Cummins/Onan — Adjust valve clearance (two-cylinder)
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 6.1JB, Cummins/Onan 7.5JB, Cummins/Onan 7.6JB, Cummins/Onan JB engine, Cummins/Onan JC engine
Before you start
- Set clearances at room temperature, at least two hours after shutdown
Procedure
- Turn flywheel to compression stroke after intake valve closes
- Align TC mark with timing pointer, then turn clockwise 10 to 45 degrees
- Check cylinder head bolt torque
- Check rocker-arm-to-valve clearance with feeler gauge
- Adjust with locknut to Table 3 clearance
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- .012 in intake (Begin Spec D)
- .015 in exhaust (Begin Spec D)
Full service-parts list: Cummins/Onan 10.0JC →, Cummins/Onan 12.5JC →, Cummins/Onan 15.0JC →, Cummins/Onan 5.0JB →, Cummins/Onan 6.0JB →, Cummins/Onan 6.1JB →, Cummins/Onan 7.5JB →, Cummins/Onan 7.6JB →
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.