Jump to content

to add your 300x250 banner, pay ad zone 5
Airsoft Atlanta is your source for quality airsoft guns and rifle parts
to add your Text Link here, pay ad zone 3

AirsoftAtlanta.com AirsoftNMore.com Airsplat.com AirsoftRC.com
Vote for us to add your 180x30 banner here, pay ad zone 2

If you appreciate this website, please ASF Donation or Check Out the ASF Store. If you can not help us financially,
then at least help us by telling a friend: Share us on your favorite social networking website Bookmark and Share

Important Announcement!

Our Pinzgauer Project is in "Pre Launch" - Click Here to let us know what you think before the project goes live.

* * * * * 2 votes

G&G Umg Field-stripping And Version 3 Mechbox Disassembly

  • Please log in to reply
17 replies to this topic



    The New Guy on the Block isn't so new anymore...

  • Forum Administrator
  • 6,855 posts
  • Gender:Male
  • Location:Fairfax Station, Northern Virginia
  • Interests:I love to drive and work on SAAB cars<br /><br />Alumni of the Thomas Jefferson High School for Science and Technology **RANKED BEST HIGH SCHOOL IN THE US BY USNEWS**<br /><br />Undergraduate Industrial Systems Engineering at the Virginia Polytechnic Institute

Posted 25 January 2007 - 12:09 PM

Internal Troubleshooting of the UMG

A Disassembly and Parts Guide to the Guay & Guay UMG and Version 3 Mechboxes

The repair and upgrade of almost any internal mechanical apparatus requires an almost, if not full, disassembly of the components to its individual parts. The Guay & Guay UMG is no exception.
G&G has simplified the field-stripping process in their UMG model, which greatly increases the speed of take-down and simplifies the process for those who are not as mechanically proficient. However, the disassembly of the gearbox and its components may prove to be a more daunting task. The purpose of this article is to break down the process from step one.

*Note: Pictures from my articles will no longer have on-page illustration; instead, I will now have links to photographs. This will save you download time, allowing you to see photos in larger detail without the wait and prevent the post from being twenty-five web-pages long.*

Firstly, you need to remove a pin located under the stock retaining button. The pin’s open head should be facing toward the left side of the gun (with the stock towards the user). Applying some force into the pin on the left side should be able to push the pin through the right side of the UMG, where it can be pulled completely out. Careful when pushing it with a finger; the metal coil inside the pin can pinch!

Field-stripping Pin

Next, you need to reach into the magazine well. The magazine well is located in front of the trigger guard and allows a secure hold onto the UMG magazines. A metal hop-up chamber is located at the top of the magazine well. With one finger, push the hop-up chamber towards the barrel. A spring keeps tension on the hop-up chamber away from the barrel, so one needs to apply constant force. Keeping the hop-up chamber pushed towards the muzzle of the gun, slowly pull the lower receiver downwards. The lower receiver consists of the grip, magazine well, trigger, and trigger guard. It is crucial that you keep the hop-up chamber pushed against the barrel; pulling down on the lower receiver without pushing the hop-up chamber will cause possible damage to the cylinder, tappet plate, air nozzle, hop-up chamber, and/or the barrel. The lower receiver should begin to swing smoothly downward. You can now remove your finger from the hop-up chamber.

Hop-up in Magazine Well

Let the lower receiver swing completely downward so that it is almost perpendicular to the upper receiver of the UMG, which consists of the upper body, the rails, the stock, the foregrip, and the outer barrel. You then need to pull the receiver backwards. There is a pair of “hooks” that latch onto a pair of “nubs.” The nubs are located on the foregrip of the upper receiver and the hooks are located at the end of the lower receiver. Remove the lower receiver so that the hooks become unattached from the nubs. The top part of the gearbox should be exposed at the top of the lower receiver.

Seperation of Lower and Upper Receivers

Inside the upper receiver, you will notice the hop-up chamber and part of the brass inner barrel exposed. Before removal, the barrel assembly must be twisted clockwise, or away from the user. The barrel assembly might spring out, as there is a spring that keeps the barrel assembly under pressure. You can then pull the entire unit out from the outer barrel.

Removal of Hop-up and Inner Barrel

At this point, the UMG should be in three pieces: the lower receiver and gearbox, the upper receiver, and the barrel assembly.
Set aside the upper receiver and the barrel assembly, as they are not needed in the disassembly of the gearbox.
If you desire to install the custom UMG-type 9.6v battery, you may find that removing the battery compartment door would help to create more room for the extra battery cells and wiring. The battery compartment door is not secured by screws or welding. A simple pull of the entire back section of the battery compartment door should be enough to ease it through the back of the upper receiver. Push forward initially, then ease through the opening at the back of the receiver. Do not use excessive force, but some adjustment and wriggling may be necessary to pull the pack battery compartment door out. This creates more than enough room for the extra battery cells. It is highly recommended that you use the custom UMG-type 9.6v battery. You will notice a significant difference in motor cycle speed, compression cycle speed, and rate of fire. What I recommend doing is removing the pin from the battery compartment door and removing the hinge so that the lower section of the compartment door can be reattached. This leads to a more stable structure in the rear of the gun and prevents some flexing and rattling.

