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Locking Gears A&K m249

3K views 10 replies 4 participants last post by  BoogerMc 
#1 ·
My m249 PARA I bought used has been having trouble ever since I bought it. It was intermittently locking for the last two months, but one day the motor burned out. It has been consistently locking up since I installed a Prometheus m120 spring, a G&P m120 high-speed motor, and a new trigger switch(original was cracked). I left the original gear set. I am fairly new to gearboxes, but nothing obvious seems to be the problem. I have checked the batteries, my 9.6v NiMH is working fine, and the motor itself seems to work fine as well. I have tried to shim my gearbox properly, but as this is my first gun to need tech work, I do not know what exactly to do. I have also cleaned and greased the gearbox, this has helped some. Any ideas?
 
#2 · (Edited)
I suggest you try to reshim it again using the bevel to pinion method. I'm assuming the gears are shim too tight which may cause the lock up. Make sure there are a little movement for the gear but not too much. I normally leave my gears with a small movement of 0.1mm. I also suggest that you might get a less powerful spring since the g&p is a high speed motor and the m120 is really pushing it. A m100 is what most high speed motors should use. If you have the money, go with the shs high speed or lonex a1 instead since they are way more powerful than the g&p and uses neo magnets.
 
#3 ·
As kind of an expert on this gun, I would suggest going a different route, replace the high speed motor with a high torque and stick with your current spring. I suggest either an SHS or ZCI motor, a Lonex A2 Orange is also good but pricey and the other two can be found much cheaper and do the same job. As for shimming, these gearboxes are a little more difficult to shim because of how they are designed, but they're not impossible.

Start with your motor in position, set your bevel gear in place, and check for clearance issues between the bevel gear and the motor's pinion gear. You should also check motor height adjustment at this point, too. Add shims as necessary to the bevel gear between it and the gear box. Once you have this adjustment aligned, remove your motor, close the gearbox shell with the bevel gear in place and check for gaps between the bevel and the other half of the shell. Add shims as necessary, but do not over shim, leave a small amount of play, about one to two sheets of notebook paper.

Once you are happy with the bevel gear, add the spur gear and shim and adjust until it is aligned, including closing the gearbox and checking for clearance and tolerances. Each time you close the gearbox, check the gears to see if they spin freely and if they shift side to side. Repeat the process for the sector gear.

Mind you, you do not need nor do you want any other components in the gearbox while shimming, they will only interfere and make things more difficult. Also of note, use SuperLube instead of Lithium or silicone oil or grease, it is much better and lasts much longer. You can generally find it at ACE hardware and sometime Walmart, you can order it from Walmart online. You want the gray tube that reads Synthetic Lubricant under the brand name. Use it on the gears and the piston slide, but do not use it inside the cylinder, use silicone grease or oil in the cylinder.

I also suggest correcting AOE with sorbothane and piston tooth to sector gear alignment modifications. These will greatly improve your gearbox's performance.

Hope this helps, and if you have any further questions, feel free to ask.
 
#4 ·
I'm not surprised it's locking up, the G&P M120 has very little torque and most smaller ni-mh batteries have a pretty low output. The motor might be able to pull the M120 spring with a higher output battery, but I wouldn't expect it to last very long and I highly doubt the trigger switch would handle the current very well.

I agree about replacing the motor with a neo magnet motor with more torque, but I do not recommend Lonex motors at all. The ZCI and SHS high torque motors gets the job done very well at a low price, or you could consider an ASG motor from Brill, they are similarly priced as Lonex, but are higher quality. If you can find a Guarder Infinite Torque Up in stock somewhere, then I can highly recommend that motor, I'd choose it over any of the other recommended motors.

You should consider making the transition to li-po batteries, you'll find that they offer significantly higher performance at a lower price and are actually more reliable than ni-mh batteries despite being slightly more volatile.
 
#5 ·
Lefse, I must disagree with you on one point the trigger switch in an A&K M249 can handle quite a bit of amperage and voltage; after all, they're rated at 15 amps at 250 volts AC and the one in my M249 and my M60 handle a 7.4 volt lipo without a MOSFET just fine. Although I do agree that the stock switches are just junk, period. They have a tendency to magnetize and remain closed, which is why I always replace them with a better model. I get mine at Mouser Electronics.

http://www.mouser.com/ProductDetail...GAEpiMZZMumBvQ1hY/fBT/NxSgnZxL/HAW0CET%2b7Oo=

Another option is GC Electronics model #35-844, but they're a lot more expensive.

http://www.gcelectronics.com/order/product_search.asp

Otherwise, Lefse, you're spot on.
 
#6 ·
I stand corrected, better safe than sorry though, I tend to over engineer things to have some head room.
 
#7 ·
Can you give me specific names or links for each of the motors? I would like to get the ASG, but I have found several different types. I want to get as much ROF as I can, but I don't want to have another useless high speed motor.

This one seems good,

http://www.evike.com/products/52190/

but I'm new to upgrades that actually require purchases so IDK.

Thank all of you very much for submitting such good advice!
 
#8 ·
That motor will get the job done, but will pull a lot of current since it's really a high speed motor. You will need either a huge capacity ni-mh battery or a li-po battery. If you want high ROF you may need to do extensive work on the gearbox depending on exactly how high ROF you want. Anything above 30rps and you're venturing into the area of advanced gearbox mods. Above 40rps and the laws of physics start to get annoying.
 
#10 ·
I have battled with the laws of physics before, a good tech always finds a way to work around the laws of physics. :D
 
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#11 ·
Hey, if I can build a DSG M249 (or the basic equivalent), then high RPS is more than doable. Now if I can just get an accurate reading on that damn gun. Still can't get a single mag to feed it properly. I'm starting to think it's the air nozzle moving too fast or not far enough/long enough to allow proper feeding.
 
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