Cummins/Onan — Adjust Valve Clearance (Diesel)
Adjustments · valves
From a Cummins/Onan service manual covering: 12.0MDJC-3CR, 12.0MDJF-53CR, 15.0MDJF-18R, 15.0MDJF-3CR, 3.0MDJA, 3.0MDJA-3CR, 3omDJaiR, 4.0MCCK-3CR, 6.0MDJE-518R, 6.0MDJE-53CR, 6.5MCCK-3CR, 6.OMDJE-S18R…. Check it applies to your exact model before use.
Applies to: Cummins/Onan 12.0MDJF-53CR, Cummins/Onan 15.0MDJF-3CR, Cummins/Onan 3.0MDJA, Cummins/Onan 6.0MDJE-518R, Cummins/Onan 6.0MDJE-53CR, Cummins/Onan 6.5MCCK-3CR
Procedure
- Turn flywheel to compression stroke for cylinder to adjust.
- Turn flywheel clockwise additional 10 to 45 degrees.
- Loosen locknut to increase clearance, tighten to reduce.
- Use feeler gauge to set proper gap.
- Adjust in firing order 1-2-4-3.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- check at room temperature about 70°F (21°C)
Full service-parts list: Cummins/Onan 12.0MDJF-53CR →, Cummins/Onan 15.0MDJF-3CR →, Cummins/Onan 3.0MDJA →, Cummins/Onan 6.0MDJE-518R →, Cummins/Onan 6.0MDJE-53CR →, Cummins/Onan 6.5MCCK-3CR →
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.