Airsoft Gearboxes

If your M4 needs a revamp, a new gearbox is the easiest way to do it. The Delta Armory Complete Version 2 Gearbox for M4/AR-15 AEG is compatible with almost every M4/AR-15 AEG on the market and is well-equipped with reinforced parts straight out of the gate.

This is the same gearbox used in the Delta Armory CHARLIE™ line AEGs, boasting a quick change spring guide, 18:1 steel gears running on 8mm bushings, an SHS piston with a full steel tooth rack, an SHS reinforced tappet plate and a reinforced gearbox shell with radiused cylinder window corners.

The pre-installed spring will provide around 380 FPS when installed, so if you plan to use this gearbox for anything other than a semi-auto-locked DMR build you will need an M100, M105 or weaker spring to keep it within site limits. Thankfully, the quick change spring system makes spring swaps a breeze! Whether you are breathing new life into an old M4 AEG or you are building an AEG from scratch, this complete gearbox will save you loads of time and messing around!

If you're looking for the cheapest and easiest way to convert your M4/AR-15 AEG to HPA, you just found it! The Ares Drop-in HPA Engine Conversion Set for M4/AR-15 V2 Gearbox is a complete set with a V2 gearbox shell, HPA engine and EFCS module all pre-built, saving you hassle sourcing the right parts while saving you a few quid as a bonus!

This HPA Engine Gearbox is designed as a drop-in replacement for standard M4/AR-15 AEG Version 2 gearboxes but it may need alignment and tuning to fit certain receivers and HOP-up units. To power the pre-installed EFCS, an 11.1V LiPo battery with a Deans battery connector is required and the air line fitting is US spec, meaning it will only accept US-type air lines and won't work with EU-type lines. For those as yet uninitiated future HPA players; this set does not include an air line, regulator or air bottle and you will need these to get into the HPA game!

This is the semi/full auto version designed for non-ambidextrous M4/AR-15 AEG receivers and is equipped with a standard M4/AR-15 curved trigger, ideal for almost any build style. As with any internal upgrade, this engine will require expertise to install and some level of familiarity with M4/AR-15 AEG internals. If you're struggling, you can contact us or your local Airsoft tech for advice.

The Spenca CORE™ V2 Gearbox Shell provides 8mm bushings, radiused cylinder windows to help prevent cracks, and quick release spring functionality. Perfect for starting your ultimate gearbox build!

If you've decided to join the dark side and HPA your M4, this set will sort you out! The Storm Airsoft HP-R Storm System HPA Engine is a complete drop-in conversion kit for rear-wired version 2 gearboxes, packaged with everything you need to convert your AEG, bar the usual HPA regulator, airline and hose.

The included FCU offers a wide range of adjustable parameters, including programmable fire modes, rate of fire adjustment, and nozzle dwell time adjustment, ensuring reliable feeding with every shot. While it is a drop-in kit, this set will require a certain amount of familiarity with AEG internals and HPA. Luckily, Storm Airsoft provides a useful installation video which makes the process even easier.

Benefits of running HPA over a standard AEG gearbox include minimal FPS deviation between shots for improved accuracy, near-instantaneous trigger response for cranking out those double taps and a wide range of tuning options and adjustments, perfect for casual skirmishers looking to take their build to the next level. If you want the competitive edge HPA provides with minimal effort, the Storm Airsoft HP-R Storm System HPA Engine is the way to go!

Whether you are upgrading your SMG-5 or repairing it, the CYMA CM.041G/CM.041H Complete Gearbox E-Edition High-Speed is a great excuse to do both at the same time! This gearbox is a Version 2, designed for CYMA CM.041 series SMG-5 AEGs but should fit most SMG-5 AEGs on the market (not SMG-5K) and also includes a high-speed motor of the long shaft variety.