Removed Battery Compartment Door and Battery


*Note: Parts of the gearbox seen in photographs from this guide are NOT original, but illustrate the text nonetheless. The parts are from a slightly modified Hurricane G36C full tune-up kit.*

*Note: The gearbox shown in the following photographs have been cleaned and all debris and grease has been removed in order for a clearer view of the internals.*

Before embarking on the task of disassembling the gearbox, please consider the following recommendations:

1. Set up a large, brightly lit area that is not located on an expensive table, antique furniture, white carpets, etc.
2. Place an old white towel on your working area
3. Print out a picture of the internals of the UMG and the gearbox of the UMG from the Guay and Guay website
Guay & Guay Website

One will need the following tools and accessories for a complete disassembly of the UMG gearbox:

1. Set of Allen wrenches in the metric system
2. White lithium grease (not the spray type)
3. Small towel or rag
4. Cotton swabs or Q-tips
5. Set of screwdrivers, both flat-head and Phillips
6. Pliers
7. Find a stack of Post-It notes or notecards
8. Find a dark-writing pen
9. Optional: rod of dense plastic or metal 6mm in diameter (you can even use a BB)
10. Rubber mallet (steel hammers are not recommended, but if no rubber mallet is available, be sure to take care in using a steel hammer)
11. Brush
12. Optional: digital camera

Old grease can possibly stain a working area surface, so a towel that you can afford to get dirty is highly recommended to cover the surface. If the towel is white, you can locate lost parts easier. Work in a well-lighted area that will keep the space illuminated. A larger work space will allow the parts and tools to be spread out; having pieces and parts on top of another in a pile will make the task much harder.
Print out pictures of the UMG internals and of the gearbox components. Having visual guides helps tremendously in disassembling the UMG.
The notecards or Post-It notes and the pen are to help in keeping the individual components in check. Having a labeling system helps in preventing a situation where you do not know where a random piece goes. As soon as a part is removed, give the part a number and mark it on the visual aids, then write the same number on the Post-it and place the part on top of it.
I found that periodically taking a photo throughout my disassembly saved many a lost or random piece. I was able to refer to the stock factory arrangement of the internals of the gearbox. I recommend the use of a camera especially to new users and first-time dissemblers. After multiple disassemblies, the process is committed to memory and becomes significantly easier. The more times you take apart the gun and gearbox, the easier the process becomes.
The first step in removing the gearbox from the lower receiver is releasing the motor cage unit from the grip. Three screws are located at the bottom of the grip, two of which are the same size and one which is of a slightly larger size. Remove the screws. Label one notecard or Post-It with “grip screws” and place the screws on the paper. You can remove the bottom grip plate, but the step is not completely necessary. The bottom grip plate can stay in its slot at the base of the grip.
On the sides of the lower receiver are a set of what looks like a series of pins. Be warned, only one of these pins actually comes out! DO NOT try hammering out all the pins! The pin that should come out is the first pin from the magazine well. A sharp tap with the mallet and a small Allen wrench should pop the pin out.

Gearbox Pin

The gearbox is now “floating” in the lower receiver and can be removed. However, as the gearbox is pulled out, it is necessary to adjust the selector plate switch to allow the gearbox to pass through the lower receiver. Keep on switching between the different modes that seem fit. The grooves for the selector plate interfere with the selector switch as it is pulled out; adjusting the selector switch will allow the gearbox to be pulled out. Do not yank the gearbox out forcefully; it should slide out relatively easily. If it does not, be sure to check for one of the grip screws still in the grip or play around with the selector switch more. As the gearbox slides out, be careful of the wires so that they aren’t stretched or broken.

Gearbox Removed

At this point, the gearbox should be separated from the gearbox. If you are using a camera, take a quick snapshot of the gearbox on either side. The selector switch assembly can be slightly tricky to reassemble later and pictures can aid in remembering the setup. We will now designate the left side of the gearbox as the side with the switch assembly and the right side the shell with a metal side plate mounted to it.
Place the gearbox on its left side. The side with the wires should be against the work surface. The visual guides and disassembly process was based with the disassembly of the gearbox from the right side. Using the “label-and-place” system, remove the two screws that hold the motor cage unit to the gearbox and the four screws that hold the gearbox halves together while keeping a hand pressed down on the right side of the gearbox. Note how the wires of the motor are arranged (with the use of a camera if possible) and place the motor away from the tools and the gearbox. The motor has a strong magnetic force and metal tools will be attracted to it. Avoid having tools scrape against the motor. Most of the gearbox screws are of different sizes and lengths, so it is important to label the screws correctly. Keep your motor away from your screws as well; it will attract them and confuse you and your labeling system will have been for nothing.

Motor Cage Unit Removal

Turn the gearbox on its opposite side so that the wires face you. The wires should be tucked under a gearbox “arm” at the top. BEFORE removing the arm, you must ease the wires out from under the arm. Failure to do so can result in a mess of frayed wires. Using a flathead screwdriver as a lever, apply enough pressure to ease the arm’s wire retainers upwards from the gearbox. Gently pull the wires out from under the retainers. You’ll have to do this three times for all three retainers. After the wire has been separated and is free, you can use the screwdriver and mallet to force the arm down the gearbox. Place the flathead against the rear of the arm and use the mallet to push it down the top of the gearbox. When a small section of the arm protrudes from the front of the gearbox, you can grip it and pull it off with moderate force. Do not bend or flex the metal arm, as this can cause damage to the part.

External Wire Placement
Gearbox Rail Removal

There are a total of 4 screws that need to be removed to separate the gearbox halves. All four can be removed with the same Allen wrench as the smaller of the two types for the bottom grip screws. The gearbox needs to be placed on its left side in order for the screws to be removed. Two screws are located at the end of the gearbox towards the motor wiring. One screw is located at the top of the gearbox at the front, just above the nozzle. This screw is much smaller than the others. The last screw is the second from the left on a metal plate on the lower right section of the right side of the gearbox. This screw is slightly longer than the other two screws from the back of the gearbox. Do not confuse this screw with the others. All screws should be labeled and recorded.
Next, remove the plastic gear cover on the gearbox shells behind the trigger. It can flex easily, so ease it out of its place. However, it can flex only to a point. The plastic can break if it is flexed too much, or if it is not removed before the separation of te gearboxes.

Gearbox Screws Removal

Now the gearbox shell halves are ready to be separated. Keep the gearbox on its let side. Be slow and careful. Use minimal force at first to gently pull the shells apart. If they are not budging, gradually add more force. If they do not budge at all, check to see if every external screw was removed. Check to see of the small screw at the front of the gearbox above the black nozzle was removed.
No harm done if your spring flew out. I did not experience a spring explosion, but I was extremely careful. There is no need to fuss with a screwdriver holding the spring in place like in the Version 2 gearboxes. Go ahead and separate the gearbox shells. There might be a pop as tension on the parts is released. The trigger unit may have fallen out as well. There are three pieces within the trigger set: the trigger, a trigger catch, and a spring. Label and place these on a card.

