In 1978 CN began to reclassify some 8600 series units into hump (MH, 100 series) and yard (MY, 300 series) units.
In 1984 the remaining 100 series units were rebuilt and the rear cab door was changed so that it opened outwards and was hinged on the right and the cab windows on the driver's side were changed so that there were two smaller vertical windows above a horizontal rectangular window.
In 1984-5 twelve units from all four series (100, 300, 8500 and 8600) were rebuilt (most if not all at Moncton) into the 8700 series and two rebuild plates (one in each official language) were fixed on the right-hand frame below the rear of the cab . The rear cab door was changed so that it opened outwards and was hinged on the right and the cab windows on the driver's side were changed so that there were two shorter vertical windows (same size as left side) with a horizontal window below them. Dual sealed-beam headlights were fitted to those units that did not already have them and three chime horns were added, either mounted on the cab roof or somewhere between the stack and cab. Some 8700 units also had one or both of the side walkways extended so that the step is almost at the front.
All units were repainted after rebuilding and had orange on the front and rear of the cab and on the nose but the cab sides were black with gold and white numbers, the rest of the unit was black with an off-white CN logo, yellow reflective striping on the edge of the frame and white numbers on the rear of the cab on both sides above the widows.
The last S-13 was retired in 1997 and the longevity of these units perhaps indicates the superiority of the 251 engine over the 539 engine.