Taken from the now defunct
www.airsoftplayers.com.
The Spring/Bushing UpgradeThis tutorial starts assuming you have already worked down to the mechbox (gearbox). If you need information on removing the mechbox from the rest of the gun, you should consult your owner's manual and try to use the supplied diagram. Some guns are easier than others, so just take your time. This is also for the version 2 mechbox. Most all guns sold today come with version 2 or version 3- I will try and make comments where appropriate regarding any differences in version 3.
This tutorial only breaks the mechbox down, installs new bushings and a new spring, and then reassembles the mechbox. It is on the assumption that you are starting with a stock gun. It will also be helpful for just answering the general questions "How do I get into the mechbox."
Supplies- in order to work on a mechbox, you will need medium to very small Phillips screwdrivers, a #10 Torx driver, a straight slot screwdriver, and some lube. You should consult the FAQ to read up some on the different options for lubing the mechanism, but in this tutorial I will use the same that I always do: For the piston and cylinder, Lube Gel from Radio Shack. For the gears, standard white lithium grease. You will also need a razor sharp cutting instrument. You should try to have a clean surface to work on, preferable a light color so the components stand out easily once you remove them. You should also have a rag of some sort for wiping your hands and components.
Version 3 mechbox note: on a version 3 mechbox, you will have to first remove the assembly that holds the motor onto the mechbox. Do that. Then remove the metal plate that is on top of the mechbox. It should slide off, sliding towards the front of the mechbox- it may be difficult the first time sliding it off. This plate houses the hopup cover assembly on the AUG, and the spring loaded cover button assembly on the AK. AUG: There will also be 2 wires, the contacts for the trigger, being held in place by plastic. You need to also remove that assembly. There are two screws on the assembly- one that clamps the wires down, and one that holds the whole assembly onto the mechbox. Only unscrew the one that holds the whole assembly down (the larger one) and you will have a MUCH easier time reassembling the box. AK47: The AK has a very clever firing mode selector switch mechanism. Just slowly take it apart, paying attention to how the gears interact on the outside of the gun. Remove the entire selector switch assembly before continuing. BOTH: There is also a black piece of plastic behind the trigger, which guards one of the gears. Be sure to remove that as well. It just pulls right out.
The first step is to loosen the 4 Phillips screws on the mechbox. You need to be very careful in remembering which screw goes where- this holds true for all eight screws that hold the mechbox together. They are of different lengths, and only some have washers. Some people place the screws in a pattern that matches their location on the mechbox. After the four Phillips, take out the four Torx screws. These screws are marked by a 'T' in the picture below. These should be removed so that the first one taken out is by the nozzle, and the last one is by the back of the mechbox, since that is where the pressure exerted by the spring is the greatest. Overall, remember the mechbox will be under some pressure the whole time it is assembled. While I have never had one burst apart on me, even after all screws have been removed, it is still a good idea to keep the two halves pressed together until you are ready to take them apart.
Outside of the mechbox, Torx screws marked.[/b]
Once all screws have been removed, you are ready to pry the box apart. To start this, take the straight slot screwdriver, and find one of the openings in between the two halves (the motor opening, the trigger opening) and gently start prying the case apart. As soon as you have the two halves starting to separate, you need to take an extra, small screwdriver and insert in into the whole in the back on the mechbox. This is the spring guide, Once the screwdriver is in, you need to push downwards on the front of the screwdriver- this is to keep the spring in check while you open the mechbox. See the picture below. This is the part of the process where a second set of hands would be extremely helpful. (
Version 3 note: the version 3 mechbox may not have the whole on the back, going to the spring guide. If this is the case, you need to pry the mechbox apart anyway, and just insert a screwdriver as described above as SOON as you can, and before fully prying the mechbox apart.) Once you have the spring guide secured, then you should try and also press down on the top of the cylinder, and then proceed with separating the mechbox. There may be a point where there will be a popping sound as the guts of the mechbox loosen finally.
Securing the spring guide with a screwdriver.At this point, here is what you must watch out for: the shims on the gears. The shims are VERY thin washers on the gear axles. When you first pop open the mechbox, depending on how much the gun was used prior to the upgrade, you need to be mindful of the shims. The shims will either stay on the axles, come off with the bushings, or simply pop off into the inside of the mechbox. The bushings are the three pieces of plastic in each half that the axles fit into and spin inside of. The picture below shows a shim resting on one of the bushings. The gun in the picture was fired about 70 total times before the upgrade took place, so there is minimal wear. Once the top half is removed, immediately inspect for any shims that have been popped free. Take note of where you think they came from. Next, inspect the top half for any shims stuck on the surface of the three bushings. Sometimes they will be hard to spot- they can look just like the bushing surface. So carefully examine the inside surfaces of the bushings and the area around them. If you find any shims, place them back on the axel on which they belong- and leave them there.
