Cummins/Onan — Cylinder Head Assembly (NHM)
Repair & overhaul
From a Cummins/Onan service manual — check it applies to your exact model before use.
Browse Cummins/Onan generators & specs →
Before you start
- Too much torque will flatten compression washers
- Recheck torque before engine has run 50 hours
Procedure
- Use new head gaskets; clean heads and block.
- Align gasket stud holes and install head on engine.
- Install flat washer, two compression washers and nut on top six studs.
- Install flat washer and nut on four bottom studs.
- Torque in sequence to 5 ft-lbs, then 10 ft-lbs, then specified torque.
- Recheck all nuts for correct torque.
Tools required
- torque wrench Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 14 ft-lb with compression washers
- 17 ft-lb without 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.