Shimming is one of the most critical steps in building or upgrading an airsoft gearbox. A properly shimmed gearbox reduces wear, improves efficiency, increases rate of fire, and prolongs the life of your internal components. At JVAN Airsoft, we specialize in high-performance gearbox systems, and in this guide, we’ll walk you through a professional approach to shimming.

Why Proper Shimming Matters

Shimming involves placing thin metal spacers (shims) around the gears inside the gearbox to align them perfectly. Poor shimming can lead to:

• Excessive noise and vibration

• Increased motor and battery strain

• Premature wear on gears and bushings

• Inefficient power transfer

Using high-quality shims—such as 0.1mm and 0.5mm variants—is essential for fine adjustments. At JVAN Airsoft, we recommend using precision shims to achieve optimal results.

Step-by-Step Shimming Guide

1. Gearbox Preparation

Before shimming, ensure the gearbox shell is clean and free of grease, cables, and other components. Remove the trigger, safety lever, and tappet plate to access all bushings freely. Check that all bushings or bearings are correctly installed and undamaged. They should be flush with the gearbox shell and firmly seated.

2. Shim the Spur Gear First

Begin with the spur gear. Place two 0.1mm shims under the gear and test the fit by closing the gearbox halves (without screws). The gear should spin freely but with minimal vertical play. Use a screwdriver to gauge movement if needed. Adjust shim thickness until the gear rotates smoothly without binding. Secure the gearbox with screws to confirm the tolerance remains correct under tension.

3. Shim the Sector Gear

Install the sector gear with an initial shim setup (e.g., 0.2mm at the bottom). Check vertical movement and add or remove shims until the gear spins freely. Avoid using a single thick shim; instead, use multiple thinner shims for finer adjustment. This ensures compatibility with the piston and tappet plate later.

4. Check Spur and Sector Gear Interaction

Once both gears are individually shimmed, test them together. Rotate the gears and listen for grinding or rubbing. If the sector gear rubs against the spur gear, adjust the shimming—usually by raising the sector gear slightly with an additional 0.1mm shim. Ensure the gears mesh smoothly without friction.

5. Shim the Bevel Gear

The bevel gear must align perfectly with the motor’s pinion gear. Start by centering the bevel gear in the gearbox using equal shims on both sides. Check vertical play and adjust until the gear moves slightly but doesn’t bind. To verify height, look through the motor opening and ensure the bevel gear teeth are centered relative to the gearbox edge. This step may require trial and error.

6. Final Assembly Check

Install all gears together and test the rotation. The gear train should spin freely with minimal resistance. Listen for unusual noises or binding. If any gear feels stiff, re-check the shimming for that specific gear. Remember: using bearings (instead of bushings) may require slightly more play to avoid pre-loading the gears.

Pro Tips from JVAN Airsoft

• Always use a mix of shim sizes (0.1mm, 0.2mm, 0.5mm) for precision.

• Avoid lubricating gears during shimming—grease can mask fit issues.

• Keep gears organized and track shim placement to avoid confusion.

• When using aftermarket gears, note that some may require filing or grinding to avoid interfering with the piston or tappet plate.

• For best results, use original manufacturer parts (gearbox, grip, motor) to ensure compatibility.

Upgrade with JVAN Airsoft Components

Shimming is a skill that combines patience and precision. If you’re looking to upgrade your internal components further, explore JVAN Airsoft’s range of high-quality gears,bushings, Cylinder Head, and more.

For more tutorials, product highlights, and technical guides, visit our website at https://www.jvanairsoft.com and follow us on social media for the latest updates and expert tips!

Business Development

• Heidi
• JIN WANG METAL(HK) LIMITED
• Whatsapp：+8618103050072
• E-Mail :heidi@hardwareprecision.com