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There are many internal parts inside airsoft guns that make them function. Many of these parts are able to be replaced or upgraded to enhance AEG performance. If you haven't performed gearbox work, we recommend using our custom upgrade and repair service. You can have an experienced Fox Airsoft Gun tech perform the work for you. Below we've listed some of the internal components inside your gearbox.
The spring inside an AEGs gearbox is what provides the force to push the piston. The piston creates air compression in the cylinder and pushes the air into the barrel through the nozzle. This is the component that you would change first to upgrade or downgrade the velocity of your gun. Any other components changed that affect velocity would be only for fine tuning or efficiency sake.
For velocity measurements in airsoft, you will see feet per second (fps), meters per second, and occasionally joules. In the United States we'll often quote a guns performance by its FPS. However the springs tend to be rated in meters overseas and performance still being stated in joules and feet per second, even though it should be all metric overseas. Confused yet?
The springs are pretty straight forward once you look at it. The springs will be stiffer for the higher fps applications. Some brands will use color coding to help identify what spring you have in a gearbox which is really handy for techs. The length of the spring does not play a factor in the stiffness though the longer ones can be a nuisance to install. Do they hold their tension longer? We do not have any evidence that would suggest yes or no yet. Your spring tension is the key to holding the same level of performance over time if your compression parts are in top shape. Leaving your gun with its piston cocked for periods of time will cause your spring to lose tension and thus FPS. To avoid this, you'll want to decompress the spring before you put the gun away. Usually giving the gun a few cycles to hopefully return the gearbox back to its starting position will be the best way. It's not an exact science but it will do. Some guns such as the ICS UK1 series can mechanically decompress the spring, keeping your tension longer.
Standard spring guides will typically be plastic or cast metal from the factory. Spring guides are not known to break but it is not in the realm of impossibility. Spring guides can be upgraded to improved designs such as ones that have bearings. The bearings increase the life of your spring by preventing the spring from binding. The bearings do this by providing some give for the spring as the coils may want to naturally turn and rotate when under tension. One byproduct of running an aftermarket spring guide is that sometimes these bearings increase the tension of the spring and can increase velocity a tiny bit. The space occupied by the bearings will pre-compress the spring.
A spring guide is pretty simple so you can pick whatever one works. There is a potential for failure for multi-piece units that are built poorly but this is exceptionally rare. The same goes for the bearings but these don't spin at a tremendous speed, so again having a failure here is pretty rare and exceptional. Remember the more complexity you add to a basic part the more likely you can induce new problems when things wear out. We've been working on our guns for many years and just when you think you've seen it all there's always something new.
The selector plate is an internal component found on the outside of the gearbox. It is usually a long plastic piece (sometimes metal) and is captured so it does not come off the gearbox. Manipulating it changes the fire modes that the gearbox will perform. The function of the selector plate is to interface with the external fire selector on your AEG and tell the gearbox what mode it should be firing in. It does so by mechanically positioning the cutoff lever to the spot that will allow it to fire full auto or semi auto or stop the trigger in safe. Some gearboxes also use the selector plate as an additional contact for a current to go through so you have a hard cutoff for the electricals when you position your fire selector in safe. The contact is a metal piece on the selector plate and can be omitted if your system does not require it. You will typically see it utilized in M4 and AK style gearboxes but maybe in some others as well. You can determine if that contact is needed by looking at the switch assembly and seeing if the wires are routed to additional contacts that would touch the selector plate or if the wires would run a continuous circuit to the motor. Be careful you do not acquire the wrong type of selector plate (such as an all metal one) for a system that uses the selector plate to conduct. You will have a short on your hands. Selector plates are specialized to the model of gun they were designed for unlike the gearbox which may be used in more than one style of gun. The version number will be irrelevant to the application.
