Dropouts bent or normal?

[nub340]

I am trying to convert an older Electra Cruiser Step-Thru to electric. I noticed the front dropouts appear to be "opened up" a bit. The bottom measures ~10mm, while the top measures ~13mm. Both sides (L and R) seem identical. Are these like this stock, or did they get bent somehow? See attached image for comparison with motor shaft.

When I place the motor shaft into the slot, there is a lot of play and the shaft can rotate a bit too much for my liking. My other Cruiser has way beefier dropouts and seem to be a different design all together and does not have this issue. Anyhow I will be using 2 torque arms, one on each side.

What would be the prudent course of action to proceed? Should I try to close it a bit (I.e. bend it back), or just leave it be? Do they make some sort of adapter/washer that would help, or will the torque arms be enough? Appreciate the input! Thanks.

 

[E-HP]

What would be the prudent course of action to proceed? Should I try to close it a bit (I.e. bend it back), or just leave it be? Do they make some sort of adapter/washer that would help, or will the torque arms be enough? Appreciate the input! Thanks.

I wouldn't try to bend them back since it will just weaken the metal. I think a tight fitting torque arm would be the best practical solution.
TorqArm_V2 might work with the fender eyelets you have:
https://ebikes.ca/product-info/grin-products/torque-arms.html

 

[Phasedout]

If they're steel, weld, or braze, a washer to fill the "lawyer lips". Cut the axle slot a bit narrow, then fill the wide part of the dropout with weld. File to precise fit. Make certain left and right slots are aligned.

 

[PaPaSteve]

Dropout does appear bent.
Dropouts are often mild steel ... squeezing it back to the correct width wouldn't be a problem.
Based on the way the fender brace is scarred it doesn't look like the axle nut clamped on the inner surface of the dropout properly.
Torque arm is a good idea but also make sure there is a washer the fits the axle tight and drops down into the recess of the dropout.
This will improve the clamping force.
You might need to shape a washer to best fit the axle and dropout.

 

[nub340]

Indeed the forks & dropouts appear to be steel. I tested it with a refrigerator magnet which sticks to the forks & dropouts, but not the frame, which is for sure aluminum.

My plan at the moment is to use one of those little C-washers that come with the torque arm kits and modifying it as necessary to fit as perfectly as possible in the groove/depression of the dropouts so that when I tighten the axle nut it clamps down legit, per @PaPaSteve's suggestion. Well, that in addition to the dual torque arms...

Welding will be a last resort if I can help it since I'm trying not to ruin the paint job. But welding on a washer would def do the trick as well.

Much appreciated! Thank you.

 

[Comrade]

Is that a hole in the middle between the fender bolts? There is so little metal there I don't think that fork would survive even a front brake. :lol:

 

[nub340]

Is that a hole in the middle between the fender bolts? There is so little metal there I don't think that fork would survive even a front brake. :lol:

Ha, no :lol: Just a little flake of paint scratched off, you are seeing the primer, not thru it. :wink:

 

[99t4]

Is that the original fork? That does look like a rather dainty dropout.

What's the motor rated at and what are you powering it with?

 

[E-HP]

Is that the original fork? That does look like a rather dainty dropout.

What's the motor rated at and what are you powering it with?

If the dropouts aren't bent, but the manufacturer allows for them to be 30% out of tolerance, I probably wouldn't trust that manufacturer.

 

[Chalo]

No, those fork tips are bent for sure. I remember that song and dance from my first front hub motors I used without torque arms or non-turn washers.

I can't believe it's almost 20 years later and Chinese hub motor makers are still doing it this super dumb way.

 

[nub340]

Is that the original fork? That does look like a rather dainty dropout.

What's the motor rated at and what are you powering it with?

Yeah, totally original Electra Cruiser Step-Thru circa 2008 or so (belongs to my sister). The dropout is definitely less beefy than my Electra Cruiser. It has an internal 3-speed hub in the rear, which I wanted to leave as-is so she can continue to ride it normally up/down the beach. Adding a front motor just to help her deal with a few gnarly hills on the way to/from the beach.

