Best way to center sprocket ?

Discussion in 'Transmission / Drivetrain' started by ezrider, Aug 13, 2016.

  1. ezrider

    ezrider Member

    [​IMG]

    Is there an ideal way to centering these things? Seems when you go around tightening these bolts, the sprocket starts shifting for some reason.
     

  2. Frankfort MB's

    Frankfort MB's Well-Known Member

    I feel ya, I've never been able to get one perfect.... I have a buddy who used to build MBs that was good at doing them. If I talk nice too him I can get some help:D
     
  3. crassius

    crassius Well-Known Member

    put in all 9 loosely, tighten every third one, using an old drill bit (or similar) that fits between teeth & is a bit taller than teeth smack the sprocket down on the high side until it is centered in up/down direction

    then tighten all bolts as much as possible (checking every so often that up/down stays put) - adjust wobble by fitting a large crescent wrench over sprocket and pushing in or pulling out until wobble is gone
     
  4. ezrider

    ezrider Member

    I tried putting in two screws along either side of the hub axle while tightening the bolts around, but the sprocket still shifted a quarter inch off center. You can definitely notice the chain slack variation.
     
  5. CrazyDan

    CrazyDan Member

    Best advice I saw was to spin the wheel on the bike while the sprocket was loose enough to move a little to center it. I like to tighten every 4th bolt a half turn each once it begins to get snug to spread it out a bit more, doing every 3rd is still hitting relatively the same side as the last bolt. Tightening these rag joints down with no wobble can be considered an art :p. Tackle it like you would truing a slightly bent rim. Patience goes a long way. Good luck.
     
  6. ezrider

    ezrider Member

    I'll keep these tips in mind, when I mount it on the Mongoose. Thanks.
     
  7. Nate888

    Nate888 Member

    if I'm seeing this right on my mobile screen here, the wheel hub looks big enough that one of the 2 piece sprocket mounts that clamps onto the hub would probably fit. I have one of those & it's pretty solid & hassle free once you get it installed firmly in place ( don't over torque-we're talking steel bolts into aluminum here, & after your first test run is good, reinstall the bolts using blue lock tite)
     
  8. Steve Best

    Steve Best Active Member

    The standard sprockets "register" with most wheel hubs.
    That means the hole in the sprocket fits most hubs quite well, within less than a mm.
    So what about all the wobble?

    You have to tighten the bolts progressively in a manner that brings the sprocket true.
    Tightening them all up to X inch/pounds torque will not assure a true sprocket.
    Install the sprocket loosely, then mount the wheel so it spins.
    In the photo below I am using a dial indicator but you could also use a piece of wire wrapped around the wheel stay:
    [​IMG]
    So you tighten the bolt and nut nearest the pointer to get rid of the high points on the sprocket.
    Go around and around, ideally doing every 3rd or 4th bolt, or looking for the high points and tightening them up, little by little until the sprocket is true and tight. The same thing can be done for concentric if the register is too free. When the sprocket is barely snug, point your wire or indicator at the sprocket teeth and spin it around looking for the high point. Tap it down lightly with a hammer and check again. If it is better, tighten the bolts a bit and check again. Repeat until tight and true.

    Steve
     
  9. zippinaround

    zippinaround Active Member

    Search on ebay for dial indicator can get one for about 5€ delivered I didn't get mine yet but will make a holder of sorts for it when it comes
     
  10. KCvale

    KCvale Motorized Bicycle Vendor

    The very first I do with a new sprocket is see if it is true on a flat surface, or warped to begin with.
    A warped sprocket will never be true which is what leads to chain jump problems, it's not uncommon, I must have 40 warped sprockets on my shelf.

    That looks like a coaster brake wheel.
    Make sure there is no dist cover in the way and the sprocket can fit over the hub.

    Now eye up your rear sprocket chain line to the engines sprocket to see if you need to cup it in or out.
    It really bites if get this wrong and have to flip it.

    Sandwich it up, then get all the nuts firm and centered the best you can by eye.
    Start with bolts through where the inside plate pieces meet.
    You want them to form a perfect circle, not overlapping or offset.
    I like a deep 10mm socket and my hand drill to get everything firm but movable.

    Next you are going to need a truing stand that will hold the wheel and allow it to spin.
    For me that is just a front fork upside down in my bench vice.

    [​IMG]

    Mount your wheel in the stand and give it a spin.

    Look directly at the sprocket face and see if goes up and down by just focusing on something through the spokes, like a spot on the wall, and you can see it.

    If you can see it going up and down catch it the highest point at the top.
    Now get yourself a short piece of chain and lay it in the teeth at the top.
    Get yourself a hammer and tap the sprocket down just a little.
    Take off the chain and give it another spin.
    Repeat until it is true as that is what causes chains to get loose, then tight, then loose...

    Now to tighten it up while you get any wooble out...

    Look from the edge of the sprocket for back and forth wobble.
    Start tightening up the nuts where it wobbles to the outside to pull it in.
    This takes awhile with lots of spins but that is what causes chain jumps.

    Hope that helps ;-}
     
  11. ezrider

    ezrider Member

    Not cheap, but I think I found the ideal way to center a sprocket:

     
  12. Nate888

    Nate888 Member

    that's what I use & I can confirm it's centered every time, although you need wheels w/ big hubs that are strong enough
     
  13. KCvale

    KCvale Motorized Bicycle Vendor

    Yep, the 'clam shell' mount is usually for a fat coaster brake or internal shifting hub, or something other than 36 spokes.
    Just MAKE SURE it's tight around the hub, if it gets loose it will take out every spoke on the left hand side that will result in Catastrophic failure of the really UN-friendly nature.
     
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