Broken Axle Stem

[barboma]

So I think the kit I have from Electric Bike Outfitters has a design problem, its a rear wheel geared 350W kit. Either that or the axle failed prematurely on a 10 month old motor and a few thousand miles. The broken axle stem is on the drive side. I have two torque mechanisms (one is an axle nut type and the other is an arm), so its probably not a torque issue and the axles never spun out and I never noticed anything. Its nearly all paved trail riding, which can be a bit rough at times, but its not like I am doing jumps or downhill stuff. I only noticed this as I had the wheel off to get it trued.

Since I have been riding on this broken axle likely for a few months or perhaps longer and never noticed a problem my question is this, is it that serious of an issue? I know its not ideal but I cant afford to go buy another motor from the company right now. Could I shore up the non-drive side with the torque arm and get a few thousand more miles from it realistically? The only long term ramifications this newbie can thing of it that more lateral stress is placed on the bearing which might cause it to fail.

 

[amberwolf]

If the other side does fail, you then have nothing keeping the wheel in the frame, (depending on which part the torque arm/etc end up attached to), and nothing keeping the axle from spinning out. So while the probability might not be high, the resulting damage certainly could be (especially if it causes you to crash and be injured).


I've had axle failures on very securely clamped axles...because it turned out the *other* end was *not* secure, so it rocked back and forth just a teensy bit, twisting the secured end right at the clamping point, and eventually breaking it. This could have happened to yours.

It's usually the twisting from the motor torque that does this, rather than the bumps/etc, but if it allows even a tiny bit of motion at one end, and not the other, in any direction (up, down, twisting, etc), then this kind of failure can happen.

It could also just ahve had a defect in the casting of the axle, or the machining--any sharp cuts or transitions in the axle diameter are stress risers and create places where failures can occur.

 

[barboma]

So while the probability might not be high, the resulting damage certainly could be (especially if it causes you to crash and be injured).

I hear you amberwolf. I looked at the geared side axle and its pretty beefy, as in secure looking. I can always run torque arms and washers on both sides. I think for now I will keep a real close eye on it, checking the other axle every month to any signs of impending failure. Then when I can, I will either switch to a mid drive or order a new motor.

I see alot of 350W greared motors on Aliexpress for about 100 bucks (which is a 1/3rd of Electric Bike Outfitters sells them for). How would one know if it will work with EBO's housing? While I have switched Rims before, I would have no clue how to lace a new motor in.

 

[amberwolf]

I can always run torque arms and washers on both sides.

WIth a broken axle, those won't do you any good on the broken side, unless you are going to weld the axle back together first.

I think for now I will keep a real close eye on it, checking the other axle every month to any signs of impending failure.

You probably will not be able to see the crack in the axle until it breaks completely, unless you are removing it from the bike and examining it's entire length with at least a very good magnifying glass and extremely good lighting. Probably not even then, unless it rusts at the crack and nowhere else, or something similar.

I see alot of 350W greared motors on Aliexpress for about 100 bucks (which is a 1/3rd of Electric Bike Outfitters sells them for). How would one know if it will work with EBO's housing?

You won't, unless you can get measurements of all the stuff that interfaces between housing and motor on each--the ring gear to planet gear size/diameter, and number of teeth / size of teeth, the width of teh motor / shell inside, the axle diameter on each end / bearing inner diameter, etc.

It's possible they'd fit...but I couldn't even give you a probability percentage. Sometimes cores from the same manufacturer, on the same motor type, but different versions (which may or may not be marked as such) wont' fit in cases of each other.

DD hubmotors...there's a lot less stuff to match, and more of them are exact clones of each other in the generic "500w" to "1000w" range, so pretty good chances on those, for a number of reasons.

Geared hubmotors...dunno. Too many things can be different, to guess.

If EBO would tell you which brand they use, you'd have a better chance...but they have no reason to do that.

While I have switched Rims before, I would have no clue how to lace a new motor in.

Exactly the same as switching rims, but the other end of the spoke...so you ahve to take each spoke out of the rim *and* motor, one at a atime, and install them into the new one. But that only wokrs if the spoke flanges on the new motor are the same width *and* diameter, otherwise you need new spokes. (my guess is new spokes would be better anyway, as the existing ones are probably 12g, which are too thick to tension right for most bike rims, and so they get loose and can break--or if tensioned enough they can break the rim...getting new 14/15g butted, or 13/14g butted if you have to, would make a stronger wheel)

 

[barboma]

DD hubmotors...there's a lot less stuff to match, and more of them are exact clones of each other in the generic "500w" to "1000w" range, so pretty good chances on those, for a number of reasons.

Gotcha on everything else. Question: what would you (or anyone else) recommend in terms of durability and cost for a motor? DD, Mid-drive, Geared? I have not had a whole lot of luck with the kit from Electric Bike Outfitters -- granted some mistakes have been my fault and thats why they have been able to dodge warranting it, but I love the whole electric bike thing and dont want to give up on it buts its been an expensive hobby.

 

[barboma]

Also, do you think it would be worth it to take the motor to a machine shop and see if they can weld the stem on, as a temporary measure? Might be cheaper in the short run. One problem I see is the wiring as I cant see they can do that with the wiring melting.

 

[docw009]

I've got two of these 36V 500W geared motors running in my ebikes, and a third one sitting as a spare. Less tha $179 shipped for a complete motor/wheel/electronics.

https://www.ebay.com/itm/ebikeling-36V-500W-700C-Geared-Front-Rear-Electric-Bicycle-Conversion-Kit/273861102461?hash=item3fc364cb7d:m:msfpgwVOHWFnKadDWgqiuxg:sc:FedExHomeDelivery!60565!US!-1

Weak point on the LED kit is only 3 level PAS, but it is a 22A controller, so offers good power. You could also just splice the motor into your existing wiring and use your current controller

 

[John in CR]

Depending where the break is and can mod the bike dropout, you can repair it by making a steel sleeve that is treaded on the inside and just screw it on over the crack and support the axle. It won't offer any anti-spin protection, but on those small motors you can't really rely on the hollow side axle for your torque arms anyway.