Seperating Gearbox Shells

Depending on if the gearbox was used heavily or moderately, varying conditions of the gearbox will be present. You might see globs of thick black grease and discolored metal and simply what one may describe as a “mess.” Photographs become very helpful at this point, as the various parts can confuse a new airsofter. Before making another step, take note of the shims, the thin spacers of metal that may be stuck on the nylon bushings on the other half of the gearbox. These are supposed to be between the gears and the bushings. Record the number of shims present and place them on their notecard. If you are not planning to do a reshim job, then it is especially important that you record the factory-setting shims. Later, you will be doing the same recording for the other side. Take note that the shims are of different sizes, so they must be organized by size and number. I usually draw a crude sketch of the gears and axles then place the shims on the paper next to their appropriate places designated by my drawings.

Gear Shims

Firstly, if the trigger unit has not already been placed and labeled, go ahead and do so. Next, apply pressure to the spring guide, located at the top of the gearbox in the cylinder-compression area. Push the spring guide so that it can be eased out of the piston and the gearbox. Place the parts on their respective labeled notecards or Post-its. Wipe down the parts with the cloth to remove old grease and debris.

Compression Unit Removal

Next, remove the tappet plate and the cylinder compression unit. The unit includes the cylinder head, the cylinder, air nozzle, and the piston/piston head. As you remove the cylinder compression unit, take care to remove the tappet plate. It is the long, black piece of plastic that is connected to the air nozzle. It is also attached by a spring to a single rod from the gearbox shell. Release the spring from the rod. After that, the entire compression unit should be free to pull up and out of the gearbox. The small black plastic piece within the wiring box should be removed as well. Wipe down all components. Rinse them with water if you would like, but dry them thoroughly, as the metal components can oxidize. A brush greatly aids in the removal of grease and debris from between the teeth of the piston.
Now, pull up on the sector gear. It is the thickest and has a series of holes on the face of the gear. It should pop out relatively easily. Be sure not to lose the shims that are present on the other side of the gear. Record these settings if you have not done so already. Wipe down this gear as best as possible and remove any old grease and debris with the cloth, then place it on its respective notecard. The process should be repeated for the bevel and spur gear. Running water can remove debris as well, but be sure to dry the gears thoroughly or they can oxidize. The use of a brush greatly aids in removing grease and debris from between the teeth of the gears.

Gear Removal

Once the gears are removed, pull out the anti-reversal latch. It is located at the left of where the bevel gear used to be. Do not lose the spring that comes with it. Clean the latch, then record and place on a card.
At this point, the gearbox should look pretty cleaned out, aside from the old grease and the selector switch assembly. The selector switch wires should be connected to an odd roughly-shaped box. Leave it alone for later; it is okay if it is free and floating.
On either side of the gearbox shells are two metal latches built into the shell. One of the latches is located on the inside of the left side shell that can be removed with a small-sized Phillips screwdriver. Save the spring and the latch, remember how they were placed or take another picture, then clean and label them. The right side latch functions for the safety. To remove it, you need to use a small Allen wrench of the same size as the smaller of the grip screws and the gearbox shell screws. There should only be one crew left for the plate. Once the plate is separated from the side of the right shell, note the pieces, which include a small spring.

Right Side Latch Removal
Left Side Latch Removal

Turn the left shell of the gearbox over on its right side. The selector switch should be on the outer surface of the shell. It will take some time, but to remove the selector switch, you need to wriggle it out of its slot. Some bending and flexing will be necessary, but do not overdo it and snap the switch. Ease it out from its slot through the side, right or left. The key is to encourage the switch out of its retainers of the gearbox one at a time from the right side. Once removed, briefly wipe the copper plate with a damp cloth. Debris and grease can disturb the current. Wipe, clean, then dry thoroughly. Oxidation of the selector switch is especially troublesome. Your ability to switch between semi and full-automatic, or the ability to shoot at all, will be deterred.

Selector Switch Removal

Flip the gearbox shell back onto its left side. Pull the selector switch assembly slightly outwards so you have some slack in the wire to work on dissembling it.
The switch assembly should have two wires extending from it. There are also two screws located on the switch box. One is visible at the moment, but the other is revealed upon the removal of the first screw. Both need to be removed with the small Phillip’s head screwdriver used to remove the long latch from the left side of the gearbox. One a screw is removed, a black plastic fitter fill become loose. The position of the black piece is not impossible to reassemble later, but a detailed photograph helps. Ease the two wires out as its corresponding screw and plastic fitter is removed. Each wire has a copper metal sheet bent into specific shapes. It is important that these copper sheets retain their shape. Once the switch assembly is disassembled, the wires can be pulled through the hole in the gearbox. Now the motor and its wires can be completely free from the gearbox. Set aside from the metal tools and parts in a safe place where the copper ends can be protected. Do not fool around with the wires, especially near the area close to the motor. The wires have been soldered onto specific points that give the internal magnetic coil its current. A re-solder job will be necessary if there is damage to the connection. A helpful hint is to wipe down the copper ends, like the selector switch, to remove any debris that can affect the electric flow.

Electrical Box Disassembly

Using a thick Allen wrench or metal rod roughly 6-8 millimeters in diameter (possibly even one of your BBs), rap out the nylon bushings. The bushings should either be the original yellow-cream colored or black from all the grease. A sharp tap with the rubber mallet should knock them out. They can be damaged if excessive force is used, but chances are that they need to be replaced anyways. Nylon is not as durable as steel, and I highly recommend steel bushings, which come in oil-less or oil chambered designs.

