Cummins/Onan — Valve Adjustment Procedure
Adjustments · Intake and exhaust valves
From a Cummins/Onan owner's manual covering: G 12, G28, G855, GTA12, GTA19, GTA28, GTA855. Check it applies to your exact model before use.
Applies to: Cummins/Onan G 12, Cummins/Onan G&855, Cummins/Onan GTA855
Before you start
- DO NOT USE THE OUTER MEMBER of the Vibration Damper to bar the engine.
Procedure
- Bar the engine in the direction of rotation until the No. 1 VS mark appears on the accessory drive pulley (GTA19 marks are on the vibration damper).
- In this position both intake and exhaust valves will be closed if the cylinder is in the firing position; if not, rotate the engine one complete revolution.
- Continue to rotate the engine until the VS marks line up with the marker on the engine block or engine water pump capscrew (GTA28).
- Adjust the crossheads first, then the valves, following the procedure in this section.
- Continue turning the crankshaft in the direction of rotation, adjusting one cylinder at a time until all cylinders have been adjusted.
- Two complete revolutions of the crankshaft are needed to adjust all intake and exhaust valves.
Tools required
- ST-747 Barring Tool Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- See Table #15-03 FridayParts $122.95 valve adjustment settings (cold set)
Full service-parts list: Cummins/Onan G 12 →, Cummins/Onan G&855 →
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.