Welcome back readers, this is the installation guide to the GHK Gas Blowback Conversion Kit. It is designed to fit into most AEG bodies, and some modification may be necessary in order to get it into your rifle of choice. If you check out the Evike Product Page, they have a set of instructions for the kit and any modifications that are needed for certain manufacturer's M4 rifles. I suggest you print out a copy to look at while you put it together, just in case.
Tools I Needed:
- Nylon/Brass Hammer
- Assorted sizes of Pin Punches
- Long Shafted Philips Head Screwdriver (No.2 or No.3 head size)
- Standard Size Philips Head Screwdriver (No.1 preferred)
- Assorted Hex Head Screwdriver Sizes
- Q-tips
- Assorted Dental Picks (toothpicks make an okay substitute)
- Small round file (really small, around 1/8" diameter)
Step 1: Clear Your Rifle of All BBs and Remove All Magazines
This is going to get different for everyone else, but the premise stays the same. Make sure to clear your rifle in case you have a round you don't know about in the chamber. Simply take the rifle, remove its magazine, then in a SAFE DIRECTION, pull the trigger twice in semi auto. Usually I have a box with a few towels and a screen over it so the BBs don't bounce back and hit me. Always wear safety glasses when doing this as well, you never know who could have used your rifle last without you knowing. Once it is clear, remove all magazines and ammunition from plain view (and the room if you want to be extra safe).
Step 2: Separate the Upper Receiver from the Lower Receiver
Pretty simple. Each rifle is different though, so know how to take apart your rifle. If you don't ask your local tech to help you out.
For my G&P, I had to remove the front take down pin and slide forward the upper off of the lower. The rear pin doesn't hold the upper. The front is also self retaining, as in it can't be punched out of the lower because of a detent pin. The rear pin was not like this, so it is free to be removed from the body.
Step 3: Remove the Hop Up Unit from the Upper
This pretty simple as well. Most AEG hop up units slide out the back of the upper without any resistance. Make sure that any lose parts that fall out are accounted for. On my rifle, there is a faux bolt plate that just fell out. Some are mounted to the charging handle, but we will get there next.
Step 4: Remove the Charging Handle from the Upper
Again, pretty simple. For most rifles, the charging handle is held in with its own tension spring. Simply unhook and pull out from the back of the receiver. You will not need the spring, as the GBB kit comes with its own. Remove the faux bolt plate from your charging handle as well. it is usually held on with a screw or two, or could not be attached at all like mine.
For my G&P, there was a hex screw holding my spring inside of the upper. Once you are done, your charging handle will look like mine, nothing else attached to it.
Step 5: Disassemble the Hop Up Unit and Rebuild It Using the Parts in the GBB Kit
This is also a simple thing to do, as most techs can accomplish this in a few minutes. The GBB kit comes with a new hop up body, adjustment wheel, hop up nub arm, retaining o-ring, retaining clip, and steel pin. Remove the plastic C-clip from your AEG hop up unit and set aside. Pull the inner barrel and bucking slowly out the front. If the bucking gets stuck inside of the hop up body, use a blunt tool like a Q-tip to push it the rest of the way out. Next part might be a tough one, you need to get the nub out of the unit. The nub is a little rubber cylinder, tucked underneath the hop up arm. I used a dental pick to carefully remove it, but a tooth pick will suffice. Pictured below is the removed parts to the left (AEG hop up unit and plastic C clip), all the of the parts you will need to keep in the middle (inner barrel, hop up rubber, and hop up nub), and all of the GBB kit parts to the right.