The piston head is a component found in AEG (automatic electric gun) gearboxes. The piston head is mounted to the piston body and has an o-ring installed on it which creates compression. As the piston is drawn back during the firing cycle, the piston is set far back in the cylinder. Once the gears have made the proper revolutions the gear releases the piston which will slam forward into the cylinder head. Air is compressed in the cylinder with the piston head o-ring and is forced through the cylinder head and then nozzle and then hopup unit.
Typically this component will be made of high strength polycarbonate though some manufacturers might use aluminum to make it more durable. What is better? Our school of thought is that if you are replacing or upgrading parts, making one part stronger than the rest means the next weakest part will be the one to fail or live a shorter than average lifespan. The polycarbonate piston heads will last tens of thousands of rounds before they wear out and fail on a good AEG. An aluminum one though would last indefinitely. Why wouldn't you want to upgrade to a metal one though? Consider what we just said about the next part failing. Now with the metal piston head you have something not only tougher but more importantly you have a heavier piston slamming the cylinder head and putting more stress on the gearbox when fired.
Virtually all piston heads in every gun we see these days and as separate upgrade parts will be ported. The porting which appears as holes on the front of the piston head directs some of the air being pushed during the compression phase of the shot cycle to flair out the piston head o-ring to give better compression. Even stock polycarbonate piston heads will last indefinitely so we recommend not worrying about this component until it fails. You'll know when it fails when you are firing your gun and though it sounds like it is cycling you are having velocity issues and the BBs just barely come out of the gearbox.
The piston body is a high stress component found inside the gearbox. The piston assembly will include a piston body and a piston head with piston head o-ring. The base of the piston head is secured inside the piston body and may or may not contain bearings. The piston body is a 14 or 15 tooth style which is found in just about every AEG. There are others which can easily be identified by the number of teeth they have.
The job of the piston push air into the hopup chamber by compressing air in the cylinder and forcing it forward using the seal created by the piston head. The piston is cocked by using the gears and the spring is the component responsible for driving the piston forward. The stiffness of the spring dictates the force of the piston going forward which in turn dictates how hard the air will be pushed out. Springs with greater stiffness will give you better velocity however does increase wear and tear on the piston and other supporting components.
The piston is considered high stress as it sees a lot of wear and tear from its two functions. Being positioned by the gears, you have gear to piston teeth contact. If you have any misalignment between the piston and the gears you could potentially stripped the teeth off of either components. This would occur if you have a compression jam - a jam in which the BB does not leave the barrel and the air that is being forced by the piston has no where to go and the piston is air blocked and cannot move as it should. The gears will then catch on the piston at the wrong moment causing damage.
Then you have the actual force of the piston hitting the front of the gearbox when it completes a cycle. The amount of force it hits with is pretty significant and might be worsened if you upgrade to a stronger spring. Typical damage you will see here would be more so in the piston head. This is the component that makes contact with the cylinder head/front of the gearbox. Should this component break, the piston body will be off alignment and continual attempts to fire will cause the gears or piston to strip in addition to the already damaged piston head. Your gun will exhibit very low FPS if your piston head or its seal is compromised. Upgrading to a metal piston head will make this component more durable but it will add additional stress to the front of your gearbox due to the heavier weight now slamming forward from the heavier piston head.
Sometimes when upgrading your gearbox components, it is best to consider what you want the weak point in your gearbox to be. If you upgrade one component, the next one is now going to be the one that gives if there is a failure due to not being built as strong. Often times it is best to make sure that even though upgraded, you be mindful of what components would be the least expensive to replace. Having a $20 piston go bad is preferred over a $100 gear set.
The motor is a component that drives the gears inside the gearbox. It is usually located in the pistol grip of most AEGs and in the body for true support weapon style AEGs. The motor is connected to the electrical system through the switch. When the switch circuit is closed, energy is flowing from the battery through the switch and comes to power the motor. The motor will spin the shaft which has a pinion gear attached. The pinion gear turns the bevel gear, which turns the spur gear, which turns the sector gear, which pulls back the piston and releases it.
