Description
Lonex L4-A1 Full Gearbox Set (SP120 Original Type)
This is a complete, ready-assembled gearbox from Lonex in its SP120 Original Type configuration. Lonex is a long-established maker of AEG internal parts, and its complete gearbox sets are designed as drop-in replacements for the stock gearbox in M4-pattern AEGs, giving you a whole upgraded unit rather than a box of parts to assemble.
The SP120 Original Type sits in the middle of the Lonex range, pairing an SP120 spring with an original (standard) gear ratio. It is a sensible choice for players who want a reliable, upgraded gearbox for an everyday M4 without making the gun faster or slower than standard. It is also an easy fix for a rifle whose original gearbox has failed.
Build and internals
Retailer listings for Lonex’s M4-A1 SP120 complete gearbox describe a Version 2 shell with 8mm ball bearings, an enhanced steel gear set, a polycarbonate piston with steel teeth and an aluminium piston head, a steel cylinder with aluminium cylinder head, an air seal nozzle, a steel ball bearing spring guide and low-resistance wiring. These upgraded parts are designed to handle regular use better than many factory gearboxes, and because the set comes assembled, it saves the time and tools needed to build a gearbox from scratch.
Choosing a type
Lonex offers this set in several configurations. The SP120 Original Type uses a standard gear ratio for a balance of trigger response and pull on the spring. The SP100 High Speed Type is geared for a faster rate of fire, while the SP150 Ultra Torque Type is aimed at pulling stronger springs. Choose the type that suits how you play, and remember that power output always needs to be checked against your site’s limits.
Fitting
Swapping a complete gearbox is a lot simpler than rebuilding one, but it still means stripping the lower receiver. Remove the battery and magazine first, note how the existing wiring is routed, and check whether your replica is front- or rear-wired before ordering. Once fitted, set your motor height and test fire with a chronograph before taking it to a game.
Key features
- Complete, assembled Lonex gearbox set
- SP120 spring with original (standard) gear ratio
- Version 2 gearbox shell with 8mm bearings (per retailer listings)
- Enhanced steel gears
- Polycarbonate piston with steel teeth and aluminium head
- Steel cylinder and steel ball bearing spring guide
- Low-resistance wiring
- Drop-in replacement for many M4-pattern AEGs
Compatibility
Designed for M4-pattern AEGs that use a Version 2 gearbox. Small differences between manufacturers’ receivers mean some bodies may need minor fitting work, and some guns may not accept it at all. Check whether your replica is front- or rear-wired, and confirm the configuration with us before ordering if you are unsure.
Care and maintenance
Use good-quality seamless BBs and a battery and motor suited to the gearbox. Avoid storing the gun with the spring compressed: fire a shot on semi-auto before putting it away. Keep the hop-up and inner barrel clean, and have the gearbox inspected and re-greased if you notice changes in sound, rate of fire or trigger response.
Who is it for?
For M4 AEG owners who need a replacement gearbox, and for players who want a ready-built, upgraded unit with a standard ratio rather than building their own.
Please note: Motor, battery and outer parts are not listed as included. Check your power output with a chronograph after fitting and stay within your site’s limits.