As the heart of the CYMA E-Edition High-Speed Platinum AEG series, this gearbox is absolutely packed with upgraded parts. Highlights of the internals include the CYMA MOSFET/ETU system, steel high-speed 13:1 ratio gears, an aluminium silent piston head and cylinder head and a quick change spring system. Being a replacement original parts set, this gearbox is the exact setup found in the superb CM.041G and CM.041H AEGs, meaning if you have ever been envious of their performance you can now make your SMG-5 shoot just as nicely!

If you've encountered issues with your Specna Arms PRIME™ M4/AR-15 AEG's gearbox, you're in luck! This replacement gearbox shell is an original replacement part, allowing you to revive your AEG back to good health. It comes with the J-Cage bearings pre-installed, meaning it is unlikely to be compatible with other AEGs.

This reinforced Gearbox has an anti-reversal release window, pre-cocking and AoE inspection windows, reinforcements in high-stress areas, a motor gear inspection window, a trigger adjustment function and screw holes allowing for easy alignment. Get a quick fix for your PRIME™ AEG with the Specna Arms Aether™ V2 Gearbox Shell w/ J-Cage Bearings!

If you're planning the move over to HPA to take your build to the next level, the PolarStar Airsoft JACK™ HPA Engine Conversion Kit is a great way to do it! A drop in cylinder replacement single-solenoid HPA conversion kit, the JACK™ is available to fit either version 2 (M4/AR-15) or version 3 (AK-47/74) gearboxes, including everything you need other than your airline, regulator, air bottle and FCU battery.

Capable of a stunning 30 rounds per second in most setups, with more air volume and a wider range of velocity adjustment than its rivals, the JACK™ is highly efficient with a stunning response rate and a vast range of programmable customisation options built into the included fire control unit (FCU). If you're a performance seeker, the PolarStar Airsoft JACK™ HPA Engine Conversion Kit will change your game!

If you're planning the move over to HPA to take your build to the next level, the PolarStar Airsoft JACK™ HPA Engine Conversion Kit is a great way to do it! A drop in cylinder replacement single-solenoid HPA conversion kit, the JACK™ is available to fit either version 2 (M4/AR-15) or version 3 (AK-47/74) gearboxes, including everything you need other than your airline, regulator, air bottle and FCU battery.

Capable of a stunning 30 rounds per second in most setups, with more air volume and a wider range of velocity adjustment than its rivals, the JACK™ is highly efficient with a stunning response rate and a vast range of programmable customisation options built into the included fire control unit (FCU). If you're a performance seeker, the PolarStar Airsoft JACK™ HPA Engine Conversion Kit will change your game!

Ideal for reviving worn out RIFs or as a backup for a rainy day, this is a complete and assembled gearbox including motor, that is ready to drop into any compatible Version 2 accepting replica.

If you love working on gearboxes or have a version 3 custom build on the cards, the FPS Softair Complete Gearbox Spring Set for V3 Gearbox belongs in your toolbox. This set includes all of the springs needed for a version 3 gearbox build, including the tappet plate spring, ARL spring, motor height spring, cut-off lever spring, trigger return spring and switch return spring.

All of the springs in this set have been manufactured by FPS Softair to be more durable than the original springs and with more precisely calculated tension for maximum efficiency. Whether you've lost a spring, are working on a version 3 gearbox build or need spares for your technical projects, the FPS Softair Complete Gearbox Spring Set for V3 Gearbox will be useful addition to your parts bin!

Specna's ORION™ reinforced gearbox has gained an excellent reputation since it was released installed in the EDGE™ series of AEGs, and now Specna are offering you the opportunity to create your next gearbox build with a solid, reliable shell to tie it all together. Rated to handle heavy springs and including enhancements such as radiused cylinder windows and quick change spring functionality, the ORION™ gearbox shell is probably a tad more affordable than it should be!

If you're done with AEGs and want to revamp your build for HPA, the GATE PULSAR D Dual Solenoid HPA Engine is a fantastic option. Designed for Version 2 AEG gearboxes, the PULSAR D is designed to work with a GATE TITAN™ II V2 ETU (HPA Version), giving you unlimited advanced programming options along with the bob on consistency, top-tier accuracy, killer rate of fire and wealth of tuning opportunities HPA builds are known to provide.