Bushing Removal

If desired, the piston head can be removed from the piston. A Phillips head screwdriver can be used to remove a screw located inside the piston. This screw allows for a firm connection between the face of the piston and the piston head. Once the screw is removed, the piston head can be removed from the front of the piston. The screw and a round retainer should be able to be removed from inside the piston.
Congratulations! The entire internals of the gearbox has been stripped down to the last screw. The gearbox shells should be completely empty. Now you can wipe it down, clean and wash out the old grease. Wipe down every corner of the gearbox. Old, leftover grease attracts unnecessary dust and should be removed. Watch out for the small corners where a ball of old grease can reside. You can also inspect the gearbox for any signs of damage, such as cracks, splits, or broken pieces. The best way to remove any trace of grease is to use dishwasher cleaner. The amphiphilic organic compounds and surfactants lower surface tension, which allows for grease and other gel and liquid substances to break apart and dissolve. Be sure to dry thoroughly so the metal does not oxidize.
Finally, give all your individual components that you removed a final look-over for grease or debris that was left behind and wipe them off. You will notice why it is important to keep a work area relatively organized, as you will have covered half the table with pieces and parts, each which has its own specified place in the gearbox. Make sure there are no random pieces “floating around” on your work surface. If a part is found that you do not know where it belongs, save it until it can be identified from your visual guides.
This guide has broken down every step in field-stripping the UMG and dissembling the gearbox. If any part has been damaged upon inspection or shows significant signs of wear, it is best to replace the part immediately. Waiting until after the part is broken is not a smart choice and will lead to more serious problems with your UMG such as chain reactions or multiple parts failure.

When reassembling the UMG and its gearbox, the steps described above are basically reversed. However, several points and additional steps apply, especially to the gearbox components.
Hopefully, you have purchased steel bushings (oil or oil-less) and steel shims. Both are highly recommended, even with the stock components and spring. Begin the reassembly by applying the bushings in the gearbox holes. Steel bushings tend to be larger than the stock gearbox holes. You will most likely have trouble forcing the bushings into the UMG gearbox holes. The solution to the problem is simple: use the properties of temperature. Heat is the transfer of energy from one substance’s molecules to another’s. Therefore, adding heat to the gearbox holes should “excite” the molecules, creating more movement molecularly and expanding the holes. At the same time, cooler temperatures inhibit the flow of heat, therefore slowing the vibration of molecules and contracting the material. Freezing the bushings will make them smaller, and applying heat with a hair dryer to the gearbox holes will expand them. The process does not use filing, which can permanently damage the gearbox shells if done improperly.
Once the correct temperatures has been reached (to the point where each component feels hot or cold to the touch), quickly hammer the bushings in so that the metal does not lose their temperature settings. This is when a rubber mallet is safer to use than a steel hammer. A steel hammer can cause some damage to the gearbox. Go ahead and use force to get the bushings in. Remember, this process is helpful for tight-fitting bushings and does not have to be applied to normal-fitting bushings. Loose-fitting bushings are problematic and would require more drastic measures such as bushing enlargement or even gearbox replacement. This is why I would avoid using files and hole-enlargement.


A reshim job will be necessary when purchasing steel bushings and steel shims. A reshim job’s purpose is to reduce the space between the gears’ axles and the bushings. Shims come in different thickness and sizes, which varies depending on the manufacturer.
Place the left gearbox shell on the work surface with the inside facing up towards you. Slide the thinnest shim onto the bottom axle of the spur gear, then place the spur gear in its proper hole. Check the space between the bottom face of the spur gear and the gearbox. There should be just enough clearance for the gear to spin without touching the gearbox. Spin the gear while applying force directly down the axle. Do not tip the axle in any other direction. If the gear face touches the gearbox, replace the shim with another shim of the next thickness, then retest. If it appears that it spins without touching the gearbox, then screw together both gearbox shell halves (remember to retain the screw numbers so they are not confused with each other later).


Place the gearbox on its left side. Using a small screwdriver with a flat head, place it under the spur gear face that is against the gearbox side. Lift up the screwdriver. If it slides upwards, you will need to apply shims on the axle. As you lift up the spur gear, watch the axle rise in its bushing. The distance it rises is roughly the thickness of the shims you need to apply.

Bushing to Axle Measurement

Take apart the gearbox again and place the screws on their appropriate cards. Take a medium thickness shim and add it to the opposite axle that you originally placed the first shim.
Again, close up the gearbox and using the screwdriver, check for any space. Additionally, spin the gear. You want to continue adding shims to the axle that will engage into the right side of the gearbox, not on the side that is against the gearbox side. Add shims until there is no space or very little, but the gear spins freely.
Repeat the process described above for both the remaining gears: the bevel and sector gear. Remember, add shims to the right side of the gears until they spin freely but do not slide side to side in their bushings. You will have to close the gearbox repeatedly and spin the gears by reaching into the gearbox with a screwdriver to test the shimming.
The process is time consuming. Be patient and do not rush. Adding too many shims will lock up your gears while adding too few will strip your gear teeth. Take time to do the job properly.


Lubricants greatly decrease the amount of friction between components. The smooth engagement of individual parts in the gearbox is crucial in a top-performing airsoft replica. Less friction reduces wear on components inside the gearbox, such as the gears and piston.
The recommended lubricants are greases. Greases are in the gel form and provide long-lasting performance. Spray lubricants do not last as long as greases and are not as well suited for moving metal parts. Liquid lubricants run in every direction and do not lubricate the intended part for long.
The most suitable grease is white lithium grease. White lithium grease is very cheap, resists water and moisture, and performs well even under higher temperatures. It is recommended to purchase a tube of white lithium grease rather than a canister. A tube can apply the grease in a finer pattern, which is useful for the small components of the gearbox.

White Lithium Grease Tube

The white lithium grease should be applied to the components where constant rubbing and friction occurs. This includes the bushings, the gear axles, the gears’ teeth and faces, the piston rails, the gearbox rails, the tappet plate rails, and possibly the cylinder head nozzle. Use enough grease to reduce the friction at points of contact, but not so much that dust is attracted to the grease and a results in a mess.

