) pinion/crescent, pinion internal clearance (drive unit), crescent, gear/pump housing external clearance and gear/cover clearance, referring to the accompanying illustrations and Specifications.
Internal clearance check (A) and external (IN) pinion gear and crescent oil pump
Checking Gear/Oil Pump Cover Clearance | 
Checking clearance outer gear/oil pump housing |
7. Replace the seal along the way.
Assembly
8. Install valve, plug and spring assembly and ferrule.
9. Lubricate and install mechanisms.
10. Install the pump cover and tighten the screws securely. Use a thread binder.