JG SR25 6652M is driving me crazy, need some good advice.

Discussion in 'Gun Building, Modifications & Repairs' started by BoogerMc, Jan 6, 2013.

  1. BoogerMc

    BoogerMc Airsoft Jedi Master Supporting Member

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    A customer bought this gun for his son.

    http://www.airsplat.com/Items/ERM-JG-SR-6652M.htm

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    When they brought it to me, it did not work, the battery connector was "broken," one of the wires popped out of the plastic outer jacket. Fixed that.

    The customer stated the gun fired itermittenly and made some horrible noises. I opened it up, the sector gear and the metal teeth on the piston were worn and would jam, locking the gearbox. Fixed that, replaced the gears and piston with SHS 32:1 high torque gears and an SHS piston with full metal teeth.

    http://www.airsoftstation.com/shs-32-1-gears-ultra-high-torque-airsoft-aeg-gear-set.html

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    http://www.airsoftstation.com/airsoft-shs-full-steel-teeth-tooth-piston-ver-2-3.html

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    After replacing these parts, the gun would not cycle at all, it was locked completely. I even blew the fuse trying to get the motor to turn. Luckily, I didn't blow the MOSFET. Turned out there was a tiny piece of metal in the gearbox body that was interferring with the sector gear. This is part of the gearbox shell, the trigger assembly rests up against it, so to speak. However, as far as I can tell, it has nothing to do with the operation of the trigger assembly, it's just there as a place holder. So I ground it down a bit and the sector gear turned freely, mind you, I only ground a few microns off of it, just enough to get the gear to clear, but not enough to affect the integrity of the part or the shell.

    However, when I reassembled the gearbox, it was still locked. Another mystery to solve.

    This time, the piston teeth were interferring with the full teeth set of the sector gear. It seems that with this particular gear, one needs a half-tooth strip, not a full-tooth strip because the full teeth and the partial teeth are the exact same diameter. So, I ground off half the teeth all the way down the strip. Put it together again and it worked perfectly.

    Well, almost.

    Now the gun will fire just fine in full auto, but in semi-auto, it will intermittenly fire full-auto or semi-auto. For example, if I pull the trigger back quickly and hold it, the gun fires once. If I do it again, it fires once again; however, if I fire again, the gun goes full auto on me. Then again, it will sometimes do this the first time I fire it after giving it a short rest. I thought perhaps it was the MOSFET, but I do not think this gun has the variable fire selection (although I could be wrong). I checked the forums, found several threads, tried all the suggested fixes, including checking the selector plate alignment, the selector lever appears to be working fine, and everything else thus far; however, I have not checked the trigger contact switch, although it is working properly, as far as I can tell.

    At this point, I'm stumped, fed up, frustrated, and just plain done with it.

    However, I must get this thing fixed, I've had it almost three weeks and this isn't the only issues I've had. For example, when I first got it, thinking it was a standard SR25, I ordered the gears and piston for an SR25. Then I found the SR25 thread and realized the JG gearbox was not standard SR25, it is in fact just a standard V2 gearbox with some minor differences, but not in the gears and piston.

    Therefore, I had to order another set of gears and a new piston (and shims because I forgot them the first time around). Therefore, I have these parts and no gun in which to install them.

    http://www.evike.com/product_info.php?products_id=30841

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    http://www.airsoftmegastore.com/537...Steel-Gear-Set--SR-25-Gearbox-Compatible.aspx

    [​IMG]

    With all this in mind, I come to you, the denizens of this airsoft community. Please help before I tear what's left of my hair out. Any ideas why this gun is so stubborn, why it is firing full auto in semi-auto mode, and if anyone has any expereince with this gun, any tales or issues I should be aware of, for future reference.

    Thank you in advance.
     
    Last edited: Jan 6, 2013
  2. EDI1st

    EDI1st New Member

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    Did you check the cut-off lever and the spring?
     

  3. BoogerMc

    BoogerMc Airsoft Jedi Master Supporting Member

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    Yep. As far as I can tell the lever is fine and the spring is the original; however, it does seem rather weak, would replacing it with a stronger spring help or hurt?
     
