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)

Industrial/Off-Highway: Used primarily on Tier 2 ISB/QSB 5.9 configurations — verify by ESN/CPL prior to ordering.

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.