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What motor does the 7 tooth D bore sprocket for #25 chain fit on?

I noticed 7 tooth D bore sprockets for # 25 exist and they are for sale online.  What motor do these mount on?  I am wondering if that motor will fit on the E-100 so I can use it instead of the stock motor with the 9 tooth motor sprocket.

Also, is there any way if the D bore is too small on this 7 tooth sprocket, to make it larger to fit on the stock E-100 motor?  Can I take a dremel type tool and very slowly and carefully nip out a new larger D bore or would I have to take this to a machinist to get it done?  I think 7 and 55 tooth sprockets would be almost ideal for offroading because it would drop the top speed from 10 mph to about 6.6 mph (to about 2/3rds of stock speed).  That is very significant and should help greatly.  Thanks for any helpful info.

We do not currently carry the 7 tooth sprockets for #25 chain so I do not have one to measure the ID of and know what motors it fits. It is such a small sprocket that I do not think it could have a 10mm bore and could only have an 8mm bore which is the right size for the E100 motor. 

Motor sprockets are hardened which makes grinding on them difficult, however, it may be possible to grind or have it machined to have a larger ID.  

The sprocket is 6mm and is advertised on Ebay for electric motors but doesn't specify which.  I would like to know what motor has a shaft compatible with this sprocket.  My E300s currently has 9 and 89 sprockets on it but could use even more reduction for riding on grass so I would like to try this 7 tooth.  I'd be willing to change the entire motor if it is similar in power and input voltage but if not, I am wondering if it is possible to just change the motor shaft to accommodate this sprocket.  It is a shame they don't make more sizes of front sprockets compatible with the E-300s and other similar electric scooters.  9 front is not small enough for me and I am already close to the max size that will fit on the rear (89 teeth).

On the Razor E300 scooter, the section of the shaft where the sprocket mounts has a 10mm diameter and is 8mm across where the flat spot is. 

That is not what I asked.  I am asking what electric motor has the shaft I need to fit the 7 tooth sprocket because it may be easier to just change motors on the E300s to get the reduction I desire.

Unfortunately, we do not carry a 7 tooth sprocket so we do not know what its interior diameter measurements are. If it has a 6mm bore as indicated on the photo then we do not carry any motors that have a 6mm shaft. The motors with the smallest shafts that we carry are 100 Watts and where the sprocket mounts they have an 8mm diameter shaft that is 7mm across where the flat spot is.

Let's assume the 7 tooth sprocket is 6mm bore with 5mm where the flat spot in the D bore is.  I wonder if a machinist could make that work on the E-100 scooter which I think has an 8mm shaft diameter with a 7mm "flat spot".  I would have a use for such a modified sprocket cuz I already am running the largest possible rear sprocket on the E-100 which is 55 tooth (with a 9 tooth front sprocket).  Going to a 7 tooth front (7-55) would be roughly equivalent to 9 and 71 sprockets.  Even getting an 8 on the front would be like having 9-62 sprockets.  There is very little clearance for turning right with the 55 tooth rear so at this point, my only options are to try to get a smaller front.  It is for kids learning to ride so low speed is better for them.  Also cuz they are still using training wheels and riding on a patio so it is better to have a lower "push off" speed requirement for them to they can take turns without the motor cutting out on them.  For example, having a minimum motor assist speed of 2 MPH is better for them than having it at 3 MPH.

We checked with one of our sprocket suppliers who carries the 7 tooth sprocket with 6mm bore and found it is for a certain brand of 12V and 24V 100W electric scooter motors which run at 3500 RPM. They sent us a photo of the motor's shaft with the sprocket removed which is posted below.

We do not know if a machine shop would be able to machine and thread an E100 motor's shaft to accept the 7 tooth sprocket though.

Unfortunately, just replacing the motor to this one and using a 7 tooth sprocket instead of a 9 tooth wont help the Razor E100 scooter much or at all because of the higher RPMs of this motor.  I wonder if the shaft could be replaced such that this shaft pictured could be put on a slower spinning motor such as the stock E100 motor which I assume spins at around 2500 RPMs.  The idea is to lower the load, the top speed, and the "pushoff" speed of the scooter without having to spend a lot of money on it.  It is a shame that the E-100 doesn't come stock with the smaller shaft that accepts this 7 tooth sprocket.  That would be nice since the stock 47 tooth rear sprocket is already large compared to the size of the tiny rear wheel.  Again, this is for small kids that are just learning to balance a bike so there may be training wheels on the scooter.  The lower speed would be very beneficial to them while learning.

  The only other idea I can think of is to use an 8 tooth sprocket (which I already have) with the same bore as the E-100 motor shaft, and somehow use 1 or 2 set screws to prevent the sprocket from slipping on the motor shaft.

I just checked my 8 tooth sprocket and it appears it has about 1/4 inch (6.35mm) bore so I am wondering if it could be widened to the size of the E100 shaft and held in place with 1 or 2 set screws on the flat part of the motor shaft.  It is only a 100 watt motor so there is not much torque.  Dropping 1 tooth on the front sprocket is equivalent to adding 6 or 7 to the rear, but with better turning clearance. 8-55 sprockets on the E-100 would drop the top speed from 10 MPH (9-47 stock sprockets), to about 7.5 MPH.  It would also likely feel "snappier" and work better on packed dirt.  This is worth trying in my opinion.  I will have to get another E100 and make this work.  Anyone have advice for me?  Pitfalls to watch out for?  Should I use 1 or 2 set screws?  Will it hold?  Since there is only one flat spot on the motor shaft, can I put 2 set screws there side by side on the sprocket?  Notice from the attached pic that the sprocket is not just "flat".  There is plenty of depth to it to allow room for set screw(s).  That entire depth though would have to be bored to the right diameter to allow it to slide onto the E-100 motor shaft.

  Also, to make the D bore, could the sprocket be bored to a round hole and then material added back in to make the D shape bore such as welding a straight chord (geometric definition) across a portion of the round bore?

A sprocket secured with a set screw will work well with a 100 Watt motor. One set screw in the flat area of the shaft should do the job, although two would be better if that is an option. 

Although probably not necessary with a 100 Watt motor, drilling a small dimple into the shaft where the set screw or set screws will rest will help to secure the sprocket in place. Also using Locktite on the setscrews will prevent them from loosening while the scooter is being driven.

Okay thanks for the reply.  It sounds like this is worth the effort to try to get working, provided the cost of boring the sprocket to the proper hole diameter and getting the set screw to work is not too expensive.  

Also, a good side effect of lowering the top speed of a scooter is it extends the runtime between charges and increases the mileage between charges too.

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