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http://www.airsoftretreat.com/reviews/showproduct.php?product=67&title=-how-to-3a-a-guide-to-your-mechbox&cat=49

By popnfresh wLcH

First, to even get to the mechbox, you will need to strip your gun completely so you can dislodge the mechbox from the gun’s body. This usually means removing the pistol grip, a few pins, a few miscellaneous parts, and sometimes, the stock. Once the mechbox is dislodged from the body, you will notice several distinct sections of the mechbox, and what they contain is good to know before you open the thing up so you don’t have a spring guide flying across the room.

The orientation of the screws on your mechbox is slightly different than those of the V2 and V3. Aside from having 5 screws like the CA mechbox, the order of Torx and Phillips head screws are as follows: Phillips, Phillips, Torx, Torx, Torx. The second Phillips head screw holds the lower wiring assembly to the mechbox.

The back of the cylinder head is home to small hole and a black, rubber surface which absorbs the impact from the piston head. The small hole on the back of the cylinder head is the first step in channeling the air for “export” down the barrel. On the front end of the cylinder head is a small protrusion where the air nozzle is placed.

This picture contains both the cylinder and the cylinder head.

This picture contains both the air nozzle and tappet plate.

The sector gear is the gear that directly engages the piston, and is the final step in creating the amount of torque necessary to pull back the spring. It has a large, and clearly defined rack of the teeth that engage the piston, and a small rack on the underside that engage the spur gear. It also has a small nub on the inside of the first, larger rack that engages the tappet plate and allows it to function. There is also a small egg-shaped nub on the underside of the sector gear, which engages the cut-off lever, which is necessary to retain proper semi-auto function.

=== IIj. The Anti-Reversal Latch: ===

The cut-off lever's position is marked.

=== IIn. The Trigger Assembly: ===

Although it resides on the outside of a V2/V3 mechbox, the selector plate is the heart of controlling firing modes. It pushes on contacts on the inside of the mechbox, and depending on where it’s positioned, can also determine whether the cut-off lever works properly or not.

Second, as you remove the screws around the mechbox, be sure to lay them out on a flat surface like a diagram, noting where all the screws are supposed to reside. If there were any washers on any of the screws, be sure you place them on the correct screw, and place them in your “screw map.” It will be essential to the box’s integrity to have the correct length screws for their respective holes.

Now is the time where an extra set of hands can be VERY helpful. If you don’t have another person to help you, be sure that you can secure both the cylinder and spring guide before you completely open the box. When you’re ready, remove the last screw, keeping the gearbox closed tightly, and place it in your screw map. Now secure the cylinder with your hand, and open the box VERY slightly, just enough to place a screwdriver in the spring guide’s hole. Then, very slowly, begin prying the gearbox apart, making sure to keep the cylinder and spring guide firmly secured. When you have enough room, let the spring guide out of the mechbox along with the spring, and remove the upper shell of the mechbox.

Now you see the big jumble known as the “hell-hole” in front of you. Congratulations, you have successfully opened up your mechbox without hurting anyone in the general vicinity!

For a large labeled version of this pic, [go to the original article and] click here.

Second, you’re going to want to remove the tappet plate and cylinder unit from the mechbox. On the underside of the tappet plate is a small spring that is connected to a nub on the mechbox shell. Very carefully, take this spring out with a thin screwdriver or something of that nature, and do not lose it! Set the tappet plate aside along with the nozzle, cylinder, and the tappet plate spring for later.