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.
: Always tighten bolts in a crisscross pattern to ensure even pressure. torque spec for flywheel bolts on isx cummins 251 updated
| Component | Torque | Notes | | :--- | :--- | :--- | | ISX Flywheel Bolt (251) – Standard | | Wet, 3 steps | | ISX Flywheel Bolt (251) – TTY | 265 lb-ft + 90° | Do not reuse | | Flywheel Housing to Block (251) | 44 lb-ft | M12 bolts | | Starter Motor Mounting Bolts | 65 lb-ft | Loctite 242 | | Clutch Pressure Plate (if equipped) | 55 lb-ft | Cross pattern | The term “251” refers to the SAE housing
Before final assembly, it is good practice to push the crankshaft toward the front of the engine to eliminate end clearance while checking for runout. Getting the flywheel torque wrong is dangerous, but
Always consult the current Cummins Quickserve online manual for your specific ESN (Engine Serial Number). If your engine uses a dual-mass flywheel or an automated manual transmission (AMT), the spec may differ due to different bending loads. For the standard ISX with a single-plate clutch and the 4921514 bolt, 251 N·m + 90° is the final answer.
Finalize the torque by tightening all bolts in the same pattern to the final 185 ft-lbs (250 N•m) JustAnswer Related Component Torque Specs
To correctly apply this spec, one must follow the "Cummins 5-Step Process" for the ISX: