Cummins/Onan 4.0 BF-1R/9500 — Tappet Adjustment
Adjustments · Valve tappets
For the Cummins/Onan 4.0 BF-1R/9500, from the Cummins/Onan service manual.
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Before you start
- Adjust valve clearance only when engine is at ambient temperature.
Procedure
- Remove parts to gain access to valve tappets and remove spark plugs.
- Turn engine over slowly by hand using flywheel until left hand intake valve opens and closes.
- Continue turning until TC mark aligns with TC mark on gear cover; both valves closed.
- Intake: a .003 inch thickness gauge should just pass between valve stem and tappet.
- Exhaust: a .010 inch thickness gauge should just pass between valve stem and tappet.
- Use 7/16 inch open end wrench to turn adjusting screw; hold tappet with 9/16 inch wrench.
- Turn engine one complete revolution, realign TC marks, and repeat for right hand cylinder.
- Replace all parts removed and torque manifold bolts to specification.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Intake .003 inch (cold)
- Exhaust .010 inch (cold)
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.