Cummins/Onan — Oil Pump Removal and Repair
Repair & overhaul
From a Cummins/Onan service manual covering: 10.0JC, 12.5JC, 15.0JC, 4.0JB, 5.0JB, 6.0JB, 6.1JB, 7.5JB, 7.6JB. Check it applies to your exact model before use.
Applies to: Cummins/Onan 10.0JC, Cummins/Onan 12.5JC, Cummins/Onan 15.0JC, Cummins/Onan 5.0JB, Cummins/Onan 6.0JB, Cummins/Onan JB engine, Cummins/Onan JC engine
Before you start
- Component parts other than gaskets are not individually available; replace pump if worn.
Procedure
- Remove gear cover and oil base; unscrew intake cup from pump.
- Remove crankshaft lock ring and gear retaining washer.
- Loosen two capscrews holding the pump and remove the pump.
- Disassemble by removing two capscrews holding pump cover; inspect for excessive wear in gears and shafts.
- Adjust gear end clearance using thinnest gasket that permits free movement of pump shaft.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- .005 in. lash between pump gear and crankshaft gear
Full service-parts list: Cummins/Onan 10.0JC →, Cummins/Onan 12.5JC →, Cummins/Onan 15.0JC →, Cummins/Onan 5.0JB →, Cummins/Onan 6.0JB →
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.