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Airsoft Electric Gun (AEG) or Electric Airsoft Gun Gearbox Guide

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A Closer Look at the Top Electric Airsoft Gun Gear Box Designs

Airsoft Electric Guns, also referred to as AEG’s or Electric Airsoft Guns, differ from most’ airsoft sniper rifles and cheap airsoft guns (LPEGs, ect) buy utilizing a motor and gear driven air pump system designed to fit in the internal receiver of an airsoft gun and fire airsoft BBs.  This is called a gearbox, or mechbox. Depending on the style of airsoft gun, various different models of airsoft electric gun gear boxes have been created to fit.  Some AEG gear boxes have inherent weaknesses and where necessary we’ll cover that. First lets get into the components that make up an electric airsoft gun.

Internal Components That Make Up an Electric Airsoft Gun’s Gearbox

While some internal airsoft components may differ from one version electric airsoft gun gearbox to another, they all use the same basic airsoft gearbox parts to function.

Electric Airsoft Gun Internals:

AEG gearbox internals

  • The Gearbox Shell – This shell houses all the internal parts and is engineered to fit into the receivers of various electric airsoft guns.
  • Airsoft Bushings and/or Airsoft Bearings fit into holes on each side of the electric airsoft gun gearbox to allow the gears to rotate smoothly.
  • Airsoft Shims go in-between the airsoft bushings and the airsoft gears to adjust gear height and reduce slop.
  • Airsoft Gears – Most electric airsoft guns use three gears, a Bevel gear which transfers the energy from the motor to the spur gear as well as keeps the gearbox for spinning back on itself by way of an anti-reversal latch.  The Spur gear is moved by the Bevel Gear and is used to turn the sector gear.  The Sector gear is responsible for moving the tappet plate back as well as pulling the piston back.
  • Anti-Reversal Latch – The anti-reversal latch is a simple piece of metal that is spring loaded to engage with the bevel gear and keep it from running backwards.
  • Airsoft Main Spring – This spring is responsible for pushing the piston forward.  Springs are nothing more than stored energy.  Airsoft springs have ratings using various systems from % to M numbers.  M stands for Meters Per Second.   Generally speaking, the higher the number the more energy the airsoft BB’s will be fired with.  Airsoft upgrade springs can be either variable, allowing a gentle pull at when the sector gear starts pulling the piston back, or a linear spring that holds the same rate through out the airsoft upgrade spring.
  • Airsoft Spring Guide – The spring guide’s job is to keep the spring centered and from flexing.  This is also what your full stock or buffer tube gets bolted to on M16 rifle style airsoft guns.
  • Airsoft Gearbox Cylinder – The cylinder is simply a chamber that the piston slams through to compress air.
  • Airsoft Cylinder Head – The Cylinder Head is usually a piece of polycarbonate or aluminum that also has a nozzle that comes off it allowing a volume of air from the larger cylinder to be compressed through the nozzle, there by propelling the BB out of the hop up chamber.
  • Airsoft Piston –  Made from a variety of materials, including metal and polycarbonate, pistons have a rack of teeth on them allowing the sector gear to pull them back after the spring slams them into the cylinder.
  • Airsoft Piston Head – The Piston head bolts to the piston and has a O-Ring on it to prevent air from getting past the piston.  The more air the piston pushes forward, the stronger the charge of air coming out the barrel will be.
  • Airsoft Tappet Plate – The Tappet plate is pulled back by a knob on the sector gear and springs forward once released.  It’s used to hold the air nozzle on the cylinder head.
  • Airsoft Air Nozzle – The air nozzle attaches to the tappet plate and slides back and forth on the nozzle sticking out of the cylinder head.  The air nozzle performs two tasks.  The first task is to slide back and forth on the cylinder head allowing one airsoft BB to ram out of the magazine into the hopup chamber.  Once done the tappet plate rams the nozzle forward into the hopup rubber creating a solid seal.  This allows transfer of all the air compressed by the piston into the cylinder head to be transfered to the back and sides of the bb, propelling it out of the barrel and down range.
  • Selector plate –  The selector plate is a piece on some gearboxes that moves forward or back when the selection switch is moved from safety to the various firing modes.
  • Trigger assembly – The trigger assembly activates a switch that transfers power from a battery to the motor there by activating the electric airsoft gun.

Putting it Together:  How a Gearbox works.

Below is an animated GIF displaying how a Version 2 electric airsoft gun gearbox works.  See if you can identify all the pieces described above!

Electric Airsoft Gun Version 2 Gearbox

 What are the Different Versions of Electric Airsoft Gun Gearboxes?