A shim still on the mechbox bushing. On highly used guns, this wont be so easy to spot.[/b]
First order of business is removing the spring. While still maintaining control, gently lift up on the spring guide that the screwdriver had been inserted into. It will lift straight up. Upon lifting it, allow the spring to relax. This will relieve all pressure in the mechbox. The first picture below shows you what the mechbox should now look like, withe the spring still intact but with the spring guide liften out. Then gently pull on the spring, and pull the piston out from inside the cylinder. The spring is fixed to the piston, so it will come out with the spring. Then just place the spring/cylinder assembly to the side. Next, remove the cylinder/tappet plate. There is a spring that maintains resistance on the tappet plate that must be removed. Keep a finger on top of the spring so it doesn't fly off, and then lift the spring off the metal post on the mechbox, using a small driver of some sort. This is shown in the second picture below. Once lifted off, you can lift out the entire cylinder and tappet plate assembly. This should be done by pulling up on the cylinder, and rotating the top of it towards you as you pull. Place that assembly to the side as well.
The mechbox internals, once the top half is removed.Lifting the tappet plate spring. Keep your finger on the spring so it doesnt fly off.You can now start removing the gears. Start with the gear at the bottom of the mechbox, the bevel gear. This is the gear that meshes directly with the motor. When you lift it up, look for any shims that may be on the bushing underneath it. Remember, keep all shims on the gears. Place this gear to the side. Revealed under the bevel gear is the anti-reversal latch. Just take note how this latch goes in, and how the spring is mounted, and it will be very easy to put back. The position is illustrated in the picture below. Next, lift out the top most gear, the sector gear. This is the one that meshes with the piston. Again, look for shims underneath the gear, on or around the bushing. Finally, the spur gear is lifted out. This gear simply transfers power from the motor to the piston. Again mindful of shims.
Position of the anti-reversal latch, with the bevel gear removed.
Note: The anti-reversal latch does NOT end up in this position. It ends up
resting against the bevel gear, not the spur gear shown above. This picture
is to only show the spring placement.[/b]
At this point, the all you really need to do is remove the plastic bushings in the bottom half. However, the selector plate on the back of the mechbox stops you from getting to one of the bushings. You can certainly try to lift the bushings out of the gun as it- just hold the remaining components in place- especially the trigger mechanism, and with an instrument of your choice, pull out the bushings. If the gun has been fired much, or just if the bushings are in there well, this will NOT work. So you must simply continue disassembling until you can get to the bushings from the backside. This is what this tutorial will do now.
Examine the back of the bottom half, where the selector plate is- you will see a small spring applying tension, and the black safety lever that is moved by the plate itself. You can see both of these is the picture below, and both need to come off. First the spring- be VERY careful. The spring is very small, but is easy to remove. Again, place a finger on top of the spring to stop it from flying off, and then simply pull back on one of the ends of the spring with a small screwdriver. Just take your time, and it shouldn't fly off. Turn the mechbox half back over so you are once again looking at the inside. There is a Phillips screw holding in the black lever in place. This is the screw on the right in the second picture below. Take out that screw, and then pry off the top arm. Pay close attention to the spring and how it is placed. Lift off the spring, and then you can pull the lever out from the bottom side. There is a metal lever that needs to be removed- it is what the small spring was pressing against. There is a single screw holding it down. This is the screw on the left in the second picture below. Just remove the screw, and then take the lever out. It may take some twisting and turning to remove the lever- it is fitted in there fairly well. Just keep your thumb on the trigger assembly while removing the metal lever. Now once again flip the mechbox half over, and now you can slide out the selector plate. This clears up the space behind the bushings.
Back of the mechbox/selector plateClose up of safety lever and the other piece that must be removed to get the selector plate off.Now you need to remove the plastic bushings. The easiest way is to take a screwdriver slightly larger than the opening in the bushings, and push on them from the bottom side. When doing this, be sure to keep your thumb on the trigger mechanism so it doesn't come undone. Some bushings will come out easier than others.
At this point, you have basically removed everything that needs to come out of the mechbox. The picture below shows every part that should be removed. The order from top to bottom, left to right is the cylinder/tappet plate, spring guide/spring/piston, anti-reversal latch, bevel gear, sector gear, spur gear, very small spring from selector plate, metal arm and screw that very small spring connects onto, 3 pieces of the safety arm assemble, the selector plate, and the 6 plastic bushings.
