A&K SR-25k Gearbox got borked by Guarder SP150

Discussion in 'Gun Building, Modifications & Repairs' started by HourlyB, Apr 16, 2021.

  1. HourlyB

    HourlyB Member

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    Yep.

    Guarder spring kinda busted the gearbox shell. Not like it was terrific in the first place.

    Any suggestions on a replacement shell? I'd prefer something that uses a VFC or KWA tab allignment style spring guide instead of the small pin one that the A&K uses. Retro Arms is expensive, but seems to tick most of the boxes, but I don't know if it's compatible with the A&K SR-25K body.
     
  2. aotsukisho

    aotsukisho Well-Known Member

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    I have a Classic Army AR-10 (garbage btw) and JG SR-25 shell that both accept the CA and Retro Arms v2.5 gearboxes with minimal modification (some grinding in the RA mag release hole). I wouldn't imagine your A&K unit being too different.

    [​IMG]

    I run an M140 in the CA (after radiusing) and an M170 in the RA and haven't had problems yet, both of them are QSC style so the spring guides have wide flat tabs.
     
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  3. HourlyB

    HourlyB Member

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    Gotcha.

    Not entirely related, but would you suggest I upgrade the gears to a Seigetek set since I am using the Guarder SP150? Right now I have a set of SHS gears.
     
  4. aotsukisho

    aotsukisho Well-Known Member

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    Not sure if that's necessary, I actually run SHS gears in both of the builds. The CA gearbox actually temporarily housed a SHS DSG with M170 lol
     
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  5. 1tonne

    1tonne Well-Known Member

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    I got a Retro Arms A&K gearbox for my JG and it worked a treat. A little modification but works well.
    The one thing that is annoying is that the front of the GB is extra thick. This means that the tappet plate will not travel as far forward as it should do and this means that you will most likely get an air leak between the nozzle and the bucking. I grinded the front of mine down to normal thickness to get the tappet plate in the correct position.
    I also know of another person who had to do the same.
    It is a big pain in the butt
     
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  6. HourlyB

    HourlyB Member

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    So these gears should be fine for a SP150?

    Dumb question, but is it just a issue with the shell in general? Like irrespective of the original manufacturer that's going to be a issue with the tappet plate
     
  7. 1tonne

    1tonne Well-Known Member

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    Yes it is. Great shell once it is fixed but if you have no "know how", I would not advise getting it. Took me a couple of hours to get it right because you have to be very careful.
    I did email retro arms and tell them but they did not respond and so I would say the issue is still there.
    They made it thicker because everyone thinks that a thicker front end will not break off but in reality, it can make leaks and feeding issues.
     
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  8. HourlyB

    HourlyB Member

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    Any suggestions for a replacement?

    I really don't want to buy a A&K one given how the first one just gave up.
     
  9. 1tonne

    1tonne Well-Known Member

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    It is normally the front end of the gearbox that breaks off. I am guessing that is what happened in your case too. You could get an A&K replacement and then use a Mag Well Brace to support the front of the gearbox. An M150 is not that big and so it should work well. And the A&K GB's are cheap as.
     
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  10. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    There is a reason why A&K mechbox are cheap and that is what suffers from manufacturing, quality. Get one batch that isn't cooled/mixed right and it's more brittle than another batch that would be rather durable.
     
  11. HourlyB

    HourlyB Member

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    Gotcha, but I really dislike the overall design of the gearbox itself. Reassemling it is a royal pain, and I think the reason it bowed out like that is because parts got shifted around and prevented it from closing.

    Seems like it. But if what 1tonne is saying, a Retro Arms shell will be trading mold for mildew.
     
  12. aotsukisho

    aotsukisho Well-Known Member

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    Making minor modifications to fit an indestructible shell doesn't sound like a bad deal to me
     
  13. 1tonne

    1tonne Well-Known Member

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    I may have worded it a little wrong. The mod is not that minor. You do have to have a good head to make sure you do not stuff the GB when grinding at the front. Sure, most people will get it right but there will be some that would make the front too thin.
    After grinding the front, I have mine at 3.3 joules and it is fine.
     
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  14. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Thus this mechbox seems far from drop in "TM" compatible. Sounds like a 4th Uncle Twice Removed...
     
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  15. HourlyB

    HourlyB Member

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    Would there be any other solutions? Switching out the hop-up, maybe? I was going to get a Maxx ME Pro chamber installed.
     
  16. 1tonne

    1tonne Well-Known Member

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    No. The only solution is to grind the inside of the front of the GB so that the air nozzle can go far enough into the bucking. A different hopup will not work. Nor will a longer air nozzle. A longer air nozzle would seal better but it will not move back far enough to allow for the bb to go into the hopup.
    So really, Retro Arms should be refunding everyone who purchases an SR25 gearbox.
    I did contact RA about this and they did not respond. So I do not mind telling everyone about this issue.
    But like I say, if you have a bit of know how, then you are onto a winner.
     
  17. HourlyB

    HourlyB Member

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    I bought a RA gearbox and a set of 8mm FLT bushings

    The bushings don't fit. They are the same size as the gearbox holes.

    I hate this fucking gun.
     
  18. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    EU Mechbox and Taiwanese (perhaps) made bushings not playing nice. Looks like you will need to get the bushings made by RA too.
     
  19. 1tonne

    1tonne Well-Known Member

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    The RA bushing are extra, tight. Once in you will never get them out.
     
  20. Peeque

    Peeque Well-Known Member Supporting Member

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    I believe the bushings are meant to be press-fit into the shell. That's what I did with mine. Also F.L.T in an RA gearbox.