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Common maintenance events on the Allison 250 C20
The fuel control gearshaft is best installed with the cover lying horizontally. Use the specially designed pliers P/N 6796966. As the gear is lowered into position, bend down to the bench level and try to peek in from side to see when the circlip is at the circlip groove. To test the circlip for proper engagement, move one of the tangs from left to right. If the circlip is properly installed the other tang will follow the movement.
The pinion gear is to be the first N2 gear to be installed, followed by the PTO gear. Have the cover sit as level and as steady as possible. Then place the torquemeter thrust washer and bearing thrust plate so that the cut-outs line up with the keyway in the torquemeter insert. Use petrolatum to help keep the pieces in place.
Carefully maneuver the torquemeter gear into position while holding the torquemeter roller bearing in the gear. The idea is to place gear and the bearing into position without moving or disturbing the torquemeter thrust plate and thrust washer.
Now you can push the torquemeter shaft support through the roller bearing and into the torquemeter insert in the gearbox cover. Install the torquemeter nut and lockcup and just snug it up at this time. This will help in the assembly of the gearbox cover onto the housing — it's a little more comfortable torquing up the nut when there is a whole gearbox to hang on to.
Mating the cover and housing — It's advisable to use one of the approved sealants on the splitline to help avoid oil leaks from this area. However use it sparingly, as the excess will be squeezed into the gearbox where it will get into the oil system and eventually end up in either the scavenge oil filter or the main engine oil filter.
After reviewing your work, making sure all the safety wire has been done, and that all the pieces are in place. Place the housing in front of you so that the oil pump side is closest to you.
This is important because you'll want to use the three long studs located beside the oil pump on the splitline as guides for lining up the cover.
