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Airsoft V2 Gearbox Guide


Let us start by saying that gearboxes can be hard work to troubleshoot and maintain. Here, our goal is to make it a little bit easier for people to understand the inner-workings of the gearbox and how to diagnose problems you may be facing with your V2 gearbox.

How a Gearbox Works

Understanding what you’re working with is always a good idea before tampering with your gearbox. Here is a good animation displaying the inner workings of a gearbox, and how they work together

In simple terms, a standard airsoft AEG uses a battery to power a motor that turns gears in order to compress a spring and fire a BB.

Note - It is recommended that you watch ALL the videos provided before attempting anything mentioned. As there is only so much one can convey in words, the videos will provide you with a visual aid and a fuller understanding of the concepts mentioned in this guide.


Part Names and Functions

Gears, Bearings & Delay Chips

In a gearbox, gears are one of the most important pieces, and also one of the most prone to breaking. They are “the heart” of the gearbox. Each gear works to perform a separate job in order to keep the gearbox functioning correctly. There are four main gears, the Pinion gear, the Bevel gear, the Spur gear, and the Sector gear. Pinion Gear- The Pinion gear is the gear attached to the motor armature (the exposed spinney part), and the first gear in our line-up. The Pinion spins on a plane perpendicular to all the other gears, and therefore is the most at risk for energy loss.

  1. Anti-Reversal Latch The Anti-Reversal Latch, or ARL, is used to keep the gears from turning in reverse. It will lock up the gearbox if the gears spin backwards and should be double checked when installing, to ensure it is positioned properly.

  2. Bevel Gear The bevel gear is angled, so it can sit tightly with the pinion gear, to transfer energy from the motor to the other gears.

  3. Spur Gear The Spur or “step” gear is the gear that sits between the sector and bevel gear. It is used to transfer energy to the sector gear.

  4. Sector Gear The sector gear pulls the piston back and release it and comes with a small peg on it to engage the tappet plate to feed BB’s. There are two main kinds of sector gears.

    1. Single Sector Gear An SSG has one set of teeth on one side of the gear, to pull the piston back. SSG's are the standard in most AEG weapons.

    2. Dual Sector Gear A DSG has two separate sets of teeth on each side of the gear, allowing for a must faster rate of fire.

  5. Spring Guide Holds the main spring to ensure it does not shift position.

  6. Spring A strong spring that determines the desired energy output of your AEG.

  7. Piston The piston is forced forward by the spring into the cylinder, forcing air out of the nozzle to fire BB's.

  8. Cylinder A cylindrical tube that holds compressed air.

  9. Cylinder Head Sits between the cylinder and air nozzle and adds strength and stability.

  10. Air Nozzle Sits at the end of the cylinder head to guide and launch the BB down the barrel.

  11. Tappet Plate The Tappet plate holds the air nozzle up to the cylinder head and is moved backwards by the peg on the sector gear, the tappet spring then pulls it forwards. Selector Plate- Engages the cut-off lever and safety lever, allowing for safe, semi-auto, and full auto firing modes.

  12. Tappet Return Spring The spring that pulls the tappet plate back into position after each cycle of the sector gear.

  13. Battery Wire Connector This wire usually travels through to the front handguard or stock of the gun where the battery is stored.

  14. Switch Assembly The switch assembly engaged when two metal contacts provide energy for the motor to spin and cycle the gearbox and fire the weapon.

  15. Trigger The lever which you pull to cycle the gun and fire BB's.

  16. Motor (with pinion gear attached) Usually located inside the pistol grip, the motor is the most important component in the gearbox. Used to turn the gears, the motor is central to proper function. When selecting gears, make sure to get a motor that complements the gears.

Bushings Thick washers, made of metal that go inside the gearbox shell to space the gears and prevent them from wiggling when turning.

Bearings More efficient but can be more fragile than bushings, bearings can offer higher efficiency due to their reduced friction between the gear axle and gearbox shell.


Upgrades and Recommended Products

  1. Gears Budget: SHS (but QC is not that great and you need to be careful) Best: ZC Leopard or Phoenix

  2. Motor The kind of motor you should be looking for NEO or “NSFB”, as ferrite motors are now obsolete. We do not recommend going down the budget route for these as they never last long. The best brands going are Option No.1, Tokyo Marui, ASG Infinity and Lonex

  3. Spring Guarder (SP), Prometheus (M), ASG (M) Avoid coated springs as eventually the coating comes off.

  4. Bushings/Bearings Budget: Stock, FLT bushings, SHS bearings/bushings Best: NSK bearings, FLT bushing

  5. Tappet Plate Retro Arms CN

  6. Anti-Reversal Latch Lonex

  7. Piston You're looking for a steel-tooth rack to ensure strength and reliability. Make sure to superglue the piston rack in so as to prevent it from kicking out from the piston body during use

