Product Description
Cummins 3903857 — Genuine Vibration Damper / Flywheel Mounting Bolt for 5.9L (6BT/ISB)
MPN: 3903857 | Also Known As: hex flange head cap screw, harmonic balancer bolt, damper bolt, flywheel bolt
Genuine Cummins hex-flange bolt engineered for critical crankshaft interfaces. Commonly used to secure the harmonic balancer (vibration damper) and, in certain applications, the flywheel/flexplate on 5.9L B-Series engines. Direct-fit for 1989–2002 5.9L (12V & 24V VP44). Sold individually.
Features & Benefits
- OE-grade fastener with correct flange head and shank engagement for high clamp load.
- Designed for B-Series crankshaft damper/flywheel interfaces to maintain alignment and prevent loosening.
- Heat-treated for strength and fatigue resistance under high torsional loads.
- Exact fit—no guesswork on length or thread pitch versus generic hardware.
- Backed by Cummins for proven reliability.
Verified Fitment (Automotive)
| Year Range | Engine | Chassis |
|---|---|---|
| 1989–1993 | 5.9L 12V (6BT) | Ram 2500/3500 |
| 1994–1998 | 5.9L 12V (6BT) | Ram 2500/3500 |
| 1998.5–2002 | 5.9L 24V ISB (VP44) | Ram 2500/3500 |
Industrial/Off-Highway: Used primarily on BS3 5.9L B-Series; may appear on select 4B/6B applications. Verify by ESN.
Compatibility Notes:
- This listing targets 1989–2002 5.9L trucks. Later 5.9L/6.7L applications can use different hardware—confirm by VIN/ESN.
- Quantity needed (typical): 4 bolts for the vibration damper. Flywheel/flexplate quantity varies by transmission—confirm per service manual.
- Replace removed bolts with new OE hardware when servicing the damper or flywheel.
Specifications
- Type: Hex flange head cap screw (damper/flywheel service)
- OE Part Number: 3903857
- Thread Size: M12 x 1.25
- Under-head Length (approx.): ~36 mm (1.425 in)
- Quantity Required: Sold individually (order set as needed)
What’s In The Box
- (1) Genuine Cummins Hex Flange Head Bolt (3903857)
Installation Tips
- Clean threads and mating surfaces; use new bolts during damper or flywheel service.
- Apply thread locker only if specified by the service manual.
- Torque in a star pattern to factory spec; recheck after initial heat cycle if procedure calls for it.
FAQ
WILL THIS BOLT FIT MY 1989–2002 5.9L CUMMINS RAM?
Yes—3903857 is an OE hex-flange bolt used on BS3 5.9L B-Series applications, including 1989–2002 12V & 24V trucks. Always confirm by VIN/ESN.
HOW MANY BOLTS DO I NEED FOR THE HARMONIC BALANCER?
Typically 4 bolts secure the vibration damper on 5.9L B-Series engines. Order the correct quantity for your service.
IS THIS ALSO A FLYWHEEL/FLEXPLATE BOLT?
3903857 is referenced for damper and some flywheel/flexplate uses on B-Series. Transmission and year may change hardware—verify by VIN/ESN or service manual.
WHAT IS THE THREAD SIZE?
M12 x 1.25. Length is approximately 36 mm (1.425 in) under the head.
IS THIS A GENUINE CUMMINS PART?
Yes—OE Cummins 3903857.
