Cummins/Onan Onan P4500i / P4500 — Checking and Adjusting Valve Lash
Adjustments · Engine/Valvetrain
For the Cummins/Onan Onan P4500i / P4500, from the Cummins/Onan operator's manual.
Applies to: Cummins/Onan Onan P4500i, Cummins/Onan P4500
Before you start
- Must be done when the engine is cold.
Procedure
- Remove rocker arm cover and gasket; replace gasket if damaged.
- Remove spark plug to ease rotation.
- Rotate engine to TDC of compression stroke.
- Confirm both rocker arms loose at TDC; rotate 360 degrees if not.
- Insert feeler gauge between rocker arm and push rod; check clearance.
- If needed, hold adjusting nut and loosen jam nut.
- Turn adjusting nut to obtain correct valve lash.
- Tighten jam nut to 106 in-lb (12 N.m) while holding adjusting nut.
- Recheck valve lash after tightening.
- Repeat for both intake and exhaust valves.
- Install rocker arm cover, gasket, and spark plug.
Tools required
- Feeler gauge Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Intake valve lash 0.09 ± 0.11mm
- Exhaust valve lash 0.11 ± 0.13mm
- Jam nut torque 8-12 N.m (106 in-lb)
Full service-parts list: Cummins/Onan Onan P4500i →, Cummins/Onan P4500 →
Source: Cummins/Onan operator'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.