  8. Shims Most steel shims work fine(example: SHS)

  9. Air Nozzle Budget: Stock Best: Lonex, SHS, GATE

  10. Cylinder Head Lonex, SHS, DCI, GATE

  11. Piston Head Lonex POM (Don’t buy mushroom piston heads, they’re a gimmick and offer no real benefit)

  12. Cylinder Any non-ported brass or steel cylinder will work, so long as they polish and provide a good air seal. Avoid aluminium as they do not polish and can get marred easily

  13. AOE Correction Chemical resistant, hard sorbothane or polyurethane.

  14. Gearbox Shell Budget: Stock, VFC, G&P, Krytac, Specna Orion, ICS, Lonex Best: EON V2 Gearbox rev. 2 [CNC] - Titanium, Retro Arms CNC

  15. MOSFET Budget: Jefftron Mosfet 2, GATE NanoASR. Best: GATE Titan Advanced

  16. Lubricant Superlube

  17. Batteries Budget: Any shop's own brand Best: Tokyo Marui, Option No. 1


Good practice and habits


A shim is a thin piece of metal resembling a washer, which is placed onto the axle of a gear. The purpose of shimming is to eliminate any unwanted vertical movement of the gears and to minimize friction between them. When done correctly, proper shimming results in a quieter, more efficient, and more reliable Automatic Electric Gun (AEG). I will guide you through the steps of effectively shimming your AEG and provide links to instructional videos for reference. Note: While some individuals shim the Spur gear to the Bevel gear, it's recommended to always prioritize shimming the Pinion gear to the Bevel gear. This ensures that the motor height and the meshing between the Pinion and Bevel gears remain accurate. Keep in mind that each gearbox may vary, requiring a different number of shims and level of work.

The initial step in the shimming process involves dismantling the gearbox completely (refer to part 5 for guidance). Once all components have been removed, you will be left with the gearbox shell. Ensure that the gearbox shell is clean. At this stage, securely attach your bushings or bearings using superglue, ensuring they are perfectly flush within the gearbox. This step is crucial, as proper shimming outcomes cannot be achieved without it. Insert only the gears into the gearbox, fasten them with screws, and observe any vertical movement in the gears. Rotate the gears and take note of any scraping or rubbing sounds they produce.

Adjust the motor height appropriately and shim the bottom side of the Bevel gear. The optimal way to adjust the motor height is through visual assessment. Place only the Bevel gear into the right section of the gearbox shell, position the motor into the grip, and manually fine-tune the motor height until it meshes seamlessly with the Bevel gear. You might need to add shims beneath the Bevel gear to ensure proper alignment with the Pinion gear (refer to the 12:30 mark in video 1). Following this, shim the top side of the Bevel gear. Ideally, there should be minimal play, approximately 0.1mm, both vertically and laterally. Assemble the gearbox shell with just the Bevel gear inside, and fasten it with screws. Attach the pistol grip with the motor and observe the meshing between the Pinion and Bevel gears. Aim for symmetrical alignment between the Pinion gear and the Bevel gear. You can gauge gear play using a small screwdriver by attempting to move the gear in various directions. Remove the pistol grip and test the gear's free spinning. If it doesn't spin freely, decrease the shims on the top side. It's crucial not to remove shims from the bottom, as that would compromise the meticulous work on motor height and meshing. Keep all shims in place within the gearbox after shimming to maintain proper meshing.

Proceed to shim the bottom side of the Spur gear. Position your gears within the left section of the gearbox shell. Observe the gap between the Bevel and Spur gears, aiming to minimize this gap without causing direct contact or rubbing between the gear faces. Add shims beneath the Spur gear until the optimal balance is achieved. The goal is to maximize gear teeth contact for efficient energy transfer and meshing.

Shim the top side of the Spur gear. Test the vertical movement of the Spur gear by gently pushing up on the gear axle. Add the appropriate number of shims to the top side and close the gearbox shell. Repeat this process until you achieve approximately 0.1mm of movement. Once again, assess the free spin of the gears and adjust shims as needed.

Next, proceed to shim the bottom side of the Sector gear. By now, you might have a rough estimate of how many shims are needed for the bottom side. Observe how the Sector gear rests atop the gear face of the Spur gear. Add enough shims to slightly elevate the Sector gear to prevent direct contact between the gear faces.

Shim the top side of the Sector gear. Add or remove shims until you attain about 0.1mm of vertical movement. Test the movement of all gears when they are together within the gearbox. Fasten the gearbox with screws and rotate the gears. When done accurately, there should be minimal resistance between the gears, and they should rotate smoothly. If you detect any rubbing or squeaking sounds, inspect the positioning and alignment of the gears.

