Single speed freewheel doesn't fit bafang geared hub motor

[jpm600]

Hi,

This is my first post, but i've done plenty of very informative reading through the many posts of the many experts that make this forum such a great place.

Anyway, i'm putting together a fairly lightweight electric assist road bike with a rear bafang geared hub motor, small 6 FET controller, 10s LiPo batteries.

I've got everything sorted except a freewheel won't fit on my hub motor. I bought a bafang swxp-r from elifebike. this one http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2012-8A-RK1S.8TKFU

anyway, i've tried 2 standard freewheels and they both start fine but bind after 3-4 turns. i didn't want to force it, so i pulled it off and measured. I measured 34.7mm to the top of the threads and the threads are metric 1.0 NOT 24TPI.

Is this a size that exists for scooters or something or is it just china quality control(or lack thereof) cutting the wrong thread pitch.

Anyone seen similar.

 

[d8veh]

Bafang motors have the standard free-wheel thread that you should be able to fit any standard free-wheel to. Are you sure that you're not cross-threading, which is very easy to do?

 

[jpm600]

Yeah,

It should have a standard freewheel thread and the motor diagram on the website says it is. (ie. 1.375" x 24TPI)

But when i put a 24TPI thread gauge accross it, it doesn't mesh. Metric 1.0 does mesh.

But yeah, i checked very carefully that it's not crossthreading, it's not. It spins on beautifully for 3-4 turns then stops really tight.

Oh well, Not sure whether to try to jam the standard free wheel on, or try to get an old french tread free wheel, which it seems to be.

thanks for the suggestion

 

[anpate]

The following is from Sheldon Brown's very informative page about freewheels: http://sheldonbrown.com/freewheels.html

"All recent freewheels and threaded hubs, regardless of where made, use ISO threading. The older British and Italian standards use the same thread pitch but a very slightly different thread diameter, and are generally interchangeable. However, for strong riders and on tandems, it is best not to mix and match -- freewheels sometimes do strip the threads of aluminium hubs. A French freewheel may start to thread onto an ISO/British/Italian hub but will soon bind. An ISO/British/Italian freewheel will skim the top of the threads of a French hub and will slip forward if an attempt is made to use it. Do not force a freewheel -- you will ruin the hub."

I was looking at this one for my Mac because it' states in the ad that it is an English thread and from what I've read that's what fits the Mac motors.
http://www.ebay.com/itm/Shimano-16-tooth-freewheel-for-1-2X1-8-/360831309351

 

[jpm600]

Yeah, English thread is standard ISO thread which is 1-3/8" diameter and 24TPI (threads per inch). Every other hub motor i've seen or heard of has that standard thread, just not this one.

For you mac motor that freewheel should be fine, but, so should just about any, as long as it's not M30 x 1.0 which are the smaller BMX freewheels.

Seems like mine is just an oddball stuff-up.

I might try to butcher it to make it work. Or try to find another side cover from a bafang motor that will fit.

 

[jpm600]

Well, i've finally got a gear on my bafang swxp-r (bought from elifebike). I had to file the thread with a thread file to open up the thread for the first 6 threads(ie butchered it on).

My build is actually an old cr-mo steel road bike converted to single speed fitted onto this little rear hub motor, 6 FET controller, and 12s 5ah hobbyking lipo's. Ready to ride with batteries and everything it's right on 15kg.

it runs at ~32km/h on the flat with no peddling. top assisted speed with hard peddling on the flat is ~45km/h. It comfortably helps me up hills at 20-25km/h(gearing is 42/16 and i wouldn't make it up those hills without the motor.

I made my 50km round trip to work with plenty of peddling at ~28km/h average on a single charge.

In short the swxp motor is a great little lightweight motor, but I cant recommend the rear drive one as the freewheel thread was definately wrong.