Basic question here, but Is an F-7 basically the exact same loco (minus the body differences) as a GP-7? In other words the same motors/same performance/same fuel capacity?
Yes, engine, generator,motors,air compressor,trucks are all the same. Minor differences in couplings for the air compressor and the auxiliary generator . The F-7 air compressor was towards the front and used a grid coupling from the main generator The GP-7 air compressor was in the rear with rubber coupling bushings. The electrical cabinets were arranged differently.
The GP7 has the same basic internals has the F7. Same 567B prime mover, same D27 traction motors. Fuel capacity varied on the F7(1200-1500 gallon). The GP7 had more options with anywhere from 800 gallons - 2200 gallons(the air tanks could be moved to the roof, freeing space between the trucks). The early GP7's had the same 'ratchet' style throttle where you could only pull back to the next notch, and had to release before you could advance it another notch. Later GP7 when to a throttle that you could 'wipe', very useful for kicking cars.
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
The GP7 also had Switch mode, which helped a lot with the kicking. When working properly, notch 2 would be all you need. The 2 GP7 I have run were rebuilt built by the Santa Fe, with new style control stands installed, so I haven't run one where R2D2 is still in place. GP7 control stand GP7 operating manual
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com
One point to be aware of, many GP7s were built with the 6BL brake system intending to use them singly on branchlines. This caused problems when trying to use them with F7s on the mainline as the F units were equipped with the 24RL brake valve. EMD in its Engineering documents lists two different types of GP7s, a "GP7" with no suffix which indicates that the locomotive was built with the 6BL brake valve, and the "GP7R" indicating that it was built with the 24RL brake valve. This system carried over to the GP9 series, but late built GP9s added a third variant, the "GP9L" indicating that it was built with the newest 26L brake valve.
John Beaulieu
Interesting, thanks.
The GP7 came in a more switch engine like configuration also, with functions controlled by load regulator arms. To quote the operating manual:
"When the load regulator arm is in minimum field (4 o'clock), position, one finger of the plate moves LRS switch down. An open interlock on LRS prevents the shunt field contactor from closing. At the same time, a closed interlock on LRS energizes LRC, which partially establishes the circuit for the throttle controlled "Teaser" circuit. With the switch in this position, the amount of battery field current is varied by each throttle position, Fig. 1-4. When load regulator arm reaches mid-position (12 o'clock) a second finger moves LRS to opposite position. This allows the shunt field contactor to close, making main generator excitation normal, and cuts out the throttle controlled" Teaser" circuit. LRS switch will stay in this position until load regulator arm returns to full minimum field position, Fig. 1-5. When load regulator arm reaches maximum field (8 o'clock) position, the third finger closes the other tumble switch FTS, changing the motor connections from series-parallel to parallel, Fig. 1-6. FTS will open as the load regulator arm moves back away from maximum field, but the motor connections will stay in parallel until the backward transition relay is energized by approximately 2500 amperes main generator current. When the throttle is closed to idle, all P contactors open, and the S contactors close. As the throttle is reopened, the motor connections will be series-parallel, remaining so until the load regulator arm reaches maximum field, when the transition cycle is repeated".
There was a switch on control stand that, when down, prevented transition from taking place.
All of the Rock Island original freight service GP7's had the simple two step transition. Their steam generator equipped GP7's had the four step like the F7. The RI GP7 and most GP9 had 6BL air brakes. They were never modified to be able to lead HSC (E3,E6), 8ET (FT) and 24RL equipped units, they could only trail them because a special pipe was added right rear and left front to HSC (unsure about 8ET) and 24RL units.
The Soo Line modified their 6BL geeps to be able to lead or trail a 24RL unit as did most roads.
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