broken spur gear

Discussion in 'Gun Building, Modifications & Repairs' started by Osvald, Jul 23, 2017.

  1. Osvald

    Osvald New Member

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    macroom
    i bought dboy scar h couple weeks ago i changed hop up chamber to cnc scar h hop up and after 800¬ shots it started to double feed triple feed make grinding noise until finally spur gear teeth broke all suggestions why did this happen would be helpful i dont want to make same mistake. and one more think i got spare shs 13:1 gears can i use them as new ones with all other parts being stock ?
     
  2. Sitting_Duck

    Sitting_Duck Well-Known Member

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    only the bevel "might" be compatible

    the ratio is mostly set by spur & sector gears
    so these two must be used as a set

    a 16:1 & 18:1 set use same type sector - the spur changes slightly
    (but "should" be compatible)

    bevels "usually" have 10 teeth to spur but you can get 8, 9, 10 & rare 11 teeth
    (think I have seen a 12 but don't quote me - 95% bevels are 10 teeth)

    The spur if broken will need to be replaced like for like
    the 13:1 spur has a larger inner ring or more teeth that mesh to sector
    & 13:1 sector will be different

    thus we normally suggest gear are replaced as a set
    you can switch & hunt around for one in a large spares box
    finding one that sounds &runs nicely if compatible

    ortherwise - just replace a new set

    the double firing etc does lead me to think you was running gun too fast
    if you go too nutz you get PME and teeth on gears or piston just strip
    if this was the case you need to ease up a bit on the juice
    (especially if you use the 13:1 set)
     

  3. Osvald

    Osvald New Member

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    macroom
    well i was using recommended 9.6v and stock motor the gears that broke were stock gears everything was stock when my spur gear teeth broke only the hop up chamber and bucking was new ones so i dont think gun running to fast was the issue, and i noticed one more thing that on new hop up bucking when i place a bb i barrely need to push in it just falls throu bucking lips to easy could this be the case of double triple feeding it just feels that mags push to much bbs into hop up unit ? and as for gears i have 13:1 set of gears for replacement i just cant fit in spur gear because of reinforcement
     
  4. Spoon

    Spoon Member

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    11
    Montgomery Creek/Redding
    I had the same problem with SHS 13:1 gears off eBay. Tried them in a couple V2s with different combinations of bushings/bearings and no matter what I did couldn't get the spur gear in and able to rotate. It was way too tight with no shims. I ended up putting them in a V3. I got some SHS 16:1 gears from Evike, the ones in a Matrix box (gears are labeled SHS) and they fit in all the GBs the 13:1 gears didn't work in.
    As far as breaking teeth off the spur, I'm not sure why that happens but it's happened to my neighbor's gun (completely stock running 9.6) It broke the replacement spur gear on the first test shot. I replaced the bushings and the spur gear, it works fine now. So, I'm assuming the cause of the problem was worn out bushings. It originally had slotted/oil retaining and I replaced them with solid bushings. Maybe you should replace your bushings as well.
     
  5. Osvald

    Osvald New Member

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    macroom
    well the problem why i cant fit spur gear is this part reinforcement [ame]https://www.youtube.com/watch?v=6ZMLjBSNFu4[/ame]
    and as for bushings they are pretty new but i noticed gearbox had very bad stock shimming
     
  6. Hangtight

    Hangtight Well-Known Member

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    447
    It sounds as if you might have pushed the hop rubber too far over the end of the barrel, probably when you put the barrel and rubber back into the hop chamber. If it was a tight fit then it would have stretched over the end of the barrel, opening up the diameter of the sealing lip. If this has put the mound on the rubber in the wrong place so it isn't lined up with the barrel window that would explain the multiple feeds as there will be no restriction at the hop window.

    If the shimming was bad then the chances are the gear teeth were only partially meshed. They really need the full width of the tooth to engage with the full width of the tooth on the corresponding gear, otherwise they'll just snap off.

    Please use capitals and punctuation in your posts. It's makes them so much easier to read!
     
    Last edited: Jul 23, 2017
  7. Osvald

    Osvald New Member

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    macroom
    well i changed hop up bucking rubber, now im waiting for new bearings to come.Im going to trim down that reinforcement part that gets in spur gears way and put it all back together from scratch and see how it goes then and by the way i forgot to mention my gun is only 1j if that says anything
     
  8. Sitting_Duck

    Sitting_Duck Well-Known Member

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    Ah - my first reading was gun was firing two shots on semi & seriously over-cycling
    eg: about 25rps which is easy to do on a high speed motor & 11.1v

    Re-reading it I'll take a stab again....

    Did the gun really double feed - most likely not
    if was misfeeding due to tight bucking lips or protruding bucking lips catching on bb
    the double occurs when first bb gets partially stuck and doesn't fire
    the second bb eventually chambers and two bb's come out
    but firing order wasn't 1-1-1-1 etc...
    but 1-0-0-2-1-0-2 etc....

    When the bb's were getting stuck it was sealing the piston's cylinder
    just like placing your finger over a bicycle pump or syringe or compression test
    Now with the end sealed the air can't escape normally when firing a bb
    The increase in compression is slowing the piston returning speed
    and if the piston doesn't return in time then PME takes place
    (just like going nutz @ 30rps without doing some homework)

    Most people - myself included do the beginners mistake:
    Got jam - fire some more - don't work then fire some more
    Still don't work - go nutz on auto - oops crap that don't sound good

    Nah - got jam, mag out, single shot only never auto
    half a dozen shots later - damn it, reach for jamming rod or disassemble

    [​IMG]
     
  9. Osvald

    Osvald New Member

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    macroom
    I think you are right thanks for good answer it might have been portruding bucking because i was trying flat hop up i guess there was to much hop up or smth and the bbs got stuck like you said and then instead of stop firing i shot couple more bursts and it broke