The set includes the complete engine but will require a V2 gearbox shell, V2 trigger and TITAN™ II ETU HPA Version to complete the build. When compared to the original and more affordable PULSAR S, the PULSAR D offers a higher FPS range, universal compatibility with AEG nozzles, less precision required in the assembly of the build and impressively high air efficiency, using only 0.7 PSI per shot on average at 90 PSI with a 0.8L air tank.

The PULSAR D also has the edge in accuracy and versatility over the simpler single solenoid PULSAR S, being suitable for any build objective, from CQB monster to DMR dominator. As with all internal upgrades, we only recommend this engine to those who are confident working on AEG and HPA internals, but if you're ready for the PULSAR D, you're sure to be impressed!

A complete V6 gearbox designed as a replacement for CYMA P90 AEGs to breathe new life into your weapon.

A pre-assembled, ready to use complete gearbox set designed for use in 6mm Airsoft BB replica M14 AEGs. With all the components assembled and in place, this gearbox is ready to be dropped into place in your M14 AEG, replacing any old and worn out gearboxes.

A shell for gearbox type V2 with reinforced aluminium construction. The front part has been strengthened with the most exposed area being considerably thickened and the area of the contact with the cylinder has been improved so as to evenly transfer the loads.

The shell is mounted using its 8mm bearings. This gearbox shell is designed for use in J.G replicas but should potentially work in replicas of other makes and manufacturers.

If you're after HPA performance with professional-level tuning options, the PolarStar Airsoft F2™ HPA Engine Conversion Kit is the way to go! An updated version of PolarStar's incredible Fusion™ engine, the F2™ is a dual-solenoid engine, allowing tuning of both the loading speed and air volume via the included digital FCU (fire control unit).

The set is designed to drop into either a V2 (M4/AR-15) or V3 (AK-47/74) gearbox (depending on the variant you choose), including everything you need other than your airline, regulator, air bottle and FCU battery.

Offering a variable rate of fire up to a stunning 30 rounds per second, adjustable velocity and a vast range of programmable options, including alternative fire modes, anti-stiction mode, "closed bolt" mode and "AEG" mode, the F2™ engine is the right choice for experienced HPA users looking to move up to a more complex, high-performance engine. If this sounds like you, the F2™ HPA Engine Conversion Kit belongs in your build!

If you've got an AK AEG to repair, why not take the easy route with the CYMA V3 Gearbox w/ Motor for AK-47/74 AEG; Rear Wired? This complete gearbox set is pre-built, fitted with a powerful high-torque motor and motor cage, making it practically a drop-in installation in any rear-wired AK AEG configuration. 

Inside, we are treated to 18:1 ratio steel gears running on 7mm steel bushings, a polymer piston with a robust full steel tooth rack and a quick-change spring guide for easy power tuning. Being made to the CYMA "Standard" spec, we expect this gearbox to output around 380 FPS when installed, so a reduced power spring (M90, M100 or M110) is recommended. Thankfully, the quick-change spring system makes spring swaps a piece of cake!

If your AK AEG has died and you're not sure why, a complete gearbox is the shortcut to fixing it for those who don't fancy messing around with complex AEG gearbox internals. If you'd rather spend your time shooting your AEG than tuning and repairing it, the CYMA V3 Gearbox w/ Motor for AK-47/74 AEG; Rear Wired is your ideal repair solution!

Whether you're building an AK from scratch or you need a refurb, the Specna Arms Reinforced V3 Gearbox Shell w/ Micro-Contact is ideal. Made from alloy and finished in metallic blue, this V3 gearbox shell is pre-fitted with an AK trigger, micro-switch trigger contacts, a mini-Tamiya connector and all the necessary wiring. 

Compatibility-wise, this is designed for most AK AEGs, but the shell alone can also be used in other V3 gearbox-compatible AEGs (AUG, SG55x, & AR36), provided you remove the trigger and other AK-specific parts. The set also includes a quick-change spring guide, allowing you to tune power easily without opening the gearbox itself. 

