Cummins/Onan — Adjust valve clearance - Four-Cylinder J-Series engines
Adjustments · Valve train / rocker arms
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
- Early model four-cylinder engines do not have a BC mark on the flywheel
Procedure
- Adjust valve clearance in firing order (1-2-4-3) sequence
- Set timing for number 1 cylinder and adjust the valve clearance
- Turn flywheel clockwise 180 degrees for number 2 cylinder (between 10 and 45 degrees past BC mark)
- Adjust valve clearance for number 2 cylinder
- Turn flywheel clockwise 180 degrees for number 4 cylinder (between 10 and 45 degrees past TC mark)
- Adjust valve clearance for number 4 cylinder
- Turn flywheel clockwise 180 degrees for number 3 cylinder (between 10 and 45 degrees past BC mark)
- Adjust valve clearance for number 3 cylinder
Tools required
- feeler gauge Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Firing order 1-2-4-3
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.