Cummins/Onan — Overhead Set (Valve Adjustment)
Adjustments · Valve train
From a Cummins/Onan owner's manual covering: B3.9, B4.5, B5.9. Check it applies to your exact model before use.
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Procedure
- Remove the rocker lever covers.
- Locate top dead center (TDC) for cylinder number 1.
- Rotate the engine clockwise until cylinder 4 (4-cylinder) or cylinder 6 (6-cylinder) intake rocker arm starts to open the intake valve.
- Adjust only the valves indicated, holding the locknut steady with a wrench and turning the screwdriver or Allen wrench.
- Tighten the locknut and measure the valve lash again.
- Mark the vibration damper and rotate the crankshaft 360 degrees.
- Adjust the remaining valves as indicated.
- Check the rocker lever covers for cracks and install them.
Tools required
- Feeler gauge Amazon
- Engine Barring Tool, Part Number 3824591 Amazon
- Screwdriver or Allen wrench Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Intake clearance 0.254 mm [0.010 in]
- Exhaust clearance 0.508 mm [0.020 in]
- Locknut torque 24 N·m [18 ft-lb]
Source: Cummins/Onan owner's 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.