  4. EDI1st

    EDI1st New Member

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    That probably is the problem.
    Replace it with a new/stronger one.
     
  5. Ehudakineyah

    Ehudakineyah New Member

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    Damn those pistons are over priced :/ lol. Make sure the piston is light too lol. Looks to be a standard milled aluminum piston that has been Swiss cheesed already. Hopefully it's less then 18 grams.

    I'd stock with a standard SHS 15 steel tooth piston :) can handle pretty much any spring. Easily Swiss cheesed :)

    As for gears, the SHS ones work just fine :) standard type gears for the JG SR-25 :)
     
  6. BoogerMc

    BoogerMc Airsoft Jedi Master Supporting Member

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    Ehudakineyah > The first piston pictured is not metal, the second one is, but I used the first because the second is too long. Same with the gears, I used the first ones pictured because the second ones have too many teeth.

    ED11st > I'll give that a shot. I've torn this gun apart more times than I care to count right now, what's one more disassembly. :D
     
  7. BoogerMc

    BoogerMc Airsoft Jedi Master Supporting Member

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    Thanks to all who helped, it turns out the spring was the issue. I found a spare, replaced it, and the gun is working fine. I will have to stock up on some of these from a local supplier as many of the springs seem weak to begin with. Again, thanks for your help.
     
  8. EDI1st

    EDI1st New Member

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    Just go to a hardware store and get springs of the same diameter.
     
  9. BoogerMc

    BoogerMc Airsoft Jedi Master Supporting Member

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    Yeah, that's what I was going to do.

    By the way, the gun is shooting 360 fps, 8 rps, and 1.5 joules with what I believe are .25g bbs. No idea on distance as I tested it on my range in my basement and that's only about 15 to 20 feet shooting distance. I also checked the sites with a bore sighter and they are dead on at this distance.

    Now just gotta wait for the customer to pick it up. The piston was $14.85 and the gear set was $28.50 with $12 shipping. I charged $10 for the bench fee and $10/hr @ 3 hrs for labor because of all the issues this thing gave me. With tax the total was $101.55 (I do this through my company, so I have to charge tax because the state has to get theirs, you know). The customer paid me $100 up front, so I'm just calling it even and eating the $1.55 (plus the cost of the other parts, but that was my mistake for not researching the gun better).

    Does this seem fair or excessive for a repair job?
     
  10. Ehudakineyah

    Ehudakineyah New Member

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    Seems fine for the work hours put in.

    Atleast you're only eating $1.55 lol.

    Sometimes jobs/labor becomes free with too many technical problems lol
     
  11. EDI1st

    EDI1st New Member

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    40 for swapping parts and tuning. It's fine


    8RPS LOL
     
  12. BoogerMc

    BoogerMc Airsoft Jedi Master Supporting Member

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    Yeah, 8 is a bit low, but based on what the father said when they dropped the gun off, I think he'll be happy with it. The father that is.
     
  13. EDI1st

    EDI1st New Member

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    Yea. But the trigger response is not DMR friendly at all lol
     
  14. BoogerMc

    BoogerMc Airsoft Jedi Master Supporting Member

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    I was thinking more along the lines of safety, according to the father, he thinks the reason the gun "broke" in the first place was because his son just wails on it in full auto, and I mean like minutes at a time. I'm thinking he might have worn the gears down prematurely because of this.

    As for trigger response, it seemed fine to me, about as good as any of my own guns. All-in-all, it's a fairly nice gun, just stubborn as all $hit. I have to admit I do like the way the body slides together and having the MOSFET makes it possible to switch to a lipo easier. The gun came with a large type 8.4v 1500mah NiCad, but I have recommended they upgrade to a NiMh for now. I think the kid needs some learning time before he gets too into the sport. If you know what I mean.

    I invited them to play at one of our games, but I don't know if the father thinks his son is ready yet. He says they mostly do backyard skirmishes, and his son has the "best" gun among his friends. I gather he meant they have cheaper or lower quality guns.

    Anyway, I sent an e-mail to let them know it was finished and ready for pick up, but haven't heard from them yet.