Product Description
Cummins 4955857 — Main Bearing Set, .020" Undersize (0.50 mm)
MPN: 4955857 | Also Known As: main bearings, crankshaft main bearing set | Related Sizes: 4955855 (STD), 4955856 (.010 / 0.25 mm), 4955858 (.030 / 0.75 mm), 4955859 (.040 / 1.00 mm)
Why This Part
- ✓ OE bearing geometry & overlay for stable oil film and long service life.
- ✓ .020" undersize (0.50 mm) to match reground crank journals.
- ✓ Direct-fit for Cummins B-Series 5.9L (12V/24V) & ISB 6.7L with .020" regrind.
- ✓ Restores proper oil clearance, pressure, and durability after machining.
Quick Specs
| Type | Main bearing set (journal undersize .020" / 0.50 mm) |
|---|---|
| OE Part # | 4955857 |
| Fit Families | 5.9L 6BT (12V), ISB 5.9L (24V), ISB 6.7L |
| Includes | Upper & lower shells for all mains (verify thrust configuration by ESN) |
Verified Fitment (Automotive)
| Year Range | Engine | Chassis |
|---|---|---|
| 1989–1998 | 5.9L 6BT (12-Valve) | Ram 2500/3500 |
| 1998.5–2002 | 5.9L ISB (24-Valve VP44) | Ram 2500/3500 |
| 2003–2007 | 5.9L ISB (24-Valve Common-Rail) | Ram 2500/3500 |
| 2007.5–2018 | 6.7L ISB (24-Valve Common-Rail) | Ram 2500/3500 |
Notes: This is a .020" undersize main set for crankshafts machined .020" (0.50 mm) under. Always confirm by Engine Serial Number (ESN) and measured journal size.
Often Paired With
- Related Main Bearing Sizes: 4955855 (STD), 4955856 (.010 / 0.25 mm), 4955858 (.030 / 0.75 mm), 4955859 (.040 / 1.00 mm)
- Rod Bearings: match rod journal size to crank regrind
- Plastigage: verify final oil clearance during assembly
- Fresh oil & filter after first heat cycle
What’s In The Box
- (1) Genuine Cummins Main Bearing Set — .020" undersize (0.50 mm) — P/N 4955857
- Thrust bearing configuration varies by application; verify by ESN.
Install Tips
- Confirm crankshaft journals are reground to .020" under; polish and clean thoroughly.
- Measure housing bores and journal diameters; check oil clearance with plastigage.
- Torque main caps in sequence to factory spec; verify crank endplay per service manual.
FAQ
IS .020" THE SAME AS 0.50 MM?Yes—.020" undersize equals 0.50 mm undersize on the main journals.
WILL THIS FIT BOTH 5.9L AND 6.7L CUMMINS?Yes—this set covers 5.9L (12V/24V) and 6.7L ISB platforms when the crank is machined .020" under. Always confirm by ESN.
DO I NEED A REGROUND CRANK FOR .020" BEARINGS?Yes—.020" bearings require journals machined to the matching undersize. Do not install on a standard crank.
DOES THIS SET INCLUDE THRUST BEARINGS?Applications vary. Many B-Series engines use an integrated thrust at the center main—verify by ESN before assembly.
IS THIS A GENUINE CUMMINS PART?Yes—OE Cummins P/N 4955857 main bearing set (.020" / 0.50 mm).
