Echo 1 / A&K M249 SAW Para Gearbox Disassembly/Assembly

This guide shows the steps required to remove the gearbox from the Echo 1 or A&K M249, as well as how to disassemble and re-assemble the gearbox. the M249 SAW gearbox is one of the easiest gearboxes to work on, partly because you can remove the main spring before opening the gearbox. Also, there are quite a few less parts, as it is set up to fire full auto only and this makes maintenance much simpler. The gearbox, as it comes from the factory should be re-greased before use, as they do not do a very good job.

Re-shimming the gearbox is also recommended, although you can get by with the factory settings. You can use any Version 2 gearbox shim guide on the web to perform this task and there are a few good ones available. Tips for upgrading parts are also listed along the way and the gearbox is compatible with standard Version 2 Gearbox components. Any questions should be directed to

1 Remove the barrel by pressing the release lever on the left side, then pull the barrel forward until the upper hand guard hits the front of the receiver, lift it up and over the receiver and remove the outer barrel assembly
2 Remove the inner barrel assembly by pulling it forward and out
3 There is a notch on the Hopup that engages with a slot on the gearbox. Be sure to re-install correctly and note that the right side that is smaller in diameter actually inserts flush into the gearbox
4 Disconnect the fuse wiring harness from the two gearbox wires
5 Remove the Rear Stock retaining bolt by turning the thumb screw on the right side. If the bolt is difficult to remove, re-install the thumb screw a couple of turns and use it to push the bolt out through the left side
6 Once loose, remove the Rear Stock retaining bolt
7 On the Para version, position the Rear Stock as shown, then fold the stock down and use it as a stand as shown in the next photo
8 Pull the front of the spring latch on top of the gearbox rearward while pushing in the Spring guide assembly. once it unlatches, remove the spring guide
9 Hold the latch back, as it can catch the spring if not held, then remove the main spring
10 Squeeze the two release knobs inward and lift up the Loading Hatch
11 Remove the two Gearbox retaining screws from the left side of the receiver using a 2.5mm wrench
12 Pull the charging handle forward a couple of inches until it clears the spring rod. You may have to remove the hatch screw on the right side to move it forward
13 Push the gearbox rearward and pull the two wires through the hatch cover hole, then remove the gearbox as shown
14 The M249 Gearbox is shown
15 Cut the tie wrap holding the wires to the gearbox and disreguard
16 Remove the red power wire from the motor. The motor has a red spot on top of the spring guide identifying the positive terminal
17 Remove the black wire from the motor terminal on the other side
18 Set the black wire aside
19 You do not have to remove the two screws identified in the photo, as they are used to mount the trigger switch
20 Use a 2.5mm wrench and remove the gearbox screws
21 Remove all the screws identified in the photo
22 Remove the upper half of the gearbox
23 Feed the red wire back through the hole
24 Set the upper half of the gearbox aside with the inside facing up. Be careful to not disturb any shims still stuck to the bearings. The glob of grease shown is all that was in the gearbox and it barely touched any gears, as if they just shot a glob in with a grease gun
25 This photo is for reference and shows the location of all the gearbox components
26 If you wish to keep the shims in place, remove any shims from the top of the Sector gear and place on the right top side of a clean paper towel
27 Remove shims from the other gears, as well as any bearing that may have stuck to the gears
28 Space the shims and bearings as shown on a paper towel so they may be re-installed in the correct position
29 Remove the Bevel gear and shims from the top
30 Place the top shims on the top side of the towel, then the gear in the middle and any bottom shims on the bottom of the towel as shown
31 Remove the Anti Reversal Latch and spring
32 Set the latch and spring on the paper towel
33 Use pliers to remove the Tappet plate spring
34 Remove the spring from the Tappet plate
35 Remove the Cylinder assembly from the gearbox
36 Remove the Piston from the Cylinder
37 Remove the Tappet Plate from the front of the Cylinder
38 Remove the Nozzle from the Tappet Plate
39 Remove the Cylinder Head from the Cylinder
40 Clean all components with denatured alcohol and a toothbrush and paper towels. The Nozzle and Cylinder Head port can be cleaned with Q-Tips
41 You can remove the second tooth of the piston to prevent pre-engagement on higher speed setups, but this mod will work for all AEG’s. The second tooth is the one on the right side just left of the thick plastic first tooth and an Exact O knife can be used to carefully carve it out. I upgraded to a G&P White PolyCarb Piston with the second tooth removed and a G&P Explosive Piston Head without Bearing. Be sure to use LokTite on the Piston bolt when installing so it doesn’t work its way loose
42 Remove the Sector gear and set it on the towel
43 Remove any bottom shims
44 Place the bottom shims at the bottom of the towel
45 Remove the Spur Gear and place it on the towel
46 Remove any lower shims and place them under the Spur gear on the towel
47 Make sure all lower shims are removed from the bearings
48 Remove any upper shims and place them with the corresponding gear on the top of the towel
49 Shims in their position and gears are shown
50 Push the motor spring inward and lift the front of the motor by the Pinion gear
51 Remove the motor from the Gearbox. It is a good idea to put a mark on the top of the motor before removing so you re-install it in the same direction. If installed wrong, the motor wires will be reversed and the gearbox will not turn when assembled
52 Remove the Spring Guide Latch, latch spring and pin
53 While it is not necessary, you can remove the Trigger Switch by removing the two retaining bolts. You will need to re-align the switch during re-install, so yo may wish to leave it alone
