Cummins/Onan — Cylinder Head Assembly Replacement

Repair & overhaul

From a Cummins/Onan service manual covering: C13 N6H, C13N6H, C17 N6H, C17N6H, C20 N6, C20N6H, RS13A. Check it applies to your exact model before use.

Applies to: Cummins/Onan C13 N6H, Cummins/Onan C17 N6H, Cummins/Onan C20 N6, Cummins/Onan RS13A

Procedure

1. Shut down and disable the generator set; disconnect the negative (–) cable first, then the positive cable.
2. Remove the necessary enclosure panels and service access panels (and oil cooler if needed) to access the cylinder head.
3. Remove the engine shield below the valve cover.
4. Remove the four valve cover mounting bolts, valve cover and valve cover gasket.
5. Remove rocker arms, rotating the engine first to ensure there is no valve spring pressure on the rocker arm being removed.
6. Remove the six cylinder head bolts and the cylinder head. Retain the two cylinder locating sleeves from each cylinder head.
7. Remove the head gasket and safely remove any gasket material left on the mating surface.
8. Install the locating sleeves and the new head gasket.
9. Install the new cylinder head assembly, tightening the bolts in the pattern shown to 50 Nm (36.9 ft-lb).
10. Apply Loctite 262 to the stud; attach the rocker arm and nut; tighten the nut to 8 - 12 Nm (71 - 106 lb-in).
11. Adjust the valve clearance and tighten the nuts together to 14 - 18 Nm (10.4 lb-in - 13.3 lb-ft).
12. Assemble the new valve cover gasket and valve cover; tighten the bolts to 8 - 12 Nm (71 - 106 lb-in).
13. Re-install the panels removed in step 2.
14. Re-connect the battery, positive terminal first, then the negative terminal; restore power to the AC accessories.
15. Test run the generator set with load if possible.

Full service-parts list: Cummins/Onan C20 N6 →

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.

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