The bushing ports are 8mm in diameter, so when choosing bearings/bushings, go for 8mm examples. If you need a cheap replacement gearbox shell for a refurb or scratch build, the Specna Arms Reinforced V3 Gearbox Shell w/ Micro-Contact is a fine choice!

If you're working on a high-speed or high FPS build, the Delta Armory Version 2 CNC 8mm QSC Gearbox Shell will save you a lot of heartache in the long run! This ultra-strong version 2 gearbox shell is CNC machined from the best aluminium around, known as 7075 T651. This means if you're running a super strong spring or going for a dual-sector gear build, this gearbox shell has what it takes to keep running in the long term, being considerably stronger than standard alloy gearbox shells.

The QSC Gearbox shell also features radiused cylinder window corners to better distribute force and is pre-cut for Gate TITAN/ASTER, Perun Hybrid or Delta Armory ETU MOSFET systems, meaning no need to get the Dremel out to add advanced functionality. The bearing ports are 8mm in diameter, making this the perfect host for Bolster Armouries EZO Ball Bearing Bushings. If you're reaching for the stars when it comes to performance and want your build to last more than a few bursts, the Delta Armory Version 2 CNC 8mm QSC Gearbox Shell is what you need!

If you are looking for a high end gearbox shell to start your ultimate AEG build, stop looking, you found the best there is! The Gate EON gearbox shell is CNC machined from 7075 aluminium for a strong and lightweight gearbox with a plethora of small enhancements that make this gearbox a dream to put together.

The cylinder window is radiused on all corners and the shell has some significant reinforcements at the front end, and along the top spine. The internal wire routing has been redesigned for ease of installation, and the shell is perforated with several inspection windows so you can set your angle of engagement, adjust your pre-cocking settings and shim your gears perfectly. Is this the ultimate Airsoft gearbox? Well, it will be, once you've built it!

If you are looking for a high end gearbox shell to start your ultimate AEG build, stop looking, you found the best there is! The Gate EON gearbox shell is CNC machined from 7075 aluminium for a strong and lightweight gearbox with a plethora of small enhancements that make this gearbox a dream to put together.

The cylinder window is radiused on all corners and the shell has some significant reinforcements at the front end, and along the top spine. The internal wire routing has been redesigned for ease of installation, and the shell is perforated with several inspection windows so you can set your angle of engagement, adjust your pre-cocking settings and shim your gears perfectly. Is this the ultimate Airsoft gearbox? Well, it will be, once you've built it!

Building a gearbox from scratch? You'll need a shell to get started! The ARCTURUS Version 3 Alloy Gearbox Shell is a reinforced design with a radiused cylinder window, additional material surrounding the cylinder for extra strength and 8mm bearing holes. The rear of the gearbox is also cut for a quick change spring guide.

The version 3 shell is common to AK, AUG, AR36 and SMG-5K AEGs (not the regular SMG-5, though) so if you need a gearbox shell for any of these platforms this one will be compatible in most cases.

The EMG x CYMA Platinum Complete Version 2 Gearbox w/ Kestral Basic ETU is a ready-to-install internal upgrade built for players who want strong trigger response and reliability without the hassle of building a gearbox from scratch. Pre-assembled at the factory, it offers consistent quality control and component alignment that DIY builds can struggle to match.

Inside, you get short-stroked 13:1 SHS steel gears, an 8mm reinforced shell, and a pre-installed E-Shooter Kestrel Basic MOSFET. This setup delivers fast cycling, improved electrical efficiency, and dependable longevity, making it ideal for performance-focused skirmish builds or as a premium replacement gearbox.

This is a high-performance gearbox aimed at intermediate to advanced players or anyone upgrading from stock internals. The quick-change spring system allows rapid power adjustment without full disassembly, while silver-coated low-resistance wiring improves electrical flow and battery efficiency. Compatibility with standard Tokyo Marui spec Version 2 parts means future upgrades and maintenance remain straightforward.