All parts removed from the mechbox.[/b]
Once the bushings are out, put the mechbox aside, and lets turn our attention back to the spring and piston. The piston head is screwed onto the piston, and catches a metal spacer inside the piston that holds down the spring. The problem is that the piston head is covered in plastic, and the screw is inside of it. I recommend NOT trying to simply grab the piston head and unscrew it out of the metal- you don't want to risk ruining the round shape of the piston head. Instead, take a very sharp cutting tool, and start carving out the center of the piston. This is shown in the first picture below. This slowly will reveal the screw underneath. Once the head of the Phillips screw is revealed, as shown in the second picture below, use a screwdriver to unscrew the piston head from the piston. The O-ring behind the piston head will come loose real fast- just leave it clinging to the piston head itself. (Note: the piston head found in this tutorial, taken from a brand new Tokyo Marui XM177E2, is different from all others that I have worked on. The O-ring has plastic above it and below it. Looks much more secure.)
The screw head revealed. Sorry about the fuzziness.Once the piston head is freed from the piston, with screw intact, the spring will pull right out of the piston body. Now, officially, the reassembly begins. First, wipe all grease off the O-ring and piston head. Next reattach the piston head to the piston- you will need to reinsert the metal spacer back into the piston- there is a metal nub sticking out of it that goes into a corresponding hole inside the piston. Get that lined up, insert the metal spacer, spin it inside the piston with a screwdriver until the nub is in the hole. Then, take your old spring, and insert the flat end back into the piston- this is only to apply pressure to the spacer. Then start screwing the piston head back on, until it is tight. Remove the old spring- it wont be needed anymore. Take out the new spring- the PDI line comes with plastic washers- place one in the piston on top of the spacer. You can now place the spring assembly to the side once again. (UPDATE: RK00 recommends instead of cutting out the piston head, getting a pair of pliers and gently unscrewing the whole piston head off from the piston. This will work, IF you are VERY careful not to warp the round profile of the piston head. If the head is somewhat flattened and no longer round, you will lose a proper seal with the cylinder, and your compression will be shot, and your fps will fall. Also, I will also point out that on one occasion, I have had the screw head, buried in the piston head, actually break free of the plastic surrounding it, so that it was spinning freely inside the piston head. This is rare, but bad if it happens. Using pliers would increase the risk of this taking place.)
Back to the bottom half of the mechbox. Next the selector plate goes back on. Insert the plate back into the slots for it, and then reattach the black level, simply reversing the steps from before. Install the bottom half of the lever from the bottom, put on the spring, put the top half back on, and then put the screw back in. The top of the black lever will only go on one way, so it doesn't take any guessing. Once the lever is reinstalled, reinstall the metal arm. Then put the small spring on the back on the selector plate back in place.
Flip the mechbox back over. Wipe off any grease that is left, both in the piston groove and by where the gears go. Once clean, you can insert the metal bushings into the three holes. Push them down firm, but do not use any metal instruments to apply force- you do NOT want to warp or bend the inner rim of the bushings in any way. Now it is time to put the gears back in. First is the spur gear. Apply some grease (in my case, the white lithium grease) to the opening in the bushing, illustrated in the picture below. Also apply some to the shim and the axel itself. Place the gear back down into the bushings. It should rotate fairly easily, with minimal resistance. Next is the bevel gear. You must first put the anti-reversal latch back into place. Clean the latch off of old grease, apply new grease, and then reinsert into its receptacle. Make sure the spring is positioned correctly. Apply grease to the top surfaces of the spur gear. You may choose to wipe off the old grease from it as well. Now apply grease to the bushing and gear axle, and drop the bevel gear into place so it meshes with the spur gear.
Lubing the metal bushing with what lithium grease.[/b]
Now you should be able to turn the bevel gear freely counterclockwise, and it will turn the spur gear as well. This is the direction it spins when in operation. Turning the bevel gear clockwise should cause the gears to stop turning once it hits the anti-reversal latch. Turn the bevel gear until this does happen- until it stops turning- and leave the gears in that position. Finally, lube up and insert the sector gear. HERE is the gear timing- with the bevel and spur gear in the position described above, so that the gears cannot be reversed any further, the sector gear is inserted so that the metal column sticking out of the top gear surface, the one that the tappet plate interacts with, is in the one o'clock position. See the picture below for more clarity on this.
