Help fitting a torque arm to a Bafang 8 Fun motor

[TomBrown]

Has anyone fitted a torque arm to a bafang 8 fun QSWXK 36v 250W motor?

The motors I have come with two torque washers that fit on the very short flat sided parts of the axle on each side of the motor. The rest of the axle is round so there is no way that a torque arm can be fitted on the outside of the forks as shown in d8veh post "how to fit a torque arm". I have had the kits which I purchased from 8fun Bikes for 2 years now with no problems until about 6 weeks ago when the motor spun out of the isync fork on my trek 4300, this occurred shortly after fixing a puncture so it may be a fault of not tightening the wheel nuts enough. I have just replaced the fork with a SR Suntor V brake fork and before I put the motor back on I was thinking of fitting a torque arm and do the same to my Trek 4500 which has an SR Suntour disc brake fork which so far has been ok.

 

[Deleted member 4366]

If the axle is round, you can't do anything except do the nuts up tight.

Make sure that the first washer fits within the dimple on the drop-outs otherwise you can't tighten the nut properly and if you do it too tight, the front of the drop-out will pop off. You can file the washer, use an eccentric one or file the drop-out deeper.

 

[TomBrown]

If the axle is round, you can't do anything except do the nuts up tight.

Make sure that the first washer fits within the dimple on the drop-outs otherwise you can't tighten the nut properly and if you do it too tight, the front of the drop-out will pop off. You can file the washer, use an eccentric one or file the drop-out deeper.

 

[TomBrown]

Thanks d8veh.

The inside torque washers fit well in the drop outs and the outer washers fit inside the dimple ok. I think its getting the balance of making sure it is tight enough to stop the axle spinning but not to tight as to stress the fork or strip the threads.

 

[Alan Quay]

I ran a Q128 (probably slightly more torque than your swx, but not a lot) in my suntour forks for about 1000 miles. I did not have a torque arm, and as per d8veh's recommendation, tightened them as much as I dared.

Since I carry it on the bike and, in the absence of a torque wrench, I went with my 6" adjustable almost as tight as I could go. (I'm a bit of an urangutan though.)

Personally, I never had a problem, and those forks are still in use, albeit with a rear drive motor.

 

[TomBrown]

I ran a Q128 (probably slightly more torque than your swx, but not a lot) in my suntour forks for about 1000 miles. I did not have a torque arm, and as per d8veh's recommendation, tightened them as much as I dared.

Since I carry it on the bike and, in the absence of a torque wrench, I went with my 6" adjustable almost as tight as I could go. (I'm a bit of an urangutan though.)

Personally, I never had a problem, and those forks are still in use, albeit with a rear drive motor.

Thanks Mike

I am probably a bit to cautious about over tightening than perhaps I should be.

My Trek 4500 with SR Suntour XCM forks has done about 6000 miles without a problem. My Trek 4300 had an isync fork and had done about 3000 miles before the spin out, hence why I have replaced it with a SR Suntour fork and that I know the motor will fit without any modifications.

My son was using the bike at the time of the spin out and he likes to use the throttle, so I guess the start up torque on either an under tight motor and/or a weak fork caused the spin out, fortunately he was not hurt. I prefer to use the pedelec and then only to flatten the hills. Hopefully it will not happen again.

I need new batteries before we can use the bikes again for any serious mileage as the two that came with the kits have just about had it. So I am looking to see if I can find a uk supplier of 36v 9Ah, 10Ah or even a 15Ah rack mount or possibly a bottle battery if it will fit in a 16" frame. So far it looks like I could buy a new kit for not much more than a battery in which case I my look at a rear drive option.