Version 1 Electric Airsoft Gun Gearbox

The Version 1 gearbox was designed by Tokyo Marui for thier FAMAS line of airsoft guns.  The motor is mounted directly in the shell.

version 1 electric airsoft gun gearbox exterrior version 1 electric airsoft gun internals

Version 2 Electric Airsoft Gun Gearbox

The Version 2 gearbox is probably the most mass produced in the world and fits in a variety of guns based on the M16 airsoft rifles, MP5 and G3 series airsoft guns.  The original designs were prone to breakages, especially when cold weather makes the metal cold, of the gear box shell itself.   Reinforced gearboxes have helped with this issue somewhat, but it’s still common to break the front of the gearbox in cold weather with high powered, upgraded airsoft springs.  The motors are mounted in the grip of the airsoft guns, not mounted to the gearbox like a Version 1.

version 2 electric airsoft gun gearboxversion 2 gearbox internals


Extended V2 Electric Airsoft Gun Gearbox

Extended V2 AEG Gearbox

Content for this section mostly credited to Age:

Extended V2. Used in the CA and A&K SR25 electric airsoft guns. The upper portion of the airsoft gearbox, including the piston and cylinder assembly is extended. The G&G SR25 uses a normal length V2, and to make up for the the lost space all they did was extend the hop up unit and air nozzle. G&P has a few different versions of SR25’s, some use the extended gearbox like the CA/A&K, while other G&P models use the extended air nozzle/hopup like the G&G. The Echo1/JG SR25 uses an extended shell, but normal V2 inners with an extended cylinder head to push the piston back far enough to use normal gears and other components.

Version 3 Electric Airsoft Gun Gearboxes

Tokyo Marui’s 3rd design is the aptly named Version 3 electric airsoft gun gearbox.  Version 3 gearboxes lack don’t tend to shatter in the winter and as such tend to get used more often in the cold.  You’ll find version 3 gearboxes in AK series airsoft guns, along with the MP5K, UMP, AUG and G36 airsoft guns.  They’re also used in SIG airsoft gun replica’s but, those version 3 gearboxes have the motor separate from the gearbox.  Normal Version 3 gearboxes have a cage built in to house the motor.

Version 3 Electric Airsoft Gun gearboxVersion 3 gearbox internals


Version 4 Electric Airsoft Gun Gearboxes

The Version 4  electric airsoft gun gearbox was a one off design purpose built for the Tokyo Marui PSG-1 airsoft sniper rifle.  To my knowledge that’s the only gun that ever used it.  Sadly, I’ve not seen a PSG-1 since 2007 when a friend of mine sold his before deploying.  Age has graciously provided pictures of the V4’s internals.

Version 4 PSG-1 Airsoft Sniper Rifle GearboxVersion 4 PSG-1 InternalsVersion 4 PSG-1 Internals

Version 5 Electric Airsoft Gun Gearboxes

Yet another Tokyo Marui one off design.  Version 5 electric airsoft gun gearboxes are only utilized in their replica of the UZI Submachine gun.  I’ve personally NEVER seen one of these in my life.  Once again, because it’s such a specialized gun/gearbox, very few are floating around, Age, has once again assisted in providing AEG Gearbox pictures for the TM Uzi. TM Uzi, Version 5 AEG GearboxTM Uzi, Version 5 AEG Gearbox


Version 6 Electric Airsoft Gun Gearboxes

Version 6 electric airsoft gun gearboxes are used for the Thompson line of AEG Submachine guns as well as P90’s.  The wiring and switch is clamped down to the exterior of the gearbox.  Some parts like pistons and spring guides can be used from other designs like the V2 and V3.  Other internal parts like one set of bushings are proprietary.

Version 6 AEG GearboxVersion 6 AEG Gearbox internals

Version 7 Electric Airsoft Gun Gearbox

The Version 7 Electric Airsoft Gun Gearbox is used for the M14 rifle series of electric airsoft guns.  These also suffer from the same cracking issues Version 2 AEG gearboxes are prone to.  The electrical components are all externally mounted to the gearbox. They require specific parts to replace the cylinders, and gears due to length and diameter differences between them and other gearboxes.

Version 7 Gearbox M14 airsoft rifleVersion 7 AEG Gearbox internals

Version 8 Electric Airsoft Gun Gearbox

One more one off model of electric airsoft gun gearbox is the Version 8.  This is only used  in the Tokyo Marui Type 89 airsoft rifle.    It has a gear operated burst option built into it and internally looks very similar to a Version 2 electric airsoft gun gearbox.

Version 8 AEG GearboxVersion 8 AEG Gearbox internals

SAW and M60 Electric Airsoft Gun Gearboxes

These are fairly common as well, especially with the prices of SAW’s dropping down into reasonable territory.  Once again, pictures are courtesy of Age.

CA/A&K/Echo1 M249 AEG Gearbox

Zoom in (real dimensions: 600 x 216)SAW AEG GearboxSAW AEG Internals

A&K M60 Gearbox

Zoom in (real dimensions: 600 x 450)A&K M60 AEG GearboxZoom in (real dimensions: 600 x 450)A&K M60 AEG Gearbox internals

Zoom in (real dimensions: 800 x 600)

Variations, Other Gearboxes

The above electric airsoft gun gearboxes are the ones most often used, and were all designed by Tokyo Marui.  Other company’s such as ICS, Classic Army, STAR and Ares have put out gearboxes that only fit in specific model airsoft guns.  Some are simply modified version twos, others are beefy and designed to run hard like those made for SAW’s.   Either way, this guide is a good recap for those of you wanting to know about the gearbox of your electric airsoft gun.







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