Shim Sets

Shim Sets may not be the most eye-catching parts of an AEG gearbox, but they have a huge impact on performance, noise levels and the service life of the internal components. Thin shims are used to precisely align the gears so that they mesh smoothly and efficiently.

Go straight to the relevant information:
• Why choose high-quality shim sets?
• What exactly does shimming do?
• Why is proper shimming so important?
• How can you tell if a gearbox has been poorly shimmed?
• More shims do not automatically mean better results
• Different shim thicknesses
• Top brands for shim sets
• Professional use
• What should you look out for when buying shim sets?
• Frequently asked questions about shim sets

In this category, you’ll find high-quality Shim Sets from brands such as Element, EPeS, G&G, Guarder and Specna Arms. The different shim thicknesses allow you to fine-tune the gears, whether you’re carrying out standard maintenance or rebuilding a complete gearbox.

Whether you’re fitting a new gearset, replacing bushings or overhauling a complete gearbox, shimming correctly is one of the most important steps in ensuring a smooth-running and durable AEG.

Why choose high-quality Shim Sets?

Although shims are simply thin metal spacers, they play a major role in determining how smoothly the gears turn within the gearbox. The correct combination of shim thicknesses ensures precise alignment, reduced friction and a longer service life for the entire drivetrain.

A well-shimmed gearbox runs noticeably more smoothly, produces less noise and puts less strain on both the engine and the gears during each firing cycle.

What exactly does shimming do?

Shimming is the process of precisely adjusting the position of the gears within the gearbox. Thin shims are used to ensure that each gear rotates at exactly the correct height and meshes correctly with the adjacent gear.

The aim of shimming is not to fit the gears as tightly as possible, but rather to find the right balance. There must be sufficient space to allow the gears to turn freely, whilst preventing excessive play.

A correctly shimmed gearbox offers a number of advantages:

• Less mechanical resistance.
• Smoother-running gears.
• Less noise when firing.
• Less wear on gears, bushings and bearings.
• More efficient operation of the entire gearbox.

Precisely because all the gears work together, the adjustment of a single gear affects the rest of the drivetrain. That is why, during a gearbox overhaul, the entire gearset is always examined, rather than a single gear.

Why is proper shimming so important?

A gearbox in which the gears have not been shimmed correctly may still function, but will almost always operate less efficiently. If the gears have too much play, the teeth do not mesh as precisely. If, on the other hand, they are fitted too tightly, this creates extra friction, forcing the motor to work harder.

Incorrect shim adjustment can lead, amongst other things, to increased noise, higher temperatures, higher power consumption and accelerated wear of the gears, bushings and the motor. In the long term, this can even cause damage to the internal components of the gearbox.

That is precisely why experienced airsoft technicians pay close attention to shimming each gearbox correctly. A good shim adjustment may not be immediately obvious, but it makes a huge difference to the reliability and lifespan of an AEG.

How can you tell if a gearbox has been poorly shimmed?

A gearbox does not necessarily have to be faulty to suffer from incorrect shim adjustment. Often, clear signs can be heard or felt before any actual damage occurs.

You can recognise a poorly shimmed gearbox, for example, by a rough or grinding gear noise, an engine that runs hotter than usual, or a replica that is less responsive when firing. Accelerated wear on gears, bushings or bearings can also indicate incorrect alignment.

If you notice one or more of these symptoms, it is advisable to have the gearbox checked before further wear and tear occurs.

More shims do not necessarily mean better

A common misconception is that a gearbox always performs better when more shims are fitted. In reality, it’s all about getting the right number.

Too many shims can cause the gears to be pressed too tightly together. This increases friction, forces the motor to work harder and generates extra heat. Conversely, too few shims result in excessive play, causing the gears to mesh less precisely and wear out more quickly.

The aim of shimming is therefore not to eliminate all play, but to give each gear just enough freedom of movement so that it can turn smoothly and efficiently.

Different shim thicknesses

Shim sets consist of thin metal shims in various thicknesses. By combining these, each gear can be adjusted individually and with great precision.

For example, many shim sets contain shims of 0.1 mm, 0.2 mm and 0.3 mm. By combining different thicknesses, the ideal alignment can be achieved without placing unnecessary stress on the gears.

It is precisely these small differences that ultimately make the difference between a noisy gearbox and one that runs smoothly, quietly and efficiently.

Top brands in Shim Sets

In this category, you’ll find high-quality Shim Sets from manufacturers renowned for their precise dimensions and reliable quality.

