CUMMINS 4955859 OEM MAIN BEARING SET (.040 UNDER SIZE / 1.00 MM) – 5.9L/6.7L ISB (1989–2018)

Product Description

The Cummins 4955859 OEM Main Bearing Set (.040 Under / 1.00 mm) is a genuine Cummins undersize crankshaft bearing kit engineered for 5.9L and 6.7L ISB engines from 1989–2018. This main bearing set is designed for crankshafts that have been precision-ground to .040" (1.00 mm) undersize, offering factory-level load capacity, oiling performance, and long-term durability. When rebuilding a B-Series or ISB engine, installing genuine Cummins bearings ensures correct lubrication, reduced friction, and extended service life compared to aftermarket rebuild kits.

Ideal for full overhauls, professional machine shop builds, or any application requiring exacting OE tolerances, the 4955859 main bearing set helps restore factory oil pressure and structural integrity in high-mileage or previously failed engines.

Fitment

Automotive & Pickup Applications:

• 1989–2002 Dodge Ram 2500/3500 – 5.9L 12-Valve & 24-Valve Cummins
• 2003–2007 Dodge Ram 2500/3500 – 5.9L ISB Common Rail
• 2007.5–2018 Dodge Ram 2500/3500 – 6.7L ISB Cummins

Industrial, Agricultural & Off-Highway B-Series Engines:

• 5.9L B-Series (various displacements & ratings)
• 6.7L ISB (multiple emissions/ESN configurations)

Note: Because this bearing set is an undersize (.040 / 1.00 mm) application, machine shop measurement and crankshaft regrind confirmation are required.

Cross-Reference (Cummins-Only)

Related Cummins engine rebuild components:
• Cummins 3903924 OEM Timing Pin – 5.9L 12V
• Cummins 3904409 Valve Stem Guide – 51.75mm
• Cummins 3900267 Tappet Cover Bolt Grommet Seal

FAQ

What does “.040 under / 1.00 mm” mean on main bearings?

It means the crankshaft has been machined 1.00 mm smaller than OEM diameter. This bearing set restores proper oil clearance on a ground undersize crankshaft.

Do these fit both 5.9L and 6.7L Cummins engines?

Yes. This part number is used on 1989–2018 B-Series and ISB engines requiring .040 undersize main bearings.

Should all bearings be replaced during an engine rebuild?

Yes. Cummins recommends replacing mains, rods, and thrust bearings together for balanced wear and correct oiling.

Do these bearings include the thrust bearing?

This kit may include thrusts depending on Cummins packaging. Verify with your build requirements or add thrusts separately if needed.

What if my crankshaft is not exactly .040 under?

You must match bearing size to actual crankshaft grind measurement. Confirm dimensions with a machine shop before ordering.

Specifications for cummins 4955859