Torque Spec For Flywheel Bolts On Isx Cummins 251 Updated

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:

These bolts secure the flywheel to the crankshaft. This is where the "updated" spec is critical due to the Dual Mass Flywheel design. torque spec for flywheel bolts on isx cummins 251 updated

For Dual Mass Flywheel (Common on ISX CM2250 / X15):

For Solid Flywheel (Older ISX / Clutch Brake applications): The term “251” refers to the SAE housing

An essay on this torque spec would be incomplete without warning about the consequences of deviation:

Cummins moved to Torque-To-Yield (TTY) bolts on late-model ISX (CM2350, X15). If your bolt has a reduced shank or a painted dot on the head, it is TTY. These bolts secure the flywheel to the crankshaft

Warning: Do not reuse TTY bolts. If you have an updated ISX 251 (2017+), buy a new bolt kit (P/N 3901388).

A: Log into Quickserve, navigate to Engine > Flywheel and Housing > Mounting. Look for revision date 2022 or later. The old PDFs still show 250 lb-ft; ignore them. Use the interactive torque tool which now defaults to 265 lb-ft.

| Engine Model | Flywheel Bolt Size | Updated Torque Spec | |--------------|--------------------|----------------------| | ISX (Pre-2007, 12-bolt) | M14 | 110 lb-ft + 60° | | ISX 251 (CM2250, CM2350) | M16 x 2.0 | 125 lb-ft + 90° | | X15 (Performance series) | M16 x 1.5 | 150 lb-ft + 75° |