Version 2 / M4 Gearbox Guide

Intro

In this guide, you will become familiar with version 2 gearboxes.  This will give you more confidence when upgrading your gun or doing general work inside of the gearbox. 

                         

1. Parts

– Gearbox Shell:  This shell houses all the internal parts and is engineered to fit into the receivers of various electric airsoft guns.

– Bushings and/or Bearings:  These fit into holes on each side of the electric airsoft gun gearbox to allow the gears to rotate smoothly.

– Shims: These go in-between the airsoft bushings and the airsoft gears to adjust gear height and reduce slop.

– Motor:  The motor converts electrical energy from your battery and turns it into mechanical energy which is used to spin the gears.

– 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.

– Main Spring:  This spring is responsible for pushing the piston forward.  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.

– 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.

– Gearbox Cylinder:  The cylinder is simply a chamber that the piston slams through to compress air.

– 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.

– 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.

– 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.

– 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.

– 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:  The trigger assembly activates a switch that transfers power from a battery to the motor there by activating the electric airsoft gun.

2.  Operation

The animation below demonstrates how this gearbox operates.

3. Disassembly and Assembly – (I’ll upload my own video soon)