Gearbox View for Greasing

After your reshim job, you are ready to grease your gears. Remember your formation of the shims and set them aside, then apply grease to both faces of the gear. Spread the grease evenly across the surface. Apply grease to the teeth as evenly as possible and try to work them between the teeth. Grease the axles as well.


In contrast to many guides written, it is my personal belief that the reassembly of a mechanical apparatus is NOT as simple as “reverse the order of the steps made in disassembly.” Several intermediate steps that were not made in disassembly need to be addressed in reassembly to avoid future problems.
The first step is to reinstall the two latches for the safety and semi-automatic mode fire. When installing the left side latch, take care not to strip the screw with the Phillips head screwdriver. It is an incredibly small head, and it is easy to over-tighten it, which can ruin your screw head. When installing the right side plate that controls the safety, only install the left screw of the plate.
If you have not done so already, place your left gearbox shell on your work space, and then place your configured shim arrangement back onto your gear axles. Take the spur gear and place it in the correct bushing while keeping the shims arrangement intact. Next, take the anti-reversal latch. Place the included spring on the latch so that the hook wraps around the arm of the latch. Place the anti-reversal latch in its proper hole on the gearbox. When properly placed, the latch should have one wire of the spring placed against the gearbox shell and the hook providing tension on the arm. Take the bevel gear, with its shims, and place it in its proper bushing. The anti-reversal latch will need to be pushed back against the tension of its spring to fit the bevel gear. Make sure that the arm of the anti-reversal latch is engaging the swirl-like pattern of the bevel gear. This is what prevents the gears from unwinding after a compression cycle. Finally, take the sector gear, with its shims, and place it in its proper bushing. Rotate the gear to engage the spur gear’s teeth correctly.
The core of the electrical workings of the UMG lies in the switch assembly. No doubt the switch assembly and wiring can pose some difficulty during reassembly.
Firstly, the wires with the copper ends need to be reattached to the black box via the screws and plastic fittings. Insert the copper ending that tapers to a rounded end into the black box so the copper ending is symmetrical to its partner copper end. Attach the appropriate fitting onto the wire. A small protruding end on the fitting should be engaged into the switch assembly box. This piece acts as a separator between the two copper ends.

Electrical Box Reassembly

Next, place the other copper end onto the side of the box, then clamp down with the appropriate plastic fitting and its screw. The fitting has a small L-shaped end that loops across the back of the box where the first copper wire fitting was attached.
After wiring has been reestablished, take the second part of the switch assembly, the current connector, and place inside the box. The small circle nubs should fit effortlessly into grooves inside the box. The circles should be lower than the rest of the current connector.
Next, position the box into the gearbox. The box should be placed accordingly to its surrounding fit in the front, lower section of the gearbox. A good guide is the small protruding side of the black box, which fits nicely into a small cutout of the gearbox above it.
If the piston head was separated from the piston, reassemble it. Drop the screw through its retainer, then drop them together down the piston. It will take several attempts and readjustment to properly drop the retainer and screw down the piston. When done correctly, the end of the screw should be exposed through the hole. Place the piston head over the end, then use the screwdriver to tighten the screw.
Before assembling the compression unit, test the actual compression yourself. Fit the cylinder head into the cylinder, and then place a finger over the cylinder head’s nozzle. Taking the piston and piston head unit, push it down the cylinder while keeping your finger over the nozzle. If done correctly, the piston should be extremely hard to push down the barrel once the piston head is pushed past the hole in the cylinder. If not, examine the o-ring on the piston head. It may be “clogged” with grease and is not expanding correctly; ease it out of its groove and wipe it clean. If that does not solve the problem, it may be worn or simply too old, in which case a new o-ring or piston head should be purchased.
Next, insert the cylinder head into the cylinder. It is recommended that you fit the cylinder head in the gearbox so that its holes are facing side to side and the cylinder’s relief hole is facing either right or left. This cylinder relief hole should be visible when the gearbox shells are screwed together. It is best to position the cylinder so that the hole is towards the back of the gearbox. The piston should fit in nicely, with its teeth facing downwards and the grooves able to slide on the gearbox rails.

Air Compression Sealant Test

Once the cylinder head is positioned correctly in the cylinder, slide the air nozzle over the cylinder head nozzle.
The tappet plate head should fit into the air nozzle’s crevice running around the base of the air nozzle. Position the tappet plate so that the entire plate head section can slide down the nozzle into the cutout of the rim of the cylinder head. The tappet plate spring can then be looped around the small hook located under the tappet plate. The spring has two loops, each which protrudes at a different angle. Position the loop on the spring so that when it is placed onto the hook of the tappet plate, the spring coil itself has enough room to decompress and compress.
At this point, the compression unit, the gears, bushings, shims, switch assembly, anti-reversal latch, and the gearbox latches should be reinstalled.
The taper spring and spring guide are the driving force behind the power of an airsoft gun. Using an overpowered spring in an under-upgraded gearbox WILL destroy several components, including possible damage to the gearbox shell itself. However, if you wish to increase your FPS, or want to correct a loss of FPS, you can re-stretch the old spring.
Slide one end of the spring over the spring guide; it does not matter which end. Slide the open end of the spring into the piston, which should already be in place in the gearbox. Using force, position the spring guide while keeping tension on the spring so that one metal bar fits into its cutout at the end of the gearbox. If done correctly, the spring, compression unit, and the other components should be able to hold their own without the other gearbox half.
The trigger assembly is a frustrating part to deal with. Place the spring on the gearbox. The hole the spring should be placed in is the first from the electrical box. A small, barely noticeable hole or opening in the gearbox is where the short protruding part of the trigger spring goes; do not confuse the short end with the longer end at the other end of the spring. Hook the metal sear over the back rod of the trigger correctly so that the sear catch’s flat side is facing away from the trigger. Now, place the trigger unit in the last open space in the gearbox near the switch assembly on top of the spring. Line up the holes with the trigger rod and sear rod. The spring will give will give stout resistance and many attempts will have to be made to get the trigger correctly installed. It is good enough to line up the holes, as when the second half of the gearbox shell is installed, the trigger becomes easier to place. By itself without the other half of the gearbox shell, the trigger cannot stay in its holes, so when you are putting the shells back together, ease the trigger, against its spring, into its holes in both gearbox shells. Practice makes the process significantly easier over time.

