Cummins/Onan — Valve Clearance Adjustment, Two-Cylinder JB
Adjustments · Valve train
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
- Set valve clearance with engine at room temperature (approx 75 deg F); allow at least two hours cooling.
Procedure
- Turn flywheel until cylinder to be adjusted is on its compression stroke, after intake valve closes.
- Turn flywheel until TC mark lines up with timing pointer, then 10 to 45 degrees further clockwise.
- Check cylinder head bolt torque (28-30 ft-lb).
- Check clearance between rocker arm and valve with feeler gauge; adjust with locknut to Table 3 value.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Intake .012 in. Begin Spec D / .010 in. prior
- Exhaust .015 in. Begin Spec D / .013 in. prior
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.