After the bevel/spur gears are rotated backwards until stopped by the anti-reversal latch, insert the sector gear as shown above.Now the cylinder goes back in. Insert it using the opposite motion that was used to remove it. Once in place, reattach the spring. The end of the tappet place should rest up against the axel of the sector gear. You should apply lube (in my case, the Lube Gel) around the head of the piston- be sure to hit the whole O-ring. Also apply some to the 2 grooves along the side of the piston. Now insert the piston back into the cylinder, with the new spring in place. Make sure the slots on the side of the piston line up properly with the grooves in the mechbox. The springs all have one end that has the coils more tightly wound- that is the end that goes IN the piston. DO NOT compress the spring and put the spring guide in place yet.
In order to test the compression of the cylinder, put your finger over the end of the nozzle, pull out the piston until the piston head is just inside the cylinder, and then try and push the piston back in. The piston head should form a tight seal with the cylinder, and the piston should not be able to be pushed all of the way forward with your finger on the nozzle. If it can move easily forward, you need to check the piston head and make sure it was reassembled correctly. Also check and make sure that when you move the tappet plate, the nozzle moves as well. The tappet plate locks into the nozzle, as shown in the picture below, and if it become separated, you can still easily reassemble the mechbox, but it wont chamber the bbs correctly when you fire the gun.
Picture of the tappet plate (black plastic piece on the bottom) interacts with the nozzle (black plastic piece extending to the right).[/b]
Now, here is one of my little tricks- apply grease to the tops of the axels of the gears, and then go ahead and put on the metal bushings- remember to put them on so that the fatter side is down. This will make it MUCH easier to put the top half of the mechbox back on. Make sure the bushing on the sector gear is on TOP of the arm of the tappet plate. It should look like the picture below.
Bushings, lubed, placed back on the axles of the gears.Take the top half of the mechbox, and wipe it clean of all grease. Then in the groove for the piston, apply new grease. Apply a small amount of grease to the top of the anti-reversal latch as well.
You are now ready to put the mechbox back together. First, compress the spring and reinsert the spring guide back into position. The piston should be all of the way inside of the cylinder. The spring guide has two tabs on the back of it, and they go up and down directly into the mechbox halves. Reinsert the screwdriver into the back of the spring guide and apply pressure in the same manner that was done when taking the mechbox apart. Again, here a second set of hands would be most helpful. Start to place the top mechbox half back onto the bottom half. Once aligned, use one of your fingers, going through the cylinder opening in the mechbox, to hold the cylinder in position. Then try to further put the top half into position.
There are 5 things to look for when doing this: each of the three bushings must be centered in their holes, the anti-reversal latch must go into its hole, and the black lever (which is the safety for the gun) must be actually inside the mechbox. Due to the spring tension on that lever, it may be rotated down some, stopping the mechbox halves from meeting. Try to fully close the front (nozzle end) of the mechbox first. Check the black safety lever, and make sure it is pushed up inside the mechbox. Next, using as screwdriver, from the outside, check each of the bushings, and adjust them slightly so that they are in their holes. Finally, you may have to move the anti-reversal latch some to get it to get in its proper place.
At this point, the mechbox should be able to be fully closed. You can also remove the screwdriver and stop applying pressure on the spring guide. If the mechbox has not fully closed- if there are still any gaps between the two halves- then check the following, in this order:
1. Anti-reversal latch
2. Each of the gear bushings
3. The black safety lever.
If those are okay, then you will have to reopen the mechbox after reapplying pressure with a screwdriver in the spring guide. Then look for
4. The trigger assembly. Make sure it is laying flat.
5. The tappet plate arm. Make sure it is under the sector gear bushing
6. The cylinder head. There is a hole in the head that part of the mechbox goes into.
7. Spring guide. Make sure the tab is facing straight up.
8. Bushings. Make sure they are all of the way down.
Also make sure that the wider end of the bushing is down. If all of that checks out okay, then reattempt to seat the top half. If it still doesn't work, then disassemble the gears, and start over. Otherwise, you should now just reinstall the 8 screws, in the reverse order they were removed. Do the four Torx first, starting with the end closest to the back of the mechbox, and then working your way forward. Then the four Phillips screws. The trigger should be able to be pulled just as if it was back in the gun, and by sliding the selector plate on the backside of the mechbox, you should be able to make it so the gun is in safety, and the trigger cannot be pulled. If everything feels okay, then just reinstall the mechbox back into the gun, and you are good to go.
All photos and text ©2001 Airsoftplayers.com.