If you are building a version 3 AR36 gearbox or you have an old AR36 AEG that needs a refit, this spring set will be useful! The set includes all the springs needed to complete a version 3 gearbox for AR36 AEGs except for the mainspring (the spring that provides the power). Maybe you have lost a spring, or your tappet spring got chewed up after a long and hard life? This spring set should give you all you need to get your AR36 doing its dirty work once again!

A complete V3 Gearbox for AK platform CYMA Airsoft AEG Guns. The gearbox is complete and ready to drop into a broken weapon.

The CYMA Sport Complete Version 2 Gearbox for M4/AR-15 AEG; Deans is a ready-built internal upgrade or replacement designed for players who want reliable performance without building a gearbox from parts. Pre-assembled at the factory, it provides consistent alignment, dependable shimming, and solid electrical efficiency straight out of the box.

Fitted with an onboard electronic trigger and low-resistance wiring, this gearbox offers improved trigger response compared to standard mechanical trigger setups. The reinforced shell, 8mm bushings, and metal spring guide make it a dependable choice for skirmish rifles needing a durable internal core.

This gearbox is best suited to players upgrading a worn or broken Version 2 gearbox or building a budget performance M4 platform. It is not a high-speed competition build, but it is a solid, reliable foundation that balances cost, durability, and practical performance. Compatibility with Tokyo Marui spec Version 2 parts means future upgrades remain easy.

The CYMA Sport Complete Version 2 Gearbox for M4/AR-15 AEG; Deans is a ready-built internal upgrade or replacement designed for players who want reliable performance without building a gearbox from parts. Pre-assembled at the factory, it provides consistent alignment, dependable shimming, and solid electrical efficiency straight out of the box.

Fitted with an onboard electronic trigger and low-resistance wiring, this gearbox offers improved trigger response compared to standard mechanical trigger setups. The reinforced shell, 8mm bushings, and metal spring guide make it a dependable choice for skirmish rifles needing a durable internal core.

This gearbox is best suited to players upgrading a worn or broken Version 2 gearbox or building a budget performance M4 platform. It is not a high-speed competition build, but it is a solid, reliable foundation that balances cost, durability, and practical performance. Compatibility with Tokyo Marui spec Version 2 parts means future upgrades remain easy.

This SR25 Gearbox set by CYMA is designed to fit right into most SR25 / AR25 / AR10 style Airsoft Rifles / Guns. Included is a Piston, Cylinder, Gear Set, Tappet Plate, Nozzle. This GEARBOX set does not come with the shell, internals only.

If you're looking for a cheap and easy way to get your SMG-5/MP5 AEG back up and running, the CYMA Complete V2 Gearbox for SMG-5/MP5 AEGs w/High Torque Motor is a fine option! A complete V2 gearbox with MP5/SMG-5 specific parts and a high torque motor included, this set is designed as a drop-in replacement for most MP5/SMG-5 AEGs, the easy route to fixing up a faulty AEG.

Please note: This gearbox is only for the standard length SMG-5/MP5A and SD series. If you're after a gearbox for an SMG-5K/MP5K or PDW, you'll need an MP5K-style Version 3 gearbox.

If your Airsoft AEG is experiencing internal issues and you want a fresh start, this is a great choice! The CYMA Rear Wired V2 M4 Gearbox is an OEM replacement part; it is identical to the V2 gearbox that comes in standard CYMA models. It features a robust design, an alloy gearbox shell, an aluminium cylinder and a steel spring guide and spring.

It also comes pre-wired with a mini-tamiya connector and the motor connectors to attach the long shaft standard motor, which is also included. This gearbox is designed to be a drop-in replacement part; however, it is recommended that you have some technical knowledge for a smooth installation!

If you need a total fix for your Airsoft V2 gearbox AEG, the CYMA Rear Wired V2 M4 Gearbox is an excellent choice! It is also compatible with most V2 upgrades, making it ideal for upgrading in the future.