54 Set the switch aside if removed
55 Remove all the excess gear grease form the gearbox with paper towels
56 Denatured Alcohol can be used to clean both Gearbox halves
57 Re-install the switch if it was removed, but do not tighten the bolts
58 Apply gear grease to the Spur gear, wiping a thin film on the top and bottom surfaces of the large gear. I use a small paintbrush with short, stiff bristles and lube the teeth of each gear. Wipe a very thin coat of grease on the shims and rub them between your finger and thumb, then install the bottom shims on the gear shaft. The thin coat will help retain them on the lower shaft. Install the upper shims, then install the Spur gear
59 Apply grease to the Spur gear and disconnect surface, then install the shims and gear in the same manner as the Spur gear
60 Apply grease to the Bevel gear and install the shims and gear in the same manner as the last two gears
61 Apply Cylinder grease to the piston rails and Tappet surface on the gearbox half
62 Repeat the grease job on the other gearbox half…Tappet area is shown being greased
63 Apply a thin, even coat of cylinder grease to the inside of the Cylinder
64 Re-grease the O-ring area of the Cylinder head and install the Cylinder part way. Place the Cylinder assembly temporarily in the gearbox and hook the gearbox post in the Cylinder side hole, then push the Cylinder on to the Cylinder Head until it is centered in the opening of the gearbox. If you wish to tighten the stock cylinder joint, you can wrap the Cylinder head with a few wraps of Teflon Tape used for sealing water pipes. Wrap the head so the tape is flush with the inner rubber surface, then install the Cylinder head, install in the gearbox and adjust the position, then use an Exact O knife and cut the excess tape flush with the edge of the metal Cylinder
65 Install the Nozzle on the Tappet Plate
66 Install the Tappet assembly on the Cylinder shaft. you can add a thin coat of grease to the Cylinder shaft before installing
67 Check the tappet and make sure it pulls off easily without binding
68 Install the Cylinder and Tappet Assembly in the Gearbox, making sure the Tappet plate rides in the molded slot in the Gearbox
69 Install the Tappet spring on the Tappet Plate as shown
70 Use pliers or a screwdriver to install the Tappet spring to the gearbox post and push it down so it is parallel to the bottom of the Tappet Plate
71 Use cylinder grease to lubricate the slots and O-Ring/Piston head grooves
72 Position the Spur gear with the teeth pointed down and the tappet button at 1 O’clock as shown. Install the Piston assembly into the Cylinder, making sure the Piston rails engage the gearbox rails
73 Install the spring on the motor. If you wish a high speed setup, the motor can be replaced with a G&P M120 Short shaft Motor
74 Install the motor, placing the Pinion gear under the Bevel gear and make sure the Motor spring is engaged in its slot. Also, make sure the motor is installed with the correct side up, otherwise the gearbox will not turn when power is applied
75 Install the Anti Reversal latch spring on the bottom shaft of the latch and hook it to the latch as shown
76 Install the Anti Reversal latch in the gearbox
77 Install the Spring guide latch pin in the hole in the gearbox
78 Install the Spring Guide latch spring as shown
79 Install the Spring Guide Latch, making sure the spring engages the upper part of the latch
80 Feed the red power wire from the Trigger Switch through the hole in the upper gearbox
81 Install the upper half of the gearbox, making sure the three gears, anti reversal latch and Spring Guide pin are aligned. A screwdriver can be used from the bottom of the gearbox to move the anti-reversal latch around until the top engages its hole, as it tends to be the most difficult part to get aligned. Also, if you removed the Trigger Switch, you may have to move it around until it aligns with the screw holes in the gearbox. Make sure the gearbox is installed flush along all edges. Check the piston to insure it moves freely inside the gearbox
82 Install the gearbox bolts and tighten. Do not forget to tighten the Trigger Switch bolts if you removed the switch earlier. It should be positioned as shown
83 Install the red wire from the inside of the gearbox to the motor terminal
84 Install the black wire to the motor terminal on the rear
85 Dress the wires as shown and install a new tie wrap, then trim the excess. Push on the Nozzle to insure it moves the Tappet plate in and out
86 Install the gearbox back into the receiver, making sure to feed the two gearbox wires into the forward battery area through the lower hole of the hatch
87 Install the charging handle over the spring shaft on the gearbox. Install the right side hatch bolt in front of the charging handle if it was removed
88 Install the two Gearbox mounting screws, push the gearbox forward until it stops and tighten the screws
89 Install the spring back in the Gearbox. I upgraded to a Mad Bull M110 Spring for my high speed setup
90 If you wish to upgrade to a Ball Bearing Spring Guide, remove the rear bolt at the center of the spring guide assembly, then remove the spring guide from the front of the assembly. Install a Version 2 Ball Bearing Spring Guide and then re-install the bolt and tighten it down. Install the Spring Guide assembly until it “clicks” in place
91 Drop the Hatch over the receiver and squeeze the two half moon buttons, then press down until it engages
92 Pivot the Rear Stock Door back up
93 Install the Rear Stock Bolt
94 Screw on the knob and tighten down the bolt
95 Re-install the wire harness to the two gearbox wires, then install your battery
96 Install the barrel into the gearbox, making sure the barrel is lined up with the slot in the gearbox and insure it engages and sits flush to the front of the gearbox
97 Install the outer barrel, pushing in and down until it “clicks” in place
98 Install your Box Mag and test fire the gun. This completes your M249 SAW Gearbox maintenance procedure 


Best Regards,

Carl Tulanko
Team Stormblade
Milsim Airsoft
Cincinnati, Ohio

Comments are closed.