Cummins switched from Unified National Fine (UNF) to purely metric on the ISX after 2005. If you try to use a 9/16" socket on an M12 bolt, you will strip the head. Use 18mm for the main housing bolts.
Do not just run a wrench down the line. The ISX requires a specific tightening sequence to prevent the housing from "crocking" (distorting). Cummins Isx Flywheel Housing Torque Specs
Do not tighten the bolts in a circle. You must follow a crossing pattern to ensure even pressure distribution. Cummins switched from Unified National Fine (UNF) to
While official manuals vary slightly on exact bolt numbering, the industry-standard practice for the Cummins ISX flywheel housing is a "Outside-In, Star Pattern." (Note: If the housing has bolt holes on
The Pattern:
(Note: If the housing has bolt holes on the very top flange or bottom pan rail, tighten the main housing bolts first using the sequence above, then tighten the flange bolts to the same specification.)