Gears Not Meshing Properly

Discussion in 'Gun Building, Modifications & Repairs' started by Sleeplessperson, Jun 30, 2017.

  1. Sleeplessperson

    Sleeplessperson New Member

    Fort. Campbell
    Hey guys so I recently got 13:1 SHS gears for my VFC VR 16. I had shimmed it and felt like it needed to be re-shimmed again after testing it. So I shimmed to the best of my abilities but it still makes a slight grind noise. I isolated the problem to the spur and sector gear. I decided to pull them out and see if they properly mesh, however I get resistance, like they get stuck due to the teeth not properly aligned on one of the gears. Has anyone had this problem?

    I tested the stock VFC gears and they do not have this issue, so I can only blame the SHS gears.

    Any help on this matter is much appreciated!
  2. Sitting_Duck

    Sitting_Duck Well-Known Member

    check how true the axle is on each gear...
    some bad sets (not SHS) have had a pi$$ed axle
    set at like 88 degrees instead of 90 so the gear itself runs buckled

    examine each tooth at back of sector & inner ring of spur for chipped teeth
    or a bad burr

    check sector on its own - if shimmed too high below the sector
    the tappet lug can rub against the shell on the top
    check this, if the cam/lug rubs you may need to mod/sand the box
    (if you can't alter the shimming to respace the sector)

    you have narrowed it down a little to those two gears perhaps
    now see if you identify the exact issue - likely to be one of those gears

    In extremely rare cases a 12:1 spur could have been supplied with a 13:1 sector
    the spur inner teeth on the 12 will be larger
    and the sector on 13:1 will have a larger ring of teeth
    these together may not be compatible as they will try to push the gears apart

    Could have a moody set
    could be the way the box/bushings are set they just slightly bottom out on the teeth

    I have noticed on some boxes and gear sets the bevel gear can sometimes sound rough - sometimes swapping out a stock or similar 10 tooth bevel as most gear sets still use regular 10 tooth bevel gears
    On noisy sets, I remove the bevel and ensure spur+sector run smooth then try another bevel
    In your case you have done this but the spur+sector is the issue

    bad chipped/burr on teeth or bent/pi$$ed axle comes to mind
    check the allen key bolts are done up correctly and axle not crooked

    EDIT: afterthought....
    SHS gears are very chunky and often the spur gear if set very low
    can rub on both bevel & sector bushings underneath
    This doesn't happen on smaller 6mm bushings
    kind of very very lightly scrapes on 7mm bushings
    but on larger 8mm & deffo on 9mm bushings they will rub if spur gear is set too low on deep bushings


    actually think this is cut off lever rubbing on bushing if I'm honest
    the gear rubbing produces and opposite arc or convex/concave point of wear
    but you get the idea that a deep bushing on bevel/sector can rub on the outside edges of spur


    check see how low the spur gear is set underneath & if gears run true & spaced ok
    Last edited: Jun 30, 2017

  3. Sleeplessperson

    Sleeplessperson New Member

    Fort. Campbell
    Thanks for the pointers but sadly nothing will work. I took the gears off and meshed them by hand at every type of angle and nothing. Oddly enough when I take a VFC stock and mix then it meshes fine... My last resort is to get a different set, maybe just throw in 12:1 gears instead...


    So I decided to clean the gears with soap and hot water and brushed them. I meshed them a few times and they are better but still not what they should. Should I risk the gears and run with it for a while?
    Last edited: Jun 30, 2017
  4. Sitting_Duck

    Sitting_Duck Well-Known Member

    Hmmm, I'd probably not tbh - depending how rough/smooth they stil run
    you could "run them in" but only by hand spinning them
    rough running under power/stress will promote wear in bearing/bushings

    TBH - I'd order either a new set maybe try a ZCI/Core set of 13:1's
    personally I have rated SHS over Core/ZCI as the bevel isn't great
    but you probably could use the SHS bevel if it runs well/better

    What is your old gear set ratio ?
    I had an old VFC box that had quick 16:1 gears in
    doesn't the spur & sector have a spring on them?
    anyway to quickly find your gear ratio.....

    chuck all 3 gears in the open box
    set the sector's first tooth at say 12 o'clock
    mark with pencil the bevel at 12 o'clock
    rotate the sector gear carefully 1 full complete revolution
    counting the bevel turns as you go....

    multiply the bevel turns by 3 to get you gear ratio

    eg: 6.25 bevel turns = 18.75 which is the actual ratio of 18:1 gears

    I had a vfc set which came out at 5.5 = 16.5:1
    most 16:1 sets are 5.75 = 17.25:1 ratio so vfc set was a touch faster

    12:1's work out at 4.25 = 12.75:1 ratio

    your old set might not be that slow is what I mean so you could stick with those

    or try another 13:1 set and see if that runs smoother
    possibly might be able to mix & match the two 13:1 sets
    BUT this should not be done unless you are still having grief
    and only with paying very very close attention to how compatible they are

    You should not really mix sets of gears as a rule of thumb
    but bevels often can be used if they mesh/run ok
    and 18 & 16:1 sectors are usually the same & compatibleif you check carefully
    hence if you get another decent 13:1 set the spur/sector have a chance
    you might find you need to experiment or mix/match

    could of got a defective or cheapo snide fake set of gears
    I got a couple of fake "pink" shs m4 nozzles that was wrong length and just didn't fit on tappet or cylinder head correctly
    You could order another shs set from elsewhere to avoid same issue from similar batch perhaps

    Sorry I can't offer more help, I'd say try the shs gears in another box if you have one lying around & if still no joy contact the seller/retailer
    Sucks but bad batches, fakes and just simply some stuff just works great in some builds and other stuff in some builds just don't seem to run so sweet as expected
  5. cetane

    cetane Well-Known Member

    Markham & Stouffville, Ontario, Canada
    The shs 12:1 & 13:1 share the same sector gear. The difference between the 2 is the spur gear on the step gear that interfaces the bevel. It uses the same size/tooth count as a 16:1 set
  6. Sleeplessperson

    Sleeplessperson New Member

    Fort. Campbell
    Thanks sitting_Duck for the help! I have just accepted its the gears after borrowing my buddies 13:1 SHS and they don't seem to have this problem. I think I'll just go for some ZCI 13:1 instead, from what reviews say they are quality gears.
  7. Sitting_Duck

    Sitting_Duck Well-Known Member

    I stand corrected, it seems the spur's outer teeth is what alters on the 13 to 12 gear sets
    cheers for putting me straight on this & about sector gears are the same
    (should be able to use either a 12:1 and/or 13:1 sector if I over Short-Stroked the original high speed sector or sector busts)