Trigger Reassembly

Take this opportunity to become familiar with the operations of the gearbox. All components should be installed. If you rotate the bevel gear, you will see that all the gears will turn. As they turn, the sector gear pulls back the piston back against the tension of the spring. At the same time, the tappet plate will be pulled back against its own spring tension with the small metal nub on the sector gear (you might need to hold down the tappet plate onto the nub to see it work). The tension of the spring may be too tough to continue, but if the gears were to keep turning, then eventually the sector gear’s teeth would end, the piston would be released, and the force of the spring would push the piston and piston head down the cylinder to shove whatever air is there through the cylinder head and to the BB.
Now is the time to close the gearbox. Take the right shell and place it loosely over the left shell. As you do, try to position the trigger so that its rods line up in the holes. Some force will be necessary to get it in the hole, as the trigger spring offers resistance. At the same time, the anti-reversal latch tends to shift out of positions lightly, which blocks the gearbox shell from being placed securely. Poke at it with a small screwdriver through the gap between the gearbox shells to persuade it into its hole.
This step involves much patience. Oftentimes you will need to restart the step and take off the shell, then reinstall. Shims can become detached from their axles, springs released, and the trigger can become loose. Constantly “fiddle” around, and eventually, the shells will align. When they do, immediately apply screws to their appropriate holes while keeping pressure on the gearbox side so it does not unexpectedly pop. Next, screw the motor cage unit onto the bottom of the gearbox, with the open part of the cage facing outwards.

Latch Preventing Gearbox Closing

At this point, the gearbox has been examined, reinstalled, greased, maybe even upgraded, and fully assembled. Test the internals by connecting the battery to its connector and pulling the trigger. Make sure the selector plate is making contact with the copper fittings in the gearbox. If everything has been installed correctly, the internals should cycle normally. A compression lock-up can be caused by a new and stiff piston head o-ring. Simple disassemble and remove, apply a little liquid grease and reinstall. Using petroleum based lubricants will damage the rubber o-ring, so use normal lubricants. A gear lock-up is usually caused by too many shims on the axles. Redo your shim job with more precision and testing. If any problem arises and the internals do not fully cycle, do not continue holding down the trigger. The motor will be put under incredible stress, the wires will heat up tremendously from the increased current resistance, and electrically, the gun may fail. Usually, two to five reassemblies solve the problem. Diagnose the problem, fix it, and then reinstall. (Should you have problems, you can ask me to fix it. Send me an e-mail or personal message, and I will contact you about the situation).
Next, replace the stopper rail onto the top of the gearbox. Use a rubber mallet or some kind of hammer to slide it back onto the top rail of the gearbox. Whatever you do to replace the rail, take care to not bend the rail. Replacement rails can be found, but it best to eliminate unnecessary repair costs. The wire “hooks” should be on the left side of the gearbox, with the longer retainer facing towards the front of the gearbox. Once the rail is properly placed back onto the gearbox rail, ease the wires from the gearbox under it. Try to place the rubber-wrapped part of the wires under the rail; the rubber prevents the silicone insulation of the wires from fraying. You can use a flat-head screwdriver as a lever to ease the retainers upwards so the wires can slide underneath.
Position the wires correctly as they were before the disassembly process. Photos taken during the process are a big help here, as repositioning the wires so they do not twist, bend, or rub unnecessarily are crucial or a long-lasting gearbox. Obviously, it will not work with frayed wiring! Note that the wiring should begin from the bottom of the motor then travel upwards. The positive (red) wire will be set into a groove towards the top of the motor cage unit, while the black wire will wrap around the cage.

Wiring Placement

At this point, the gearbox should be restored to its original state, or in an even better state. Run a final test by connecting the battery to the Tamaiya connector and make sure the internals cycle completely.