To reassemble the GBB kit hop up, place the bucking onto the inner barrel in its correct orientation and slide it bucking from into the front of the GBB kit unit (opposite side of the wheel). When it is fully seated, the slots on the inner barrel will line up like it would on a normal hop up unit. Install the GBB kit plastic C-clip to retain the inner barrel. Next, place the nub into the top of the hop up unit (towards the front), and place the arm on top of it. There are two little fingers that will hold the cylinder in place on the hop up arm. Again, this should look similar to a normal AEG hop up unit. Once that is complete, press in the steel pin into the hole of the hop up body and hop up arm, going through the hole at the other side of the body. I found the pin was a little too small for the plastic, so I took a small round file and widened the hole just a little bit. Once I did that, the pin fit into the assembly snugly. Next, making sure the little tab at the back of the hop up arm is aligned with the curved slot in the hop up wheel. Push the wheel forward so the arm locks into that slot, and another slot will appear behind the wheel. Take the O-ring and mount it into this slot so it retains the wheel onto the rest of the assembly. The assembly is shown below, which is from GHK's instructions on Evike.com's product page for the GBB kit.
Now check to make sure the wheel can turn freely, check that the arm moves up and down, and look into the inner barrel to see if the nub is pressing down on the bucking properly. If it all works, then your hop up unit is fully assembled.
Step 6: Install the Hop Up and Inner Barrel, Mount the Charging Handle onto the Upper Half of the GBB kit, and Slide the Assembly into the Upper Receiver
This is a pretty easy step. Simply slide the inner barrel and hop up unit back into the upper receiver like it was the AEG one. It should fit into the barrel just like it was meant to be. Some filing may need to be done though. It should look like an ICS hop up unit once it is installed.
Next, the upper half of the GBB kit should separate from the lower half easily for installation. You will see a tab sticking out of the top, and a groove in the charging handle where it mates. This tab is part of the bolt assembly that reciprocates inside of the rifle as it fires, so it is important that the tab and groove are lined up. There is a spring already mounted to the top of the GBB kit, so hook the free end into the charging handle.
Once you have the charging handle onto the upper part of the GBB kit, slide it into the upper receiver of your new rifle. You may need to give it a little push to completely seat into place. Just make sure the front loading nozzle is lined up with the hop up unit before you start applying force. Mine needed a little bit of persuasion, but I didn't need a hammer. The back end will partially stick out of the back of the upper, like in the picture below. This is normal.
Your upper is now complete. Check to make sure the charging handle and bolt move smoothly together, by placing your hand on the back of the upper, and racking the charging handle. The bolt assembly should move about halfway back before it can't be pulled any further. Check to make sure the nozzle is seated into the hop up properly, and that the wheel can turn to adjust the hop up (using only slight adjustments. You do not want to put too much pressure on the bucking.)
Step 7: Remove the Magazine Release and Pistol Grip from the Lower Receiver
This half of the build can get much more complicated. There are a lot of screws and bits and pieces to keep track of. Pay close attention to not lose anything. I will sometimes use small plastic or paper cups and place the screws and parts for each step into one cup, then stack an empty one on top of it for the next set of screws. This way you avoid mixing up screws for different parts, even though they might seem to be the same.
For the first part of this, you will need to remove the magazine release. Again, each rifle is different, but for most AEGs the magazine release is removed by loosening a screw. My G&P had a Phillips head screw. Make sure you keep all of these parts, as they will be used again.
The next step is to remove the motor grip or pistol grip. There are two screws that hold on the motor plate at the bottom. These will most likely be hex screws or Phillips head screws, and are located at the front and rear of the plate. Remove them, and remove the plate. The screw in the middle of the grip is for motor height adjustment, and should not be touched. There might be a small metal disk underneath, so be sure to keep track of it as it is a shim for the motor height adjustment.
You will now have access to the base of the motor. There are two wires, one red and one black, attached to it. On my G&P, there were screws holding the wires in place, but on many AEG rifles they can be pulled off with your finger. Once the wires are off of the motor, slide the motor out of the pistol grip.
The wires will be trailing up through the pistol grip and into the gearbox. If you look into the opening of the grip, you will see some screws holding it on. Use a long shafted screw driver to reach them. Most rifles have two screws, but my G&P had 4. Try not to let them drop into the gearbox opening in the middle though.