Perform an integrated test. Pay attention to the sounds generated by the gearbox during firing. You should notice a significant reduction in noise, resulting in a cleaner sound. Note: This overview provides a simplified explanation of shimming. Achieving precise shimming requires substantial trial and error. The most effective approach is hands-on learning through video tutorials.

Cleaning & Lubricating

When opening up your gun for the first time, you’ll want to clean out the stock lube. Stock lube is often low-quality, cheap, sticky residue that will gum up your gears. Take everything apart, clean the bushings/bearings, gears, gearbox shell, and anything else that may have stock lube on it. Clean using rubbing alcohol, paper towels, and a toothbrush to scrub it all off. Once dry, use Super lube to grease the gears, piston track, tappet track, and gear axles. Use a very small amount of lube on the inside of the cylinder. Do not over lube.

AOE - Angle of Engagement

AOE is the area in which the first tooth of the Sector gear contacts the first tooth(Pick up tooth) of the piston. Oftentimes, this will need correcting in stock guns. If you find that your Sector gear is contacting the second to last tooth instead of the pick up tooth of the piston, you will need to correct this by adding a sorbothane (anti-vibration) pad to your cylinder head then shaving off one or more teeth from your piston from the pickup end if needed, so that initial contact between the sector and piston pickup teeth is parallel (do not take off the pickup tooth). This is done to eliminate “rolling contact” between the sector and piston teeth, to enhance durability of both.

Air seal & Compression

Sealing and compression go hand in hand. To check the compression, take the piston, cylinder and head. Quickly push the piston into the cylinder, covering the hole in the front of the cylinder head. If you feel resistance and can't push the piston any further, the compression is good. If the piston has little or no drag, then there is a leak or poor compression and the cause needs to be determined, possibly requiring new parts.


To radius a gearbox means to take material off of the corners of the gearbox shell cylinder window in order to strengthen the gearbox and prevent cracking by spreading the force exerted by the piston around the corners of the window. To radius a gearbox, first locate your “steps”. A step is any sharp corner in the cylinder window. To eliminate these sharp corners use a metal file or Dremel.

Note- This does not have to be an immediate modification, but is a good practice. However, due to G&G gearboxes being composed of a high zinc-content alloy, radiusing is a highly recommended modification to extend the life of this weak gearbox shell.


Meshing is how your gears interact and transfer energy to one another. The better the meshing, the more efficient the transfer, and quieter the gears. Gear shape matters significantly for proper meshing. For example; some gears such as a ZCI 9T or SHS10T bevel can mesh well with Siegetek spur gears, where some gears will not mesh well when put together. An example of this would be an ASG motor pinion gear and an SHS bevel gear.


Typically, stock wiring isn’t ideal. It is recommended to change wiring to a solid core 16 gauge copper wire to allow for faster transfer of energy. When changing wiring, Deans connectors are always preferred over Tamiya because of the lesser resistance offered by deans connectors.

Short Stroking

Short stroking is the process of removing gear teeth and (optionally) piston rack teeth, and is usually done in conjunction with using a heavier spring. This is traditionally done to reduce cycle times, or correct overspin if needed. This process is often done using a Dremel to remove around 2-3 of the back teeth from the Sector gear most of the time (or half of the entire piston rack when using a DSG). By doing this, you reduce your FPS as the spring is not as compressed, so you will also need to use a heavier spring to compensate. What this does is it reduces the return time of the piston to the cylinder head, therefore reducing the chance of PME. A general rule of thumb is for every tooth you remove, you will lose ~15 FPS and will need to use an appropriate spring to compensate.

PME Correction

This can be done to reduce or eliminate the risk of "PME". This is a premature engagement that occurs when the gears shift too quickly and the piston pinion teeth engage before they fully return into the cylinder head. Premature engagement can destroy the gear sector and piston rod teeth, thus damaging the AEG replica. PME correction can be done in a number of ways including: reducing the piston, using a stronger spring, slowing down the cycle relative to the gear ratio or motor speed, or (not recommended) MOSFETs with active braking.


There is a certain ratio of the air volume of your cylinder and the air volume of your barrel. A simple, typically agreed upon ideal cylinder : barrel volume ratio is around 2:1, with the ratio being even higher when you use heavier BBs. When your ratio is too low, you will experience a loss in joules. Under-voluming (a ratio of <1:1) often happens with stock guns when using heavier BBs (Imagine having 400 FPS with .20g BBs (1.49j) and then putting .32g BBs in and getting 280 FPS (1.17j).). You experience a loss in energy from using heavier BBs, usually due to manufacturers using improper parts to promote proper voluming such as: Bad air seal, ported cylinders, and unnecessarily long inner barrels.



There are plenty of YouTube tutorials out there on how to remove the gearbox from your AEG, but I'll describe the general process:

For most AEGs, you simply remove the latch from the body, slide the receiver over the top. Remove the magnetic trigger screw and the spacer tube. , disconnect the wire from the motor, remove the gun stock, remove the latch just above the trigger, and remove the gearbox.

