Cummins/Onan 4.0BF-1R/9500 — Tappet Adjustment (Valve Clearance)

For the Cummins/Onan 4.0BF-1R/9500.

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Procedure

1. Remove all parts necessary to gain access to valve tappets.
2. Remove spark plugs to ease the task of turning the engine over by hand.
3. Use the engine flywheel to turn the engine over slowly by hand until the left hand intake valve opens and closes. Continue turning the flywheel until the TC mark is on the top and lined up with the TC mark on the gear cover. Both valves should be closed.
4. For the intake valve, a 0.003 inch thickness gauge should just pass between valve stem and tappet.
5. For the exhaust valve, a 0.010 inch thickness gauge should just pass between valve stem and tappet.
6. To correct the valve clearance, use a 7/16 inch open end wrench to turn the adjusting screw. A 9/16 inch open end wrench is required to hold the tappet while turning the adjusting screw.
7. To adjust valves on the right hand cylinder, turn engine one complete revolution and again line up mark on the flywheel and the TC mark on the gear cover. Then follow adjustment procedure given for left hand cylinder.
8. Replace all parts removed in Step 1. Tighten all screws securely. Torque manifold bolts to specified torque.

Source: manual:965-0515 Onan 4kwBF RV Genset Major Service manual (09-1973).pdf. Figures and steps are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.