After those screws have been removed, slide the pistol grip off the gearbox. The wiring will need to be snaked through the holes.
Step 8: Remove the Buffer Tube and Gearbox Retaining Pin to Remove the Gearbox
Next step is to remove the buffer tube from the back end of the lower receiver. Some AEGs will have wiring inside of the tube, which can make the process slightly more difficult. My G&P was rear wired, so I had to contend with wiring inside of the buffer tube. You will need a long shafted screwdriver (much longer compared to one used on the pistol grip). There will be a screw and a flat nut inside of the tube. You will be reusing this screw, but the kit comes with a different nut to use.
(Old buffer tube retaining nut on the right, new one in the GBB kit on the left)
Next, use a pin punch to knock out the pin that holds the gearbox into the lower. It will be the trigger pin, not the hammer pin (most AEGs have fake ones for the hammer pin. The pin only comes out one way, as it has knurling on one side to make a friction fit into the lower. If you find too much resistance punching it out one way, try hitting it from the other direction. For my G&P, I had to remove it from right to left.
After all of that, the gearbox an be pulled out the top of the lower. Make sure the selector is in the SEMI position to relieve tension on the selector plate.
Step 9: Remove the old selector switch assembly.
For the final preparation for the lower, you need to replace part of the selector switch. As of right now, ambidextrous selector switches are not compatible with the kit. There hasn't been a new release of the kit either, so it doesn't look like it will be compatible in the future.
To remove the switch on the G&P, first you need to knock out the fake side. It is just super glued in place, and I managed to push it out with my own hands. If you need a tool, you could use a pin punch or screw driver as a lever while being careful to not mar up the lower.
Next, use a small screwdriver to remove the left side of the switch. Be sure not to lose the detent and spring however, or else your switch will not lock into place in each position. The screwdriver shaft will need to be small enough to fit through the opening on the right side. You will be reusing the selector itself, the screw, and the detent and spring. The only part you will be replacing is the inside plate.
Step 10: Install the GBB kit selector plate, insert the GBB lower internals, and secure with pin.
Now you need to start back tracking. Installing the lower kit is much easier compared to getting mechbox out. To start, head back to the selector switch. There is a new internal plate to be attached to the selector assembly. Reinstall it the same way the old one was removed, using the screw. There is a semi circular part that mates with the selector, so the alignment is correct. You will know you have it installed correctly when the vertical part of the new plate is in the same direction as the throw lever for the selector. (i.e. if the selector is set to semi, the internal plate should be vertical as well, as pictured). Function check the selector by switching it back and forth between the the three positions. It should move easily, and stay in each position. You may need to adjust the screw to avoid creating too much friction.
Next, slide the lower half of the GBB kit internals into the lower receiver. Make sure the selector is set to semi auto, and make sure the mating selector axle in the lower internals is vertical as well (see picture below). It should just slide right in.
Next, slide the lower half of the GBB kit internals into the lower receiver. Make sure the selector is set to semi auto, and make sure the mating selector axle in the lower internals is vertical as well (see picture below). It should just slide right in.
Line up the retaining pin hole and hammer in the trigger pin that originally held in the mechbox. The pin should be flush with the receiver, or at least even on both sides. Once that pin is in, give it a quick function check. The selector should switch between the three positions and rotate the axle inside of the kit. Also check to make sure that safe works by preventing the trigger from being pulled when the hammer is cocked.
Step 11: Reattach the pistol grip
Flip the lower receiver upside down now, and you will see a Phillips head screw on the bottom of the GBB kit. Remove that screw. The pistol grip will slide onto the bottom of the kit just like it would on a standard mechbox. Use a long shafted screw driver to reattach the screw through the bottom of the pistol grip. It should go through the same hole that the pinion gear would from a motor. Snug it down, but don't over tighten it. The threads are only plastic. You don't need to reattach the bottom motor plate if you don't want to. It isn't required for function. I did just to keep the parts all together.
