Cummins/Onan — Overhead Set (Valve Lash Adjustment)
Adjustments · valve train
From a Cummins/Onan owner's manual covering: 4B3.9, 4BT 3.9, 4BTA 3.9, 6B5.9, 6BT 5.9, 6BTA5.9, B3.9, B5.9, C8.3. Check it applies to your exact model before use.
Applies to: Cummins/Onan 4B3.9, Cummins/Onan 6BTA5.9, Cummins/Onan B5.9 engine
Before you start
- To avoid engine or timing pin damage, disengage the timing pin after locating top dead center.
Procedure
- Remove the valve cover.
- Locate top dead center (TDC) for cylinder No. 1 by barring the crankshaft while pressing on the timing pin.
- When the timing pin engages the hole in the camshaft gear, cylinder No. 1 is at TDC on the compression stroke.
- Set only valves indicated by the arrows (E = exhaust, I = intake).
- Holding the locknut steady with the wrench, adjust the valve clearance with the screwdriver or Allen wrench.
- Tighten the locknut to 24 N*m [18 ft-lb], and measure the valve lash again.
- Mark the vibration damper, and rotate the crankshaft 360 degrees.
- Adjust the remaining valves as indicated; tighten locknuts to 24 N*m [18 ft-lb].
- Install the rocker lever covers and tighten the capscrews to 24 N*m [18 ft-lb].
Tools required
- 1/2-inch drive Amazon
- Engine Barring Tool, Part No. 3824591 Amazon
- Feeler Gauge Amazon
- 14-mm Wrench Amazon
- Flat-Blade Screwdriver or 5-mm Allen Wrench Amazon
- 15 mm 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.