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Inside your AEG (automatic electric gun) is a gearbox in which a motor turns a series of gears to cock the piston. The gears inside an AEG will be the sector gear, spur gear, and bevel gear. These gears turn at very high speeds and their efficiency and durability are greatly affected by the friction and fitting of the gears in relation to one another. Gearboxes, bushings/bearings, and gears are manufactured in mass and can vary every so slightly in tolerances. These components must work together so their fitment is crucial to ensure your gearbox and its components have a long life.
The gears all interact with each other in a vertical fashion, but how they are positioned horizontally is where the most friction can be observed. When the gearbox is assembled by a manufacturer, the technicians ensure these gears do not rub each other on the horizontal axis. When the gears are installed into the gearbox, the tolerances and spacing between the gears is checked and if the gears are tight along that axis then shims are added to give the gears adequate clearances to turn. Shims are tiny metal discs that come in varying thicknesses that are used to space the gears inside the gearbox and make them clear the gearbox walls and other gears to provide a smooth operation.
The act of shimming a gearbox is not easy to learn and requires patience with a fully disassembled gearbox. We offer tech work to service and upgrade most popular AEGs.
Q: How long should shims last?
A: Shims can be made of anything from brass to steel and do not wear out of break. It would be exceptionally rare but shims should not fail. Bad shimming is more of the concern as too many shims will cause binding which makes friction. Friction creates more wear and tear on gears and creates more strain on the electrical system by drawing more amperage.
Q: How do I spot bad shimming?
A: Stock AEGs from the factory will come with adequate shimming for the gun to function, otherwise they will not be sellable and are obvious the moment they are first used. Bad shimming can be noticed by high pitched sounding gears in opration, though this is not to be confused with incorrect motor height which should be checked first.
Q: How can I correct the shimming?
A: Reshimming the gearbox involves tearing down the entire gearbox, cleaning all of the grease out, and reshimming all the gears and checking the tolerances. This is not required of working guns out of the factory though since they are adequately shimmed at the factory. If you are changing components such as the gears or bushings/bearings or even the shell itself, you will have to shim the gears. If you already have your gearbox open this is a good time to check the shimming to see if it can be optimized rather than just be adequate. Each gear is to individually installed into the gearbox, tyically starting with the spur gear and checked to make sure that it can freely spin (with no piston or spring) with no load. If the gear makes contact with the gearbox or drags, add the thinnest shims possible and work your way up. Then install the bevel or sector gear and make sure there is adequate clearance between that and the spur gear and also the other half of the gearbox as it is closed.