How to Convert an Airsoft Gun from an AEG to an HPA

Last Updated: September 16, 2021

Many people want to convert their airsoft AEG to an HPA, as it is easy to adjust the FPS, it is quiet, it has an instant trigger response, and makes your shot more consistent. Although, after converting you will need an HPA rig, which includes the air tank, a regulator, and something to carry the air tank in. Before beginning, make sure your primary field allows HPA setups, as some fields don't.

Steps

1
Remove the gearbox from the gun. Every gun is different, but you should be able to get to the internals by popping out pins and screws that keep the body halves together. Make sure you keep the screws.
- Once the body is separated, you should see a large metal piece that would have some wires running into it. This piece is the gearbox.
- There may be some screws holding the gearbox down, if so you can remove them.
- Remove the gearbox from the gun by lifting the gearbox and the motor (a cube like structure likely located in the pistol grip). Set them aside and move the body out of the way.
2
Open the gearbox. You can open the gearbox by removing screws keeping the halves of the gearbox intact. Make sure that the front of the gearbox is on your right. You can now lift up the top shell of the gearbox, which should reveal many gears and pistons.

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3
Gut the Gearbox. You will need a screw-driver for some of this. You will want to remove things in this order:
- Spring and buffer-tube/spring-guide. Make sure you keep the buffer-tube/spring-guide.
- The bevel gear. This is the gear the will be closest to you.
- The piston system.
- The other two gears.
- The the trigger and trigger spring. You will need to keep these and the trigger screws for later on.
- The trigger contacts and wiring.
- Anything else left in the gearbox.
4
Install the trigger board. Using the trigger screws you removed, place the trigger board where the trigger contacts once were, and screw it in.
5
Install the main HPA module. Take the main module and place it where the piston once was, making sure the notches on the gear box and main module are aligned.
6
Connect the trigger board and the main module. Take the wiring from the main module and plug it in to the trigger board.
7
Connect the wiring harness. Take the wiring harness and snap it into the trigger board.
8
Position the HPA tube. The tub should be run down the pistol grip area of the gearbox.
9
Position the wiring harness. The wiring harness will follow the path of the cables going to the battery that were removed.
10
Reinstall the trigger. Put it back in just as you removed it. Place the trigger over the trigger spring. Make sure that the trigger and trigger spring are aligned correctly.
11
Reinstall the buffer tube. Make sure it is facing toward the main HPA unit.
12
Close the gearbox. Put the other half of the gearbox back on, make sure nothing is getting pinched, and screw the halves back together.
13
Put the gearbox back into the gun. You can now close the gun, and you are finished.

Community Q&A

Question

What is a wiring harness?

Kurtis Hardy

Community Answer

Wiring harnesses are what come with an HPA unit to hook from the trigger board to the Fire Control Unit (FCU). Most electronic HPA units will come with everything needed to assemble it into your favorite Airsoft replica.
Question

Where can I find an HPA engine?

Kurtis Hardy

Community Answer

Airsoft HPA engines are available from many Airsoft vendors. One vendor that is highly recommended is Amped Airsoft. They offer a wide variety and can also be purchased in kits with everything you need to install.