The motors in an electric gun are what are known as brushed motors. They use magnets and a spinning armature inside the body. Since the armature rotates, it is called a rotor. The rotor is turned into an electromagnet when electricity flows through it. As the rotor spins, it is interacting with the magnets for a push/pull effect. The brushes rub on the end of the motor to provide the electricity. The brushes are a wear item since they make friction and can be worn out over time. The brushes can be replaced pretty easily however.
One way you can augment the performance of your AEG is by upgrading the motor. Upgrading to a motor that has more torque than your original motor can be beneficial in a few ways. This is a very easy upgrade for guns where the motor is housed inside the grip and is one of the easiest things you can do. If you leave the rest of the gun stock, you will likely see an improvement in the rate of fire. A better motor will also turn the same gearbox setup (gear ratio and spring) with less effort due to putting out more torque, so you may see an increase in efficiency as a byproduct. One thing to note when selecting a motor is to make sure the shaft length is the same as your original motor. The majority will use long shaft type motors.
Besides the motor and hop up, any other modifications and upgrades will all be done inside the gearbox which requires considerable skill and time and are not suited for novices.
The function of the gear set is to take the energy being output by the turning of the motor into a means to pull back the piston inside the gearbox and releasing it, ultimately firing the electric airsoft gun. A traditional gearbox will have three gears: bevel, spur, and sector. The pinion gear which is mounted to the motor shaft will turn and rotate the bevel gear, and then the rest will turn with it. These all interact with each other and ultimately that energy is being used to turn the sector gear which in turn pulls back the piston.
Most AEGs will come with a standard gear ratio of about 18:1 and you should stick to that unless you have a specific performance goal in mind, in which you should build around a specific gear set and velocity you are looking for. Lower numbers indicate a faster gear ratio (such as 16:1, 14:1). Your gears turning faster will translate to a faster rate of fire if everything else is left stock. If you mismatch a heavier spring to a faster gear ratio your battery draw will be pretty high but you could still see an improved rate of fire. Motors and upgraded batteries are an easier route to explore than the gear set because of the time and effort it takes to install a gear set properly.
Gear sets are made to be pretty strong however if you do start modifying your airsoft gun just be aware that the weakest part will give and usually these parts are balanced from the factory so that damage will typically harm inexpensive components first. It will still be a major inconvenience because you have to have the gun repaired but if you compare a piston to gear set, a piston costs half or even a third of what a gear set costs. Sometimes upgrading to a very strong piston means damage that would have otherwise damaged the piston is now damaging the gears. Air seal related jams (BB jams) will force air into the gearbox since the BB cannot escape. That air pressure can cause the piston to be pushed back and the gears will be making contact with the piston at an incorrect alignment due to the timing being thrown off.
The cylinder head is a component inside of the gearbox of an AEG. The cylinder is mated to this component and the piston creates air compression inside the cylinder and forces are through the cylinder head and then through the nozzle. The spring controls how hard the piston is being driven forward.
The stock cylinder head in most guns is made of polycarbonate plastic with a rubber pad inside that absorbs the impact. Occasionally some manufacturers opt to use metal cylinder heads instead. Durability on the cylinder head is indefinite even on the plastic ones however the rubber o-rings which help seal with the cylinder itself can be damaged or dry out with age. Very rarely does a plastic cylinder head physically break but it is not impossible. In fact rarely should you replace this component unless it is damaged already or you are already doing other upgrades.
Having good air seal is the key to maximum efficiency and consistent velocity from inside your gearbox. Places you can tune for air seal are: the seal between the cylinder head and cylinder, the nozzle to cylinder head, the piston head o-ring to the cylinder assembly. You can test by putting your finger over the air seal nozzle port and pushing the piston into the cylinder assembly. You should feel some resistance from the piston because of the air pressure being trapped from your finger. The harder you push, the piston should be able to compress. It is okay if a little air escapes from your finger through the nozzle. What you are trying to feel and listen for is if the air is being lost elsewhere (like between the cylinder head and cylinder). If you have a leak there that can be remedied by new o-rings, a different cylinder head that fits better, or even plumbers tape. If you can push the piston and it won't move at all and all the air is trapped, that is the best possible air seal you could ask for.