Stock Internal Component Examination

G&G crafted an excellent model of the UMP externally. However, an airsoft gun with indecent internal components can only serve as a good-looking paperweight. This next section provides a brief overview of the individual parts of the UMG and their performance. My personal UMG has been used heavily, so descriptions of wear over time are based on experience.
Arguably, the most important part of an airsoft gun’s internals can be the gearbox shells itself. They hold together all components and provide support. The UMG gearbox is a version 3, comprised of zinc alloys (to the best of my knowledge). Cast by molds, the gearbox shells are one-piece and offer high-density strength and great support. Over time, I have not seen any cracks, excessive wear, or unintentional widening of holes and grooves.
The drive spring provides the power for the compression unit. The stock spring has remarkably retained good FPS over a long period of time with no signs of cracking or bent coils. A good spring stretch does not hurt once in a while.
The spring guide is surprisingly of good quality. It even offers a revolving plastic base that imitates bearing spring guides. Normal spring guides do not accommodate the twisting of springs as they compress, which decreased their life. The entire construction, save for the retention base, is made of either polycarbonate or ABS plastic, strong enough for even an upgraded spring. However, I would still recommend using a bearing guide to further reduce spring coil twisting.
The piston is of polycarbonate (to the best of my knowledge) and is extremely tough. I believe it to be higher quality than the Systema polycarbonate pistons. The first tooth that engages the sector gear is made of steel to prevent chipping. The other teeth show no signs of wear at all. The hole where the piston head connects to has no signs of cracking.
The stock cylinder is made of polished brass, which has self-lubricating properties. It offers low friction but high strength. There is wear on the inside of my cylinder, but it does not seem to affect performance. An auto polisher can remove minor scratches on the brass.
The piston head is one part I was not impressed with. Although the material itself is superb, the o-ring and its groove are under par with compression. After medium use, the o-ring was unable to expand properly during compression and the groove was too large, leaking 80% of the air generated. I would recommend buying a new piston head to improve long-term compression and to increase FPS.
The cylinder head was of decent quality. The design utilizes a milled brass nozzle set into a plastic base with a single o-ring around it to provide a seal against the cylinder. The design is weak, as the nozzle become loose in the plastic. The plastic does not feel as durable as I would have preferred either. I replaced it with a solid milled brass head one-piece, which offers 60% better stability, 100% better strength, and 10% better compression.
The air nozzle is a simple design, the same compared to other brands. There is minor wear on my nozzle, but no cracks or damage that would render it inoperable. It is made of a medium-grade plastic.
The sector, bevel, spur, and pinion gear are made of steel (to the best of my knowledge). They are quite dense and durable, but after heavy use, the teeth show signs of chipping and wear. My current G&G gears have medium damage to the bevel and pinion gear and minor damage to the spur gear, with none to the sector gear. I would recommend upgrading to either high-speed, high-torque, or Guarder gears. However, if the gun is meant to operate stock, then chipped gears should not be a problem for a long time.
The bushings are of inferior quality. They are made of nylon, which can deteriorate under heat and use. My spur gear bushing actually collapsed; the extended part of the bushing was shoved into the flat part that lies on the gearbox shell, rendering the bushings completely useless. I have installed solid steel bushings, which have showed an increase in durability and have decreased friction. I highly recommend purchasing new bushings, especially when upgrading.
The shims were of good quality. I had no problem with them, but found that more sizes were necessary when upgrading. They are made of steel and are strong; you should not encounter shredded shims.
There has been criticism on the G&G tappet plate, which has weaknesses in feeding. I did experience minor mis-feeds, but the problem completely disappeared when I upgraded. I cannot say exactly how my mis-feeds disappeared. The stock tappet plate is more flexible than I want, but it shows no signs of tear or cracks. I am still using my stock plate with no problems. I have received word however, that G&G’s new version of their UMG tappet plate is material-wise weaker than the original. I would recommend finding a polycarbonate plate by Systema or Guarder.

The Guay & Guay UMG is truly a model to be recognized. G&G has simplified the take-down process for easy maintenance. The internals maintain a low-cost, both for the manufacturer and the user, but offers good quality and durability, save for the bushings and piston head. In addition, and perhaps most importantly, you now can disassemble you UMG and most version 3 gearboxes. For whatever purpose you disassemble your UMG and/or a version 3 gearbox, you can take it step-by-step and make a great airsoft replica even better.

Edited by New Guy on the Block, 25 January 2007 - 01:20 PM.

  • 0

#2 kiki-jiki

  • Gender:Male
  • Location:Ann Arbor, MI
  • Interests:Airsoft, guitar, cars, school (University of Michigan)

Posted 25 January 2007 - 01:00 PM

Holy crap..and you didn't think it was that good. That was long, and VERY in depth. I vote for a sticky....
  • 0

#3 hsimoorb

  • Location:Springfield, Ill
  • Interests:Baseball, History,

Posted 25 January 2007 - 01:34 PM

Wow, that is an impressive write up. Sticky for sure. Also, I'm glad to hear some good things about the gun internaly. I have heard very bad things about them, particularly from Arnies' users, though I never got some hard evidence for their supposed internal weakness. I think you've cleared all that up now.
  • 0

#4 assaultmonkey

  • Location:United States, MI
  • Interests:Other than airsoft?<br />I like to skateboard, snowboard, playing my guitar,<br />BMX, Paintball, and pretty much music in general.

Posted 25 January 2007 - 02:29 PM

That was very.......in depth.
Good job, that must have taken forever to write.
Like everybody else said, This must be stickied.....This why ASF is so great....because for every newbie out there asking a which gun question, you get somebody really dedicated to the sport that helps people out and shares information like this.
  • 0
If you understand the difference between a sniper rifle and a sniper, but aren't an annoying
enough of a person to correct people, put this in your sig
There's no sweetness in success without a chance of failure
QUOTE (assaultmonkey' @ Mar 8 2007, 11:25 AM)
Haha I quoted myself

#5 OWN3D!


Posted 25 January 2007 - 08:45 PM

I vote Yea on the sticky ballot.
  • 0
Banned Member

#6 Tweekage

  • Location:CORONA, CA
  • Interests:Airsoft, Paintball, Xbox, Computers, etc.

Posted 25 January 2007 - 11:05 PM


How long did this take?

Wow. Awesome guide.
  • 0

#7 Mc Master

Mc Master
  • Gender:Male
  • Location:Southern California

Posted 28 January 2007 - 05:06 AM

thank you, needed this as I am getting this gun in 4 days. And I ahve to upgrade myself.
  • 0
A signature.

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0


  • Gender:Male
  • Location:Lakewood, Colorado
  • Interests:Skiing, Airsoft, XBOX, Building replica LEGO guns, and, The DENVER BRONCOS!

Posted 29 January 2007 - 03:55 AM

Why hasn't this been stickied yet?
  • 0
I need so much more experience, so please, take what I say, compare it with what experts say, and what I've personally done, and your experience as well...I'd rather you get the right answer in the end than just take me at my word if I'm wrong or even if I'm right.

:-) Good day.



    The New Guy on the Block isn't so new anymore...

  • Forum Administrator
  • 6,855 posts
  • Gender:Male
  • Location:Fairfax Station, Northern Virginia
  • Interests:I love to drive and work on SAAB cars<br /><br />Alumni of the Thomas Jefferson High School for Science and Technology **RANKED BEST HIGH SCHOOL IN THE US BY USNEWS**<br /><br />Undergraduate Industrial Systems Engineering at the Virginia Polytechnic Institute

Posted 01 February 2007 - 08:00 PM

I'll ask a mod now to sticky; I'd rather be humble and wait for a pin, but I can ask a mod. Wish me luck!
  • 0

#10 Guest_triggerhappy_*


Posted 01 February 2007 - 08:38 PM

Wow, nice guide. Pinned.
  • 0

#11 NGOB


    The New Guy on the Block isn't so new anymore...

