Product Description
Cummins 4089977 — Genuine Piston Kit (.040 in / 1.00 mm Over) for ISB 5.9L 305 HP
MPN: 4089977 | Also Known As: piston kit .040 over, 1.00 mm over piston kit | Sold: individually (6 required per engine)
Genuine Cummins piston kit sized for 0.040" overbore (1.00 mm), engineered for the 5.9L ISB common-rail 305 HP configuration. Ideal for rebuilds where cylinders are bored/honed .040" over. Includes piston, wrist pin, pin retainers, and ring set.
Features & Benefits
- OE piston crown & skirt design matched to the 305 HP ISB combustion profile.
- Precision 1.00 mm (.040") oversize for properly machined cylinders.
- Complete kit: piston, hardened wrist pin, retainers (circlips), and ring set.
- Quiet operation & durability with OEM materials and coatings.
- Built to Cummins standards for long service life when installed per spec.
Verified Fitment (Automotive)
| Year Range | Engine | Chassis |
|---|---|---|
| 2003 (HO) | Ram 5.9L ISB 24V Common-Rail 305 HP (High Output) | Ram 2500/3500 |
| Early 2004 (Federal) | Ram 5.9L ISB 24V Common-Rail 305 HP (Federal emissions) | Ram 2500/3500 |
Industrial/Off-Highway: Used primarily on Tier 2 ISB/QSB 5.9 configurations — verify by ESN/CPL prior to ordering.
Compatibility Notes:
- This kit targets the 305 HP calibration. For 2003, only the HO trucks were 305 HP; for early 2004, federal-emissions trucks were 305 HP. California-emissions 2004 trucks are not compatible.
- Measure bore after machining and confirm .040"/1.00 mm over before purchase. Piston-to-wall and ring gaps must be set to spec.
- If you need other oversizes, see related .020" (M-4089976) kits and standard-size options.
Specifications
- Type: Engine piston kit (.040"/1.00 mm oversize)
- Engine: Cummins ISB 5.9L (common-rail), 305 HP configuration
- Contents: piston, wrist pin, pin retainers, ring set
- Quantity Required: 6 per engine (sold individually)
Often Paired With
- Other oversizes/sets: .020" over (e.g., 4089976 equivalents), standard-size options
- Bearings: rod & main bearings matched to crankshaft condition
- Gasket set & head bolts/studs: top-end set and fasteners for reassembly
- Machine shop services: bore & hone with torque plates, deck checks, ring end-gap verification
What’s In The Box
- (1) Genuine Cummins Piston (.040"/1.00 mm over)
- (1) Wrist pin
- (2) Pin retainers (circlips)
- (1) Piston ring set
Installation Tips
- Confirm engine ESN/CPL and 305 HP calibration before ordering.
- After machining, measure bore and set piston-to-wall clearance per Cummins spec.
- File-fit rings and verify end gaps in the actual bores; stagger ring gaps on assembly.
- Check piston protrusion and valve relief clearance; verify head gasket thickness as required.
- Replace oil and filter after initial break-in; re-torque/re-check as applicable.
FAQ
WILL THIS FIT MY 2003–2004 5.9L CUMMINS?
It fits the 305 HP ISB calibration: 2003 HO trucks and early-2004 federal-emissions trucks. It does not fit 2004 California-emissions trucks. Verify by VIN/ESN.
WHAT SIZE IS THIS PISTON KIT?
It’s a .040" over (1.00 mm) piston kit. Your cylinders must be bored/honed to this oversize.
WHAT COMES IN THE KIT?
Piston, wrist pin, pin retainers (circlips), and ring set — sold individually. Order 6 for a complete engine.
DO YOU HAVE OTHER OVERSIZES?
Yes — .020" and standard-size kits are available under different part numbers. Contact us with your ESN/CPL.
IS THIS A GENUINE CUMMINS PART?
Yes — 4089977 is a genuine Cummins piston kit. We also carry Interstate-McBee equivalents (M-4089977) if requested.
