This document was originally published on "Airgun Custom Parts Catalog '98" by Seibido Mook in Japan. It has been translated by Francis Zhou (Skyfire) at his spare time. Since the translator wasn't a Japanese native speaker, please be adviced that the content of this document may not completely reflect that of the original.

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Tokyo Marui AEG Mechbox Ver 3 Disassembly Instructions

1) Tokyo Marui makes 4 types of mech boxes for it's AEGs (now five including the UZI), the one shown in the picture to the left is version 3. The basic dis-assembly steps for all mech box is the same, so after going through the process for version 3, you should be able to open other versions accordingly. The motor shown at the bottom is the EG700 high torque model.

2) Start by using a screw driver to pry out the cover piece at the top of the mech box. There is a small lock (?), so be careful. The driver used here should be a fair sized one, since a small driver can be broken if enough force is applied.

3) Now use a pair of pliers to pull the cover plate off. Don't worry, you won't warp the cover plate, just be careful not to cut your fingers.

4) If you look at the right side of the gear box, you should see three connectors. While dis-assemblying, be careful not to cut yourself on them.

5) In order to open the gear box, pull out the connector cords and loosn the screws. The parts that hold the wires are fairly fragile, so handle with care.

6) Take out the two bottom screws first and remember which hole the screws go in. No matter which mech box you are working with, this is the basics.

7) After taken out the two bottom screws, the bottom pieces can be taken off.

8) The mech box uses a special type of screw, it's better to take them out using a touque wrench. Torque wrench is a neccessary item for taking apart gear boxes.

9) Take out the screws that holds together the mech box one by one.

10) This is what everything should look like before finally separating the two pieces. Remember to get the washers with the screws as well. A small magnet should come in handy for such jobs.

11) Now use a screw driver to pry open the box. Use your finger to press down on the cylinder to prevent the spring from buckling out.

12) It's usually preferable to take the right half of the mech box (left part in the picture) away from the left half. Be careful since the spring may fly out and the parts might be lost. To be safe, operate in a large, clear plastic bag.

13) This is what the inside of the mech box look like. Remember the layout, so you can refer to it when installing custom parts.

14) First, take out the spring guide carefully, and let the spring relax.

15) Now take out the spring, which is attached to the piston. There is a lot of grease on the spring, it's neccessary for the smooth operation of the gun.

16) Next thing to take out is the tappet plate. When taking out the tappet plate spring, be careful and don't let it fly out.

17) Take the cylinder and tappet plate out together. There aren't any loose parts so don't worry.

18) Now you can separate the tappet plate and the cylinder. Pull the tappet plate forward a bit and it should come off nicely.

19) The air nozzle is only clipped to the tappet plate, so just take it off. These are many custom replacements for the nozzle, choose the one that best suits your purpose. Installation of this part is very straight forward

20) Now the cylinder and cylinder head can be separated. These is more grease on both inside and outside of the cylinder, so think about where to place it. Many custom parts can be found for these items, so you can choose freely and make your custom gun. When you install custom cylinder/head, make sure you spread the inside with high viscosity silicon grease (Z-shot, the company which makes Systema parts, also makes the grease).

21) Now that all air piston related parts are gone, gears are the next thing to take out. Start with the top most bevel gear. This gear only sits on top of other parts, so simply hold pull it up.

22) This is where the sector gear should come out. This gear is where the energy created by the motor is finally delivered to the piston. If you want to replace it with custom parts, make sure you also replace the piston with the one that fits this gear.

23) The small part (helf by two fingers) shown is the reversal stop latch. If this part is not present, many parts might get damanged by the reversed rotation of the gears due to spring movement. Absolutely don't forget it when putting everything back together.

24) After taking out the spur gear, dis-assembly is basically complete. It's not all that difficult, the only part that might be hard to remember is the relationship between the gears. Of course, you can always refer to figure 13 if you forgot where everything goes.

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25)26) In order to take out the trigger switch, the spring has to come out first.

27) Now simply pull the trigger switch out. Triggers on normal airgusn are mechanical units which transmits force and releases the piston, but in the case of AEGs, it's only an electric switch. Thus, it's light weighted, also it's possible to change the trigger pull pressure. Just another potential and charm of AEGs.

28) In case of AEG malfunction, if firing on semi-auto didn't solve the problem, then it could be a problem with bad connection, especially in the trigger switch. If it's impossible to fix, bring the mech box to the local shop and ask for professional help.

29) Before taking out the trigger, make sure you've confirmed the position of the trigger spring. Usually, the end of the spring that faces the trigger is longer, while the end that faces the mech box is shorter.

30) Now the tigger can also be pulled out. As of now, all major components have been removed. But there are still more minor parts left.

31) The trigger still has a shear (spelling?) which can be pulled out horizontally.

32) There is a spring attached to the top of the trigger.

33) This is the cut off lever for semi-auto firing. This part by itself is no problem, but upon re-assembly, over tightening the screw can prevent this lever from functioning correctly, so be careful.

34) This is the selector lever on the side of the gear box.

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35)36) This part is simply snapped on, so just take it off. From here there are no more big parts, so decide where you want to place the rest of the items.

37) A pincer would be best for taking out this spring.

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38)39) Loosen up the screw and take out the cut off lever. The warning about this item has been said before, see step 33.

40) To take out the bushings, simply use a precision screw driver and a plastic hammer to knock them off.

41) These three gears moves the most in an AEG. There are many custom replacements for them, choose the ones that best fit you need. When re-assemblying, remember to apply grease on them. If you don't use an approapriate amount of grease, the gun may not perform at it's fullest potential. The places and numbers of sims needed differs for gear box to gear box, so remember it well. As of Mech box ver3, there are two 0.3mm sim under the section gear, one 0.5mm each above and below the spur gear, and one 0.3mm below and one 0.15mm above the bevel gear. (lay the left side of the gear box flat on the table top, the closer side is top and the other side is bottom)

42) Cylinder related parts affects power, range and stability the most. Inapproapriate replacements can damange the rest of the parts. Therefore, select the custom parts that best fits your purpose.

43) This picture shows the completely disassembled mech box parts. Tokyo Marui makes several versions of this box, but the basic design is the same. Use this document as a reference and dis-assemble your favorite AEG as you like. After installing custom parts, if you perform regular maintanance, the gun should work nicely everytime you shoot it.

Written by Francis Zhou, 10/28/98.