Cummins/Onan B48 — Valve Clearance Adjustment
Adjustments · Valve System
For the Cummins/Onan B48, from the Cummins/Onan service manual.
Applies to: Cummins/Onan B48, Cummins/Onan B48M engine
Before you start
- Do not adjust when engine is warm
Procedure
- Remove ignition key to prevent accidental starting
- Remove all parts necessary to gain access to valve tappets
- Remove spark plugs to ease turning engine over
- Turn engine flywheel by hand until left intake valve opens and closes
- Continue turning until TC mark on flywheel aligns with TC mark on gear cover
- Insert correct feeler gauge between valve stem and tappet
- Feeler gauge should pass freely; thicker gauge should not
- Turn adjusting screw using 7/16-inch wrench to obtain correct clearance
- Rotate engine one complete revolution and repeat for right cylinder
- Replace all removed parts and tighten securely
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Intake valve clearance: 0.008 in. (0.20 mm)
- Exhaust valve clearance: 0.013 in. (0.33 mm)
- Adjust only at ambient temperature
Full service-parts list: Cummins/Onan B48 →
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.