Cummins/Onan — Cylinder Head Gasket Replacement
Maintenance
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan NHC-NHCV engine
Before you start
- Do not torque or remove heads when hot. Warpage may occur. Gasket surface must be below 100°F before removal.
- Asbestos gaskets contain fibers that when airborne can be harmful to your health. Use a respirator.
Procedure
- Remove cylinder head bolts with 1/2 inch socket; lift heads off.
- Clean out all carbon deposits without damaging sealing edges.
- Use new head gaskets and clean head and block surfaces thoroughly.
- Place gasket on cylinder head and align stud holes.
- Install cylinder head on engine with gasket.
- Install compression washers and hardened washers as shown.
- Torque nuts in sequence to 5 ft-lb, then 10 ft-lb, then specified torque.
- Recheck all nuts for correct torque and retorque a second time.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Cylinder head nuts cold: 18-20 FridayParts $25.20 ft-lb (24-27 Nm) asbestos without compression washers
- 13-15 ft-lb (18-20 FridayParts $25.20 Nm) asbestos with compression washers
- 14-16 Amazon eBay FridayParts $135.00 ft-lb (19-22 Amazon eBay FridayParts $39.99 Nm) Graphoil without compression washers
- 11-13 FridayParts $27.79 ft-lb (15-18 Nm) Graphoil with compression washers
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.