Product Description
Genuine Cummins
Cummins 3920921 — P7100 Injection Pump Gear Nut
MPN: 3920921 | Also Known As: P7100 main shaft nut, gear retaining nut | Often Paired With: Lock Washer 3920922 (sold separately)
Why This Part
- ✓ OE gear retaining nut that secures the P7100 pump gear to the main shaft.
- ✓ Direct-fit hardware for 1994–1998 5.9L 12-valve (P7100).
- ✓ Restores proper clamp load after pump/gear service—don’t reuse damaged hardware.
- ✓ Built to Cummins specs for reliable torque retention.
OE Fit Critical Hardware Use New Lock Washer
Quick Specs
| Type | P7100 injection pump gear retaining nut (main shaft nut) |
|---|---|
| OE Part # | 3920921 |
| Related | Lock Washer 3920922 (recommended) |
| Qty Required | 1 per pump (sold individually) |
Verified Fitment (Automotive)
| Year Range | Engine | Chassis |
|---|---|---|
| 1994–1998 | 5.9L 12-Valve (6BT) with P7100 | Dodge Ram 2500/3500 |
Notes: For 12-valve engines with Bosch P7100 pump. Always verify by VIN/ESN and confirm pump model before ordering.
Often Paired With
- P7100 Lock Washer: Cummins 3920922 (use new washer at reassembly)
- Front gear cover seal & gasket if opened during service
- Service manual torque spec—always torque to factory specification
What’s In The Box
- (1) Genuine Cummins P7100 Gear Retaining Nut (3920921)
- Lock washer sold separately (3920922)
Install Tips
- Inspect gear/keyway and pump shaft threads; replace any damaged hardware.
- Use a new lock washer (3920922) and torque the nut to factory spec.
- Re-check timing marks and oil for debris after first heat cycle.
FAQ
WILL THIS FIT MY 1994–1998 12-VALVE?Yes—this is the OE gear nut for 5.9L 12-valve (P7100) trucks. Verify by VIN/ESN and pump model.
IS THIS THE MAIN SHAFT NUT FOR THE P7100?Correct—this nut retains the drive gear on the P7100 main shaft.
SHOULD I REPLACE THE LOCK WASHER?Yes—replace the lock washer (3920922) during reassembly for proper clamp load.
IS THIS A GENUINE CUMMINS PART?Yes—OE Cummins 3920921 for proper fit and durability.
WHAT IF MY TRUCK IS A 1998.5+ 24-VALVE?Those engines use different pump hardware. This nut is for 12-valve P7100-equipped trucks.
