Product Description
CUMMINS 3800785 OEM ENGINE PISTON KIT – ISB 5.9L 24V (1998.5–2002) – .040" OVERSIZE
The Genuine CUMMINS 3800785 .040" Oversize Piston Kit is engineered for the 1998.5–2002 ISB 5.9L 24-valve platform and delivers the exact OE machining, metallurgy, and durability required for a long-life engine rebuild. Oversize pistons are used when your cylinders require a .040” rebore during overhaul, ensuring proper wall clearance, sealing, and long-term reliability. This kit includes the matched Cummins piston, piston rings, wrist pin, and retainers, making it a complete OE solution for standardized fit and finish.
Whether you're restoring compression, repairing scoring, or completing a full ISB rebuild, using genuine Cummins pistons avoids the cracking, ring-land distortion, and coating failures seen with cheaper aftermarket copies. Maintain factory heat resistance, balance, and friction-control characteristics with the same components Cummins installs at the OEM level.
Key Features
- Genuine Cummins OEM piston kit for correct bore clearance and longevity.
- .040" oversize piston – designed for cylinders that have been rebored/honed .040”.
- Matched piston, rings, wrist pin, and retainers included for perfect OE assembly.
- Correct ISB combustion bowl design for proper spray pattern and efficiency.
- Ideal for full overhauls on 1998.5–2002 ISB 5.9L 24V engines.
Fitment Details
- Engine: Cummins ISB 5.9L 24-valve
- Model Years: 1998.5–2002
- Application: Dodge Ram 2500 / 3500 (24-valve)
- Bore Size: .040" oversize (requires machine shop cylinder rebore)
Always verify engine serial number (ESN) for correct piston selection, especially when mixing model-year transition engines.
Cross-Reference & Related Cummins Components
- CUMMINS 3802006 OEM PISTON KIT – STANDARD SIZE
- CUMMINS 3802008 OEM PISTON KIT – .020" OVERSIZE
- CUMMINS 3800791 OEM PISTON KIT – .060" OVERSIZE
These links are verified working Cummins products on CPPDiesel.com.
Installation Notes
- Pistons MUST match the cylinder bore after machining (.040” over).
- Check ring end gap per Cummins specifications during installation.
- Verify piston orientation (fuel bowl offset) before torquing rod bolts.
- Always inspect connecting rods for twist, bend, or big-end out-of-round.
- Oil squirters and cooling nozzles must be clean and unobstructed.
Specifications for cummins 3800785
| Attribute | Value |
|---|---|
| Brand | Cummins (Genuine OEM) |
| Part Number | 3800785 |
| Oversize | .040" (1.00 mm) |
| Includes | Piston, Rings, Wrist Pin, Retainers |
| Engine Compatibility | ISB 5.9L 24-Valve (1998.5–2002) |
| UPC | 193807155016 |
| GTIN | 193807155016 |
| Related Cummins Cross References | 3802006 (Std), 3802008 (.020), 3800791 (.060) |
| Shipping Weight | Approx. 2.4 lbs per piston kit |
| Shipping Method | Standard or expedited ground through CPP Diesel |
| E-Codes / Emissions | ISB light-duty diesel certification families (varies by ESN) |
| Prop 65 Warning | WARNING: This product can expose you to chemicals including engine oil residues known to the State of California to cause cancer and reproductive harm. See www.P65Warnings.ca.gov. |
| Country of Origin | As labeled by Cummins (varies by production batch) |
Frequently Asked Questions
IS THIS THE CORRECT PISTON KIT FOR MY 1998.5–2002 24-VALVE?
Yes — this kit is designed specifically for 1998.5–2002 ISB 5.9L 24-valve engines. Always confirm via engine serial number (ESN).
DOES THE KIT INCLUDE RINGS AND WRIST PIN?
Yes. The Cummins 3800785 kit includes the piston, rings, wrist pin, and retainers exactly as supplied from Cummins.
WHAT SIZE CYLINDER BORE DOES .040" OVERSIZE REQUIRE?
.040" oversize pistons require the machine shop to bore and hone the cylinder 0.040" (1.00 mm) over the standard diameter.
CAN I MIX DIFFERENT OVERSIZE PISTONS IN THE SAME ENGINE?
No. All cylinders should be measured and matched to the correct oversize. Each cylinder must use the piston that corresponds to that specific bore.
IS THIS A GENUINE CUMMINS OEM PISTON KIT?
Yes — CPP Diesel sells only genuine Cummins piston kits, not aftermarket copies.
