Document the baseline
Photograph wire routing, selector parts, trigger components, tappet and nozzle position, anti-reversal latch, motor orientation, and the original shim arrangement before removing parts.
WORKSHOP GUIDE
Airsoft Gear Installation & Shimming
Plan a controlled AEG gear installation, establish smooth gear alignment, and check motor-to-bevel mesh before completing a low-risk initial test.
BEFORE OPENING THE GEARBOX
Work safely and preserve the original setup
Disconnect the battery, unload the replica, wear eye protection, and control the spring during disassembly. If you cannot identify the spring-release risk or reassemble the gearbox confidently, use an experienced airsoft technician.
Stop when damage is visible
Do not reuse cracked gears, distorted bushings, damaged piston teeth, a deformed shell, chipped pinion teeth, or parts that bind before the shell is fully closed.
WORKBENCH
Useful tools and materials
Clean measuring and test tools make the process repeatable. Exact tool needs vary by gearbox.
MEASURE
Shims and inspection tools
Quality shims in suitable diameters, calipers where needed, good lighting, a magnifier, and a non-marring pick or tweezers.
ASSEMBLE
Correct hand tools
Drivers matched to the fasteners, shell-holding aids, cleaning cloths, suitable degreaser, and controlled spring-compression tools where required.
FINISH
Compatible lubricant
Use a light, suitable gear lubricant. Excess grease increases drag and can migrate into areas where it does not belong.
CONTROLLED SEQUENCE
A practical installation and shimming order
There is no universal shim stack for every shell. The objective is smooth rotation, correct gear mesh, and minimal axial movement without binding when the shell is fully tightened.
Clean and inspect
Remove debris and old contaminated grease. Inspect the shell, bearing or bushing seats, gears, shafts, piston rack, anti-reversal latch, and related parts.
Seat bushings or bearings
Confirm they are fully seated, secure, aligned, and appropriate for the shell. A raised or loose bushing changes the entire shim calculation.
Set the bevel gear
Establish stable bevel positioning and motor-to-pinion mesh. Check motor height and contact pattern without forcing the gears together.
Add the spur gear
Shim the spur for correct engagement with the bevel while maintaining clearance from the shell, bushings, and nearby components.
Add the sector gear
Verify spur-to-sector mesh, piston pickup, tappet interaction, cutoff or sensor relationship, and clearance through the full cycle.
Close and tighten the shell
Test with the shell fully closed and fasteners evenly tightened. A gear train that spins freely in an open shell can bind after closure.
BEFORE POWER
Final mechanical and electrical checks
Complete the checks below before a controlled first cycle.
Rotate by hand
With the main spring removed or otherwise safely unloaded, rotate the gear train by hand and confirm smooth movement with the gearbox shell fully closed and tightened. Do not force a loaded gearbox through a full cycle.
Test conservatively
Confirm wiring and polarity, use a known-good battery of the correct chemistry and voltage for the replica and ETU, and begin with short controlled cycles. Stop immediately for grinding, screeching, lockup, smoke, or rapid heat.
COMMON QUESTIONS
Gear installation and shimming FAQ
Answers to common questions before closing and testing an AEG gearbox.
How much side-to-side movement should an airsoft gear have?
The goal is minimal axial movement without creating binding when the gearbox shell is fully closed and tightened. A universal numeric clearance is not reliable across different shells, gears, bearings, and bushings.
Which gear should I shim first?
A common method begins by establishing bevel-gear and motor-pinion alignment, then adding the spur and sector gears. The exact workflow may change with the gearbox design and the technician's measurement method.
Should gears spin freely with the gearbox shell open?
Open-shell movement is only an intermediate check. The important result is smooth rotation with the shell fully closed, evenly tightened, and all intended mechanical relationships verified.
How much grease should I apply?
Use a light, even amount of a compatible lubricant on the working surfaces. More grease is not automatically better; excess can increase drag and spread into the trigger, electronics, or compression system.
