Front Sprocket Replacement

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Removing or replacing the front sprocket on S and X platforms.

Video Guide

Some guidance from Terry in this motor removal thread:

  • Basically, if you are doing this to try to get more acceleration by moving from a 28 tooth to a 25 tooth, Harlan recommends trading in the DS on a 2015+ SR or 2016 DSR if you need the off road capabilities. You will get much much more acceleration and not hurt your top end performance.
  • On the drive belt side, the upper rear 5mm bolt takes extreme care to remove. It is tapered to locate the motor. There is a very strong chance of stripping the head and have to drill it out. Make sure to have a machine shop close by just in case.
  • On the other hand, removal of the motor may not be necessary.
  • The other 7 bolts, 3 on the sprocket side and 4 on the rear brake side are the only thing simple and straight forward.
    You will need a special 3" or longer 6mm allen head socket for sticking in the hole through the frame at the front of the motor.
    1. Remove the rear brake pedal and assembly to get the heel guard out of the way of the top right rear motor bolt.
      Be careful not to strip these bolts either.
      They have Loctite; use a torch.
      And make sure your local hardware store has these replacement bolts handy in case you have to drill them out.
      The rear brake pedal needs to move anyway to get the right swingarm bolt out.
  • Also the sprocket bolt itself, as well as removing and installing the new sprocket on the shaft can be very difficult. Some of the best professionals have had trouble.
    Loctite has been used on everything and you will need a torch to remove them.
    Even so, you will need a strap wrench with an old belt as the strap to hold the sprocket and a high power impact wrench.
  • Even with all that right, you have a chance of stripping or breaking the bolt. The sprocket is pressed pretty tight.
  • Be very careful not to permanently damage the motor bearings by prying between the motor itself and the sprocket to try to remove it, and also by tapping with a hammer to try to fit the new one on. You will be tempted to do both, but you need to find another way.
    A gear puller would be much better.
  • There are other things to watch for:
    • Mark your phase leads and pay special attention to the routing.
    • Don't over-tighten the motor jack nuts and bolts until you have the swingarm back in place as it can pull the frame together slightly making it impossible to get the swingarm in place.
    • Make sure you unplug the 8 way motor encoder harness and it doesn't get yanked and pull a wire.
    • The top shock mounting bolt is a 15 and 17 mm and can be done with ratchet wrenches 1/32 of a turn at a time, or without ratchet wrenches if you are known to have extreme patience. It can take a while. The 2014 is a little easier and is (seems to be a) dual 17mm bolt and nut.
    • The swingarm bolts are 10mm allen head and can be extremely hard to relocate even when working with someone else, a rubber hammer, and a flashlight. Those who have replaced their own belt before can vouch for this.
  • Again, I doubt too many on this forum have done this, and those who did I'll bet agree with me that it makes more sense after they did it and perhaps had their bike out of commission to work through the things that didn't go right, and would agree to just upgrade to the SR or DSR first vs trying to change the front sprocket.
  • Also the 25 tooth sprocket will break belts easier as less teeth are engaged than the 28 tooth, which can make it more likely to sheer teeth in the event of a wheelspin, and it bends the belt at a sharper radius which can possibly fatigue the carbon strands more. The SR actually uses a 30 tooth front sprocket which is even nicer to the belt than the 28 tooth.