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Common maintenance events on the Allison 250 C20
If there are roller bearings installed, the pinion gear should come out more easily. However, be careful not to have the roller bearings fall apart in your hands! Turn the cover over again and remove the N1 gear train. The special pliers that Allison designed (P/N 6796966) are really helpful when removing and installing the fuel control drive gear.
A good technique for this gear is to stand the cover on its side with the fuel control gear at the top. With the special pliers in your left hand, you can actually see the tangs of the circlip, so it's easier to get the pliers on them. Also, with the cover on its side you don't have to overcome the weight of the gear, and it won't slip back into place before you let go of the pliers.
Remember that you only have to use the pliers until the gear has moved forward enough so that the circlip is away from the circlip groove. Keep in mind that the bearings on the FCU gear could have worn grooves into the bearing cage from spinning. This will mean that a bit of force might be required to remove the gear.
With all of the gears removed from the cover, carefully inspect each ball of each bearing. The torquemeter roller bearing can come apart, so hold the outer race and gently tap the assembly on the bench to encourage the rollers to fall inwards as much as possible.
Once separated, make sure the rollers don't lose their position or orientation. All of the bearings can be given a good visual inspection while installed on their shafts.
Common Maintenance Events on the Allison 250 C20
By Jim Taylor
February 1998
To remove bearings, it's always best to use the correct Allison special tooling. Used properly, the Allison tools will reduce the risk of damaging the bearings or the gearshafts that they're installed on. Most AMCs will rent or lend out special tools to their customers. Should you find yourself stuck, you can get by with a standard clam-shell puller and two pieces of angle iron. Where the gear diameters are larger than the bearing, or the clamshell puller, use the angle iron and some blocks to build a support bridge around the gear while pressing off the bearing.
It's most important to make sure the puller is only contacting the inner race of the bearing to be removed. Scrap the bearing if you think any force has been inadvertently put on the outer race or the balls of the bearing during its removal.