EPeS and Guarder are among the most popular choices amongst experienced airsoft technicians thanks to their consistent dimensions and high-quality finish. In addition, Element, G&G and Specna Arms also offer reliable shim sets for both maintenance and complete gearbox builds.

Practical tip

Are you replacing the gearset, bushings or bearings in your gearbox? If so, always re-check the shimming. Even slight differences in size between old and new parts can mean that the existing shim adjustment is no longer optimal.
After shimming, always check that the gears continue to turn freely before closing the gearbox completely.

Professional use

In a professional gearbox build, shimming is regarded as one of the most important steps in the tuning process. Experienced airsoft technicians take the time to align each gear individually, so that the entire drivetrain runs as smoothly as possible and the load is distributed evenly.

A correctly shimmed gearbox not only runs more quietly, but also places less strain on the engine, generates less heat and extends the service life of the gears, bushings and bearings. This is precisely why the shimming is almost always re-checked after replacing gears, bushings or bearings. Precise adjustment pays far greater dividends in the long term than simply fitting high-quality parts.

What should you look out for when buying a Shim Set?

Although shim sets may seem universal, it is important to choose a high-quality set with different thicknesses. Only then can you adjust the gears accurately and prevent unnecessary wear and tear.

In this regard, please bear in mind, amongst other things:

• A range of shim thicknesses for precise adjustment.
• High-quality finish and dimensional stability.
• Suitable for both maintenance and complete gearbox builds.
• Compatibility with the gears and bushings used.
• Enough shims to adjust each gear individually.

A high-quality shim set may be a small component of the gearbox, but it plays a major role in the reliability of the entire drivetrain.

Shim sets inside the gearbox

Shim Sets ensure that the gears inside an AEG gearbox are perfectly aligned. By using the correct number of shims, the gears run smoothly, the load is distributed evenly, and noise and wear are significantly reduced. Although shims may seem small and simple, they are an essential part of a reliable and durable gearbox.

Are you carrying out a complete gearbox overhaul, or are you also replacing other internal parts? If so, take a look at our AEG Gearbox Parts category, where you’ll find all the parts you need to fine-tune your gearbox to perfection.

Common mistakes

Shimming a gearbox may seem simple, but even small deviations can have a major impact on the performance and service life of the internal components.

Common mistakes include:

• Thinking that more shims are automatically better.
• Shim just one gear instead of the whole gear set.
• Closing the gearbox without checking that the gears move freely.
• After replacing gears or bushings, leave the existing shims as they are.
• Using shims of different qualities or thicknesses together without checking the fit.
• Mistaking the noise for a poorly tuned engine, when the cause is actually down to the shimming.

By working calmly and carefully, you can prevent a great deal of unnecessary wear and tear and ensure that the gearbox continues to run smoothly for years to come.

Frequently Asked Questions about Shim Sets

Do I need to re-shim when I’m only replacing the gears?
Yes. Even if the new gears have the same gear ratio, minor manufacturing tolerances may mean that the existing shim adjustment is no longer optimal.

Do I need to re-shim when I replace bushings or bearings?
Yes. New bushings or bearings may differ slightly in size from the old parts. This changes the position of the gears, so re-shimming is strongly recommended.

Are shim sets universal?
Most shim sets are universally compatible with AEG gearboxes. However, it is important that the set contains shims of different thicknesses, so that you can adjust each gear precisely.

Can poor shimming cause damage?
Definitely. An incorrectly shimmed gearbox can lead to increased noise, higher temperatures, extra wear on the gears, bushings and motor, and in some cases even to broken gears.

Does a well-shimmed gearbox really make a difference?
Absolutely. A correctly shimmed gearbox runs more smoothly, more quietly and more efficiently. What’s more, the load is distributed more evenly, which can significantly extend the service life of the internal components.

Advice from Airsoft-Legends

Shimming is perhaps one of the least visible tasks when working on an AEG gearbox, but at the same time one of the most important. A high-quality gearset or powerful motor only really comes into its own when the gears are correctly aligned.

We therefore recommend that you always re-check the shimming after replacing gears, bushings or bearings. Take your time with this and do not try to eliminate all play; instead, aim for the right balance where the gears can turn freely without excessive movement.

With high-quality Shim Sets from Element, EPeS, G&G, Guarder and Specna Arms, you lay the foundations for a quiet, efficient and durable gearbox that will continue to perform reliably for years to come.