To correctly apply this spec, one must follow the "Cummins 5-Step Process" for the ISX:
These bolts secure the flywheel to the crankshaft. This is where the "updated" spec is critical due to the Dual Mass Flywheel design.
For Dual Mass Flywheel (Common on ISX CM2250 / X15): torque spec for flywheel bolts on isx cummins 251 updated
For Solid Flywheel (Older ISX / Clutch Brake applications):
| Mistake | Consequence | Updated Fix | | :--- | :--- | :--- | | Using 250 lb-ft | Under-torqued by 15 lb-ft; bolt fatigue in 10k miles | Increase to 265 lb-ft as of FSB 140514 | | Dry threads | Achieve only 210 lb-ft actual clamp load | Lubricate with engine oil | | Reusing old bolts | Over-stress cracks leading to shearing | Replace TTY bolts every time | | Skipping the 90° | Loose flywheel, broken housing | Use angle gauge, not “eyeball” | To correctly apply this spec, one must follow
For the Cummins ISX (CM570, CM870, CM871, CM2250, CM2350) equipped with the 251mm (10 inch) flywheel housing:
Critical Update (2024-Present): Older literature sometimes listed 250 lb-ft. The updated Cummins FSB (Field Service Bulletin) #140514 revises this to 265 lb-ft + 90° for all ISX engines using the 251 flywheel with original equipment bolts. For Solid Flywheel (Older ISX / Clutch Brake applications):
A: Over-torquing (exceeding 300 lb-ft or 120° angle) will stretch the bolt beyond yield. The bolt will snap the next time you engage the clutch at 1,800 RPM.
The term “251” refers to the SAE housing size (SAE #1) but specifically the flywheel mounting pattern. The ISX uses a heavy dual-mass or solid flywheel with a specific bolt circle. The 251mm housing is standard on most over-the-road ISX engines (Peterbilt, Kenworth, Freightliner). Getting the flywheel torque wrong is dangerous, but confusing it with the flexplate torque (used in motorhomes or industrial pumps) is catastrophic.
Do not confuse this with:
Never install flywheel bolts dry. The 265 lb-ft spec assumes wet threads with engine oil.
