Cummins/Onan B43 / B48 — Valve Tappet Adjustment
Adjustments · valve system
For the Cummins/Onan B43 / B48, from the Cummins/Onan service manual.
Applies to: Cummins/Onan B48
Before you start
- Adjust the valve clearance only when engine is at ambient temperature.
Procedure
- Remove ignition key to prevent accidental starting.
- Remove all parts necessary to gain access to valve tappets.
- Remove spark plugs to ease turning the engine over by hand.
- Place a socket wrench on the flywheel capscrew and rotate crankshaft clockwise until left intake valve opens and closes; continue until TC mark on flywheel lines up with TC mark on gear cover (left pi
- Verify left intake and exhaust valves are closed and there is no pressure on valve lifters.
- Correct feeler gauge should pass freely between valve stem and tappet; a 0.002 inch (0.05 mm) thicker gauge should not.
- To correct clearance, use a 7/16-inch open end wrench to turn adjusting screw; a 9/16-inch (14 mm) open end wrench is required to hold the tappet.
- To adjust valves on the right hand cylinder, turn engine one complete revolution and again line up the marks.
- Replace all parts removed and tighten all screws securely; torque manifold bolts to specified torque.
Tools required
- feeler gauge Amazon
- 7/16-inch open end wrench Amazon
- 9/16-inch (14 mm) open end wrench Amazon
- socket wrench Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Valve clearance intake 0.005 inch (0.13 mm) cold
- Check and adjust at least every 200 operating hours
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.