Gather the right tools needed for the job. All in all, the IFixit suite contains everything you need. If your piston is not in the resting position, activate the ARL by inserting a small screwdriver into the bottom of the gearbox and pulling the ARL out. Remove the gearbox screws.

Insert a screwdriver into the spring guide hole to prevent the spring guide from falling out. Remember to keep the cylinder down while doing this and carefully remove the top half of the gearbox housing. Once removed, reduce the spring tension by removing the spring guide with a screwdriver. If your transmission has a quick-change spring system, insert the correct key and turn until the spring guides to the rear.

Remove the tappet spring plate located at the front of the transmission and remove the cylinder/piston assembly.Remove the gears, starting with the bevel, then the arc, then the spur. This order is not particularly important. Unless you are redoing the shims, make sure to keep the shims in the correct gear.

Remove ARL and enable. The trigger has a small spring that fits snugly into a slot in the gearbox, don't lose this spring. The ARL also has a very small spring that can fall out, don't lose it.

Remove the safety lever. This lever also has a small spring that should not be lost. The safety lever is located just in front of the trigger. If the rings are not glued, remove them. Remove the power cord/wire assembly from the trigger. Remove the assembly tension spring, then remove the screws securing it.

Remove the cutting lever by loosening the screw securing it. Remove the pick plate. First remove the spring from the pick plate, then slide the plate out.



Now that you have your AEG disassembled, how in the world are you going to reassemble it? Again, I will walk you through the steps required to reassemble your AEG.

  1. Install the selector plate. Make sure it fits well inside it’s tracks and moves freely.

  2. Install the cut-off lever and attach the spring that goes between the selector plate a cut-off lever.

  3. Install the wire/trigger harness and screw it in. Install the tensioning spring. 4. Make sure the wires fit in the correct tracks in the gearbox

  4. Install the safety lever, making sure to tension it with its spring. It should move freely.

Install the rings/bearings. These should be glued to the gearbox housing but not necessary. Install the gears. Start with the promotion and the area. Now install the ARL, fully tension it and install the bevel gear.If done correctly, this will prevent the bevel from turning clockwise. If it is anywhere between the spike and the bevel, the position is incorrect. The ARL is a bit difficult to set and sometimes pops out of the transmission. A useful trick to keep it in place is to use a strong magnet located under the gearbox.

Place the cylinder head into the cylinder, the air nozzle inside the tappet plate, then slide the air nozzle onto the cylinder head. Place the piston inside the cylinder. Place the assembly in the gearbox making sure the holes in the cylinder head align with the gearbox housing. Place the tappet plate spring back into the gearbox. Air nozzle and ejector plate must move together. Make sure the piston moves inside the groove of the gearbox housing.

Activate settings. It can be a bit difficult because of spring. You can use some glue to keep the spring attached to the trigger if needed. This is the hardest part of all. Install springs and spring guides.Place the screwdriver inside the spring guide and push inward until the spring guide is in the groove inside the gearbox. Remember to keep the cylinder down while you do this or it will pop out.

Position the top half of the gearbox. Without force, make sure each cylinder fits snugly against the top half of the gearbox. If the transmission seems to bounce back to its original position but not quite correctly, regularly pushing the tap in or pushing the spring guide a little will help the transmission close completely.Screw into the gearbox, check that the piston is on its rails, the air nozzle moves freely, there are no wires entangled, the gears are not too tight, etc. Reinsert the

transmission into the AEG. Make sure not to reverse the polarity of the leads to the motor.


Things/Products to Avoid

Plastic Piston Tooth Racks These will wear out very fast and should be replaced with full metal rack pistons as soon as possible.

Plastic Spring Guides Replace these with a metal and preferably ball bearing spring guide.

Plastic/brass Bushings, Gears, ARLs, and Cut-off Levers Should be good metal (quality steel, 7075, chromoly, etc) Clear nylon air nozzles: Not only ugly, but prone to breaking/cracking

Over-Lubricating Your gears and O-Rings don’t need to be caked in lube. Low TPA Motors: Motors under 16 TPA are inefficient. They are often labelled as “high speed” as they will have a greater maximum RPM compared to higher TPA motors. A low TPA motor is often paired with high ratio gears, this is inferior to a high TPA motor and low ratio gears in semi-auto focused builds as shown by the larger amount of power it draws from the battery, the heat produced, and the acceleration time of the motor.

Brands to Avoid From the repairs and inspections we have done on airsoft weapons. The following brands fall short of quality and reliability.

  • Lancer Tactical

  • Angel Custom Parts

  • Some G&G parts

  • Some KWA parts

Note: Much of the information here will apply to other gearbox types with only marginal differences between each type.

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