Step 12: Reattach the Buffer Tube assembly
This step is slightly different than before. Normally, the screw has to be tightened from the tube side. For the kit, the screw goes on the receiver side. Slide all of the buffer tube parts onto the lower, except for the new nut that comes with kit. There will be two tabs sticking up from one side of the nut, that part must go inside of the tube so it faces the receiver. It should align with the back end of the receiver. Tighten the screw to reattach the buffer assembly. I didn't get a chance to snap a picture because it is tough to really see it. Instead, here is a picture from the instructions on Evike's website.
Step 13: Reattach the Magazine Release and any other Odd Pieces.
Lastly, reattach the magazine release. It will go back in the same way it was removed. Slide the L shaped piece from the left side, put the spring on over the threaded post on the right side, and reattach the button onto the post using the screw. At this point, you also want to make sure any extra parts that fell off are reattached. The faux side of the selector will probably need reglued back on. (NOTE: If it has a small slit cut into it, have it pointing vertically upwards or pointed to SEMI if the lower has markings on both sides). Also make sure the faux bolt catch is replaced back into its slot position. Mine fell out when I removed the upper and lower. You can also replace your stock back onto the buffer tube as well (NOTE: If you wanted to change stocks, you don't need to worry about space for a battery since there isn't one. I simply reattached the Crane Stock that came with the gun, but you can opt for another choice if you wanted a lower profile.)
Step 14: Set the Full Auto Disconnector and Reattach the Upper and Lower Receivers
This is the assembly step before your rifle is complete. Just like any other modern rifle, the hammer does not get released for the next shot in full auto until the bolt has nearly made its travel back into battery (all the way forward). The M4 or M16 has this sear in the rear section of the lower. Since the GHK's bolt is only half the size, the auto sear is in the front. If you look at the assembly instructions, it shows the sear being tripped to allow the hammer into the correct position to begin shooting. If you don't set the sear, then you could have problems with your hammer.
All you have to do is press it forward towards the magwell. It is that simple. The pictures below can illustrate the difference.
NOTE: You will need to set the auto sear EVERY time you remove the upper from the lower.
Pictured is the hammer is being held back by the auto sear (tab sticking up vertically)
Pictured is the auto sear in the correct position, ready for assembly
Step 15: Reattach your Upper Receiver to your Lower Receiver
Reverse what you did for Step #2. You need to slide the upper onto the lower so the part sticking out of the back can fit into the front part of the buffer tube. The pin holes should line up. Both pins on my rifle lined up great, and I only needed finger pressure to reattach the pins.
Next, perform a basic function check to ensure everything has been mated up properly. If you don't know how to perform a function check, it is simple to do.
1) Check to make sure the safety locks into each of its positions.
2) Set rifle to SAFE, pull the trigger. There should be little to no movement in the trigger, and the hammer should not drop.
3) Set the rifle to SEMI. Pull the trigger and hold it to the rear. Rack the bolt with the charging handle and slowly release the trigger. There should be an audible 'click'. If you pull the trigger again, the hammer should drop again. Rack the bolt again.
4) Set the rifle to AUTO. Pull the trigger and hold it to the rear. Rack the bolt a few times, roughly 3-5, while still holding the trigger. When you release the trigger, there should NOT be an audible click and the if you try to pull the trigger again nothing should happen. With the trigger released, rack the bolt. This should reset the trigger and hammer, and allow the hammer to fall if the trigger is pulled again.
5) With the trigger released, rack the bolt and set the rifle to SAFE. Your function check is now complete!
Final Thoughts:
Now you can gas up your rifle and head out to give it a test fire and set the hop up. If you have any optics mounted, you might need to re-zero them as well. My pending review for this rifle will cover more of the function and performance.
I will give you a small preview though. The GHK mags are spec'd for an AEG magwell, so my ICS Redi-Mag holds the GHK GBB kit mags perfectly.
Stay tuned for the full write up!
