Product Description
Cummins 4089976 — Genuine Piston & Ring Kit (.020 Over) for ISB 5.9L (305 HP)
MPN: 4089976 | Also Known As: piston kit, .020 overbore, +0.50 mm piston | Supersedes/Cross-Refs (ID): 4089183 (replaced by 4089976), PAI 111545-100
Genuine Cummins piston kit engineered for the 2003–2004 5.9L ISB common-rail (305 HP) configuration. This kit services one cylinder and includes the piston, rings, pin, and retainers. .020" over (+0.50 mm) size—machine work required. Sold individually; 6 kits required per engine.
Features & Benefits
- OE bowl & compression spec tailored to 2003–2004 305 HP ISB 5.9L calibration.
- Matched ring pack for optimal sealing and reduced oil consumption.
- Hardened wrist pin & retainers included for a complete cylinder solution.
- .020" over (+0.50 mm) sizing to restore proper clearances after boring/honing.
- Genuine Cummins materials and QC for longevity and reliability.
Verified Fitment (Automotive)
| Year Range | Engine | Chassis |
|---|---|---|
| 2003–2004 | Ram 5.9L ISB (24V Common-Rail, 305 HP spec) | Ram 2500/3500 |
Industrial/Off-Highway: Used primarily on Tier 2 ISB/QSB 5.9 applications (verify by ESN/CPL before ordering). Some retailers index this kit against 4B/ISB families—always confirm by ESN for non-automotive engines.
Compatibility Notes:
- 305 HP only: Intended for 2003–early 2004 305 HP calibrations. Not for certain 2004 California emissions trucks.
- .020" over requires machine work (bore/hone) and precise piston-to-wall clearance per Cummins spec.
- For standard bore 2003–2004 use P/N 4089950. For 2004.5–2007 applications, use later-design pistons specific to those years.
- Helpful CPL references seen with this family: 2998, 8213 (verify).
Specifications
- Type: Piston & Ring Kit (one-cylinder service)
- Size: .020" over / +0.50 mm
- OE Part Number: 4089976
- Cross-References (ID): 4089183 (replaced by 4089976), PAI 111545-100
- Quantity Required: 6 per engine (sold individually)
Often Paired With
- Standard-bore alternative: Cummins 4089950 (03–04)
- Other oversizes: 4089977 (.040" over) for 03–04
- In-frame essentials: head gasket set, rod/main bearings, oil pump, injector sealing washers
- Machine shop tools: ring compressor, cylinder hone/boring, precision measuring set
What’s In The Box
- (1) Piston (.020" over)
- (1) Piston ring set (matched to piston)
- (1) Wrist pin (hardened)
- (2) Pin retainers/locks
Installation Tips
- Measure existing bore and follow Cummins clearances after boring/honing.
- Check deck height, piston protrusion, and ring end gaps; file-fit rings as required.
- Verify bowl orientation and arrow/markings relative to the combustion chamber.
- Replace or clean piston cooling nozzles and ensure oil passages are free of debris.
- Always confirm application via ESN/CPL before ordering.
FAQ
WILL THIS FIT MY 2003–2004 5.9L CUMMINS RAM?
Yes—4089976 is the .020" over piston kit for 2003–2004 305 HP ISB 5.9L common-rail applications. Some 2004 CA-emissions trucks differ—verify by VIN/ESN.
HOW MANY KITS DO I NEED?
Six. Each kit services one cylinder; order 6 for a complete engine.
IS MACHINE WORK REQUIRED FOR .020" OVER?
Yes. .020" over (+0.50 mm) requires boring/honing to spec and checking final clearances and ring end gaps.
WHAT IF I HAVE A STANDARD BORE?
Use 4089950 (standard bore) for 2003–2004 305 HP engines.
DOES THIS FIT CALIFORNIA-EMISSIONS 2004 TRUCKS?
Not typically. Certain 2004 CA-emissions calibrations use a different piston spec. Confirm by VIN/ESN before ordering.
IS THIS AN OEM CUMMINS KIT?
Yes—genuine Cummins piston, rings, pin, and retainers packaged for one-cylinder service.
