Product Description
Cummins 4955859 OEM Main Bearing Set (.040 Under Size / 1.00 MM) – 5.9L/6.7L ISB (1989–2018)
The Cummins 4955859 OEM Main Bearing Set (.040 Under Size / 1.00 MM) is a genuine Cummins crankshaft main bearing kit designed for 5.9L and 6.7L B-Series and ISB diesel engines from 1989–2018. Engineered for crankshafts that have been precision-ground .040 inch (1.00 mm) undersize, this OEM bearing set restores proper oil clearance, load capacity, and crankshaft support during engine rebuilds and overhauls. Genuine Cummins bearings are manufactured to strict OE specifications to ensure optimal lubrication, reduced friction, and long-term durability.
Whether you are rebuilding a 12-Valve Cummins, 24-Valve Cummins, Common Rail 5.9L, or 6.7L ISB engine, the 4955859 bearing set provides the precision fit and reliability required for professional engine machining and performance diesel rebuilds. This bearing set is intended exclusively for crankshafts that have been machined .040 inch (1.00 mm) under standard dimensions.
Features
- Genuine Cummins OEM main bearing set
- Designed for .040 inch (1.00 mm) undersize crankshafts
- Restores proper crankshaft oil clearance
- OE-quality materials and manufacturing standards
- Supports factory oil pressure and lubrication performance
- Ideal for complete engine rebuilds and overhauls
- Compatible with 5.9L and 6.7L Cummins B-Series engines
- Precision-engineered for long service life and durability
- Trusted by professional engine builders and machine shops
- Designed for heavy-duty diesel applications
Fitment
- 1989–2002 Dodge Ram 2500 & 3500 5.9L Cummins 12-Valve and 24-Valve
- 2003–2007 Dodge Ram 2500 & 3500 5.9L Common Rail Cummins
- 2007.5–2018 Ram 2500 & 3500 6.7L Cummins ISB
- 5.9L Cummins B-Series industrial engines
- 6.7L Cummins ISB industrial applications
- Agricultural, construction, marine, and off-highway B-Series applications
Note: This bearing set is intended for crankshafts that have been machined .040 inch (1.00 mm) undersize. Crankshaft measurements should always be verified by a qualified machine shop before ordering or installation.
What's Included
- Cummins 4955859 OEM Main Bearing Set
- Upper and lower main bearing shells
- OEM Cummins packaging
Specifications
- Manufacturer: Cummins Genuine Parts
- Part Number: 4955859
- Bearing Type: Main Bearing Set
- Bearing Size: .040 Under Size (1.00 MM)
- Engine Compatibility: 5.9L and 6.7L Cummins B-Series / ISB
- Engine Years: 1989–2018
- Application: Engine Rebuild and Overhaul
- Purpose: Crankshafts Ground .040 Inch Under Standard Size
- OEM Replacement: Yes
- Material: Cummins OE Bearing Material
- Package Weight: Approximately 2.5 lbs
Cross Reference Numbers
4955859, Cummins 4955859, 1.00MM Main Bearing Set, .040 Under Main Bearings, Cummins B-Series Main Bearings, Cummins ISB Main Bearings, 4938936, 4938940, 4938952
FAQ
What does .040 under size mean?
.040 under size means the crankshaft journals have been machined .040 inch (1.00 mm) smaller than factory specifications. This bearing set restores the proper oil clearance required after crankshaft grinding.
Will these bearings fit a standard crankshaft?
No. The Cummins 4955859 bearing set is specifically designed for crankshafts that have been ground .040 inch (1.00 mm) undersize. Always verify crankshaft measurements before ordering.
Do these fit both 5.9L and 6.7L Cummins engines?
Yes. This bearing set is commonly used in 1989–2018 Cummins B-Series and ISB engines when a .040 under crankshaft bearing size is required.
Should main bearings be replaced during an engine rebuild?
Yes. During a complete overhaul, main bearings should be replaced to ensure proper crankshaft support, oil pressure, and long-term engine reliability.
Are these genuine Cummins bearings?
Yes. Part number 4955859 is a genuine Cummins OEM main bearing set manufactured to original equipment specifications.
Can I install these without measuring the crankshaft?
No. Crankshaft journal measurements should always be confirmed by a machine shop before selecting undersize bearings to ensure proper bearing clearance and engine longevity.