  • Forum Administrator
  • 6,855 posts
  • Gender:Male
  • Location:Fairfax Station, Northern Virginia
  • Interests:I love to drive and work on SAAB cars<br /><br />Alumni of the Thomas Jefferson High School for Science and Technology **RANKED BEST HIGH SCHOOL IN THE US BY USNEWS**<br /><br />Undergraduate Industrial Systems Engineering at the Virginia Polytechnic Institute

Posted 23 February 2007 - 04:32 PM

I would like to put this forth now as a helpful hint to any new player or first-timer with their gearbox:

Airsoft retailers sell their greases and lubes anywhere from 100% to 600% of the cost of another tube of better grease with 5 times the volume. Consider a $15 tiny tube of gear grease, compared to a gigantic $3 automobile lithium-grease. See my point? You can save money from buying a brand name grease by buying the same stuff at a fraction of the cost and get more your your buck.
  • 0

#12 Nailz

  • Gender:Male
  • Location:Marina, California
  • Interests:Airsoft, First Person Shooters, Single Malt Scotch, Music Health Care and my lovely wife, son and daughter.<br /><br />xfire- nailz69

Posted 16 March 2007 - 02:22 AM

Paint me impressed. a-thumbsup.gif
  • 0

I Am The Push That Makes You Move

#13 Icey101

  • Gender:Male
  • Location:Albuquerque, NM

Posted 16 March 2007 - 03:06 AM

Alot of the UMGs have issues stock. Of the 4 I have dealt with first hand. Two had issues with compression stock, one worked like champ just wouldn't feed right (broken cylinder head nozzle), and the fourth came pre upgraded from WGC. From the examples I have seen I do not recommend the gun to someone unless they want to work on it or have someone else work on it. That all being said.....it is my favorite AEG I have ever owned (and I have owned alot).
  • 0

#14 NGOB


    The New Guy on the Block isn't so new anymore...

  • Forum Administrator
  • 6,855 posts
  • Gender:Male
  • Location:Fairfax Station, Northern Virginia
  • Interests:I love to drive and work on SAAB cars<br /><br />Alumni of the Thomas Jefferson High School for Science and Technology **RANKED BEST HIGH SCHOOL IN THE US BY USNEWS**<br /><br />Undergraduate Industrial Systems Engineering at the Virginia Polytechnic Institute

Posted 16 March 2007 - 09:13 PM

Interesting...the only problem I've EVER seen was people breaking off their cocking handle...

Though I can see problems with compression and the cylinder head nozzle...but that's when people abuse their guns. A cylinder-head nozzle breaking, especially of this design, will break if the hop-up is not pushed in when the lower receiver is taken off. So that isn't a problem; it's a user issue.
  • 0

#15 NGOB


    The New Guy on the Block isn't so new anymore...

  • Forum Administrator
  • 6,855 posts
  • Gender:Male
  • Location:Fairfax Station, Northern Virginia
  • Interests:I love to drive and work on SAAB cars<br /><br />Alumni of the Thomas Jefferson High School for Science and Technology **RANKED BEST HIGH SCHOOL IN THE US BY USNEWS**<br /><br />Undergraduate Industrial Systems Engineering at the Virginia Polytechnic Institute

Posted 24 April 2007 - 05:26 PM

I found replacing the gears with Guarder ones is an excellent choice if you want to replace gears. They fit fine in the GB and function perfectly. I believe them to be more resiliant to stress as well compared to the old one, and can pull stronger springs.

So, should you need low-cost and effective gears, try the Guarder ones, because they work fine in the UMG GB.
  • 0

#16 ah dinosaur!

ah dinosaur!

    Invest, Repair, Sell, Repeat

  • Authorized Seller Free
  • 1,219 posts
  • Gender:Male
  • Location:North California
  • Interests:I've just gotten into actual airsoft gaming, and I'm quite enjoying it. I do still enjoy 'chairsofting' and the part of airsoft away from the field. I sell A LOT of stuff, check out my sales.
  • SOA Name: ah dinosaur

Posted 25 May 2008 - 09:18 PM

you didn't say anything about timing the gears. I've hear mixed things on whether or not this is necessary. what's your take?
  • 0
Check my Sales!
QUOTE (NUSCerick @ Dec 31 2009, 09:40 AM) <{POST_SNAPBACK}>
do you snipe, or actually play airsoft...

#17 NGOB


    The New Guy on the Block isn't so new anymore...

  • Forum Administrator
  • 6,855 posts
  • Gender:Male
  • Location:Fairfax Station, Northern Virginia
  • Interests:I love to drive and work on SAAB cars<br /><br />Alumni of the Thomas Jefferson High School for Science and Technology **RANKED BEST HIGH SCHOOL IN THE US BY USNEWS**<br /><br />Undergraduate Industrial Systems Engineering at the Virginia Polytechnic Institute

Posted 28 May 2008 - 05:48 AM

There's no such thing as timing...the entire gearbox resets itself with a cycle.
  • 0

#18 crusader4x

  • Location:Shoreline, WA
  • Interests:Airsoft<br />RC Touring Cars, Monster Trucks, Helicopters, and Airplanes<br />Warmachine<br />Boardgames

Posted 12 September 2008 - 06:37 PM

A bit of a necropost BUT, I'm literally rebuilding an aftermarket gearbox from spare parts to put into the UMG body I have. Can anybody tell me if a ported cylinder would be better? Also, does anyone know where I can get an extra set of THESE PARTS for my gearbox. Finding, finding UMG specific nozzles has been a pain, is it a standard G36c nozzle?

Edited by crusader4x, 12 September 2008 - 06:40 PM.

  • 0

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users