Since every component has a failure point and give, it is important to understand that making one component more durable might actually shorten the life of another component. For example, upgrading to a metal piston head will surely destroy a stock plastic cylinder head. Metal components are not always necessary and can cause more damage than help, such as the case with piston heads. A stock polycarbonate piston head can have a service life of 15,000 to 25,000 rounds before needing replacement in many cases.
The cutoff lever is a component inside the gearbox of an electric gun and it makes possible the semi-auto function. Without a functioning cutoff lever your gun will only go full auto. The cutoff lever interacts with the cam on your sector gear to give you semi-auto capability. When your selector is set to semi-auto, the cutoff lever can move to the open and close position with each rotation of the gear when the cam is touching it. When the cutoff lever gets tripped, it releases the shuttle on the switch assembly and interrupts the electrical current running through the contacts which gives you a single shot. For full auto, the cutoff lever is left in the open position where the cam will not touch it and the lever does not disrupt the trigger shuttle form making contact. It is hard to say what the service life for a cutoff lever will be as it depends on the materials it is made of as well as how tough the gear is that it interacts with. You will have metal to metal contact and typically the gear and cam on the gear will be much stronger than the cutoff lever.
The bushings/bearings are a component found inside the gearbox. They are responsible for holding the gears in position and bearing any load from the gears caused by rotation and the spring inside the gearbox. By default, some manufacturers use bushings which are simple in design and some will have bearings which feature small metal ball bearings and a multiple piece race/roller setup taking over the shape of a bushing. Every gearbox has a pair of bushings or bearings per gear, so typically a three gear configuration (sector, spur, and bevel gear) means you have six of these.
The anti-reversal latch is a component found inside an electric gun's gearbox. It makes it so that the gears can only turn in one direction and also to hold the position of the gear when they stop. Without it, when you fire your airsoft gun and let go of the trigger, the piston would just move back into the forward position on your own and you'll either have a BB come out of your barrel due to an incomplete firing cycle. Though this is not a breakage that is catastrophic to the functioning of the gun compared to many of your other internal components, the double feeding or incorrect cycling will still be an issue and the gun won't always be doing what it is supposed to. The anti-reversal latch will be made of metal but this part does get put through some stress and makes plenty of metal on metal contact, so it should be expected that this part may one day wear out and fail. Upgrading to an aftermarket anti-reversal latch can certainly add peace of mind however it is hard to ascertain how much more life you will be getting out of this component.
How do you know if your anti-reversal latch is not doing its job? Right after you release the trigger and your gun stops firing, you will hear a whirring sound after the release of every trigger pull. This is the sound of the gears not being stopped by the anti-reversal latch and spinning freely. The spring will push the piston forward since it is not being locked in place by the anti-reversal latch and the gears being allowed to spin the wrong direction.
When purchasing an anti-reversal latch, be sure to check the product description to make sure it is for your style gearboxes. There are a few different designs and these latches are not interchangeable. The gearbox version number is not a revision or a list that goes from worst to great. The gearbox version is just a general model design number that was devised by the original makers but formally adopted terminology industry wide.
Q: Can I just install a big spring to get a high velocity?
A: This is not recommended, whenever you increase the stress on the gearbox with a spring, you increase the stress on the different components. We always recommend upgrading your efficiency first, and the spring last. Often times you can get alot more out of a gun without ever touching the spring.
Q: Is an inner barrel important?
A: Absolutely! This is one of the best upgrades you can do for the money. A good tight bore barrel increases accuracy, range, and a slight increase in velocity. All of this can be accomplished without putting any additional wear and tear on your gearbox.