What Do Airsoft Gear Shims Fix

Shims are ultra-thin metal washers placed on gear axles to control horizontal side-to-side play and set correct tooth contact between gears. Without proper shimming, gears can rub against the shell or each other, run loud, and wear down unevenly, even if every part in the gearbox is otherwise high quality.

How to Shim an Airsoft Gearbox

Start clean: degrease and dry the gears and gearbox shell completely, since leftover oil or debris will throw off your measurements. Install the bevel gear and motor first to set motor height and confirm quiet, proper contact between the motor pinion and bevel gear teeth. From there, place shims on the bottom and top of the spur and sector gears one at a time, closing the shell with screws each time to test fit before making further adjustments.

Airsoft Shim Tolerance

The target is a barely perceptible side-to-side movement, roughly 0.1mm, with each gear spinning freely and not rubbing against the shell or adjacent gears. Too tight and gears bind or wear prematurely. Too loose and you get noise, inefficiency, and accelerated tooth wear from imprecise contact.

Airsoft Shim Materials and Increments

Precision CNC laser-cut stainless steel shims, commonly available in 0.1mm and 0.05mm increments, avoid the burrs and uneven stacking that lower-quality shims can introduce. Stacking multiple thin shims to reach your target gap is normal and often more precise than trying to find one exact-thickness shim.

What to Look for in Airsoft Shims

A few details determine whether your shimming holds up over repeated use.

Precision and Consistency

CNC laser-cut shims hold consistent thickness across the set, which matters when you're stacking multiple shims to hit an exact gap.

Increment Range

Having both 0.1mm and 0.05mm increments on hand gives you finer control than working with only one size.

Material Quality

Stainless steel resists burrs and deformation better than cheaper stamped alternatives, which matters for a precise, lasting fit.

Airsoft Gear Shim FAQ

Why is my airsoft gearbox loud?

Improper shimming is one of the most common causes, letting gears run with too much play or uneven tooth contact rather than a precise, quiet mesh.

What's the correct shim tolerance?

Aim for a barely perceptible side-to-side movement, around 0.1mm, with each gear spinning freely without rubbing.

Do I need to shim a brand new gearbox?

Many stock gearboxes benefit from re-shimming even out of the box, since factory shimming isn't always precise. It's a common first upgrade step for a new build.

Can bad shimming damage my gears over time?

Yes. Uneven tooth contact from poor shimming accelerates wear on the gear teeth themselves, shortening their lifespan even if the gears are otherwise high quality.

Should I clean the gearbox before shimming?

Yes. Degrease and dry all components first, since leftover oil or debris can skew your gap measurements during the process.