It's a 1000w motor + 48v, 38A, 1000W XLD Brainpower controller which has 3 power levels (going to keep it on low). Battery is 14s5P (52v). I've melted a couple 500w motors on the same hills before, but this setup handles the hills no problem. Used it on my Electra Cruiser for years so I'm just swapping it over to hers.

 

[nub340]

No, those fork tips are bent for sure. I remember that song and dance from my first front hub motors I used without torque arms or non-turn washers.

I can't believe it's almost 20 years later and Chinese hub motor makers are still doing it this super dumb way.

Do you think I should bend them back a bit, then?
What "super dumb way" do you mean, exactly?

 

[nub340]

Is that a hole in the middle between the fender bolts? There is so little metal there I don't think that fork would survive even a front brake. :lol:

Ha, no :lol: Just a little flake of paint scratched off, you are seeing the primer, not thru it. :wink:

No, you're right! My bad. There is indeed a third hole (sorry had to wait until today to check again, was away). Good eye man. Yeah, I think I'll at least weld that center hole up.

 

[nub340]

If they're steel, weld, or braze, a washer to fill the "lawyer lips". Cut the axle slot a bit narrow, then fill the wide part of the dropout with weld. File to precise fit. Make certain left and right slots are aligned.

If I understand you correctly, you're advising NOT to bend them back, but instead add new metal to the inside of the slots and then file them to the correct width (~10mm)?

 

[Chalo]

Do you think I should bend them back a bit, then?

I would, if I had appropriate tooling available like a machinist vise or parallel jaw pliers. I would not chomp on it with vise grips.

And most importantly, I would not run that bike again without torque arms.

What "super dumb way" do you mean, exactly?

I mean transmitting the motor's reaction torque through flats cut on a threaded axle. It's asking for trouble. For over 120 years now, you can get coaster brake hubs that do better torque retention cheaply and simply. But Chinese motor manufacturers are too committed to half-assery to do it that way.

It's not hard, not expensive, and there's no development necessary. They would just have to use their brains a little bit and do something just a little bit differently. And apparently they can't do that.

 

[nub340]

Do you think I should bend them back a bit, then?

I would, if I had appropriate tooling available like a machinist vise or parallel jaw pliers. I would not chomp on it with vise grips.

And most importantly, I would not run that bike again without torque arms.

What "super dumb way" do you mean, exactly?

I mean transmitting the motor's reaction torque through flats cut on a threaded axle. It's asking for trouble. For over 120 years now, you can get coaster brake hubs that do better torque retention cheaply and simply. But Chinese motor manufacturers are too committed to half-assery to do it that way.

It's not hard, not expensive, and there's no development necessary. They would just have to use their brains a little bit and do something just a little bit differently. And apparently they can't do that.

I see. Thanks for clarifying. Yeah, I agree it seems kinda dumb way to do it.

To be clear, I haven't actually ridden the bike yet, as I'm still putting it together. I just put the wheel on while the bike was upside down and tested that it spun, etc. I did not have the torque arms on yet though, so I will be sure to not do that again. Thanks so much for the great input, I want to be sure it's safe for my sister to ride.

 

[amberwolf]

I just put the wheel on while the bike was upside down and tested that it spun, etc. I did not have the torque arms on yet though, so I will be sure to not do that again.

Unfortunately, with the poor design used (axle flats) for torque transfer in almost every hubmotor ever made, even just spinning up a motor, upside down bike, no load, can apply enough torque to break things, which I learned the hard way some time ago.

 

[nub340]

I just put the wheel on while the bike was upside down and tested that it spun, etc. I did not have the torque arms on yet though, so I will be sure to not do that again.

Unfortunately, with the poor design used (axle flats) for torque transfer in almost every hubmotor ever made, even just spinning up a motor, upside down bike, no load, can apply enough torque to break things, which I learned the hard way some time ago.

Ouch! Duly noted, sir.

 

[RunForTheHills]

Maybe Electra will sell you a replacement fork. The current model Electra Cruiser has a steel frame and the fork looks a little more robust than yours. Although your fork looks like it is made from steel. Aluminum would be thicker.

 

[amberwolf]

2
Maybe Electra will sell you a replacement fork. The current model Electra Cruiser has a steel frame and the fork looks a little more robust than yours. Although your fork looks like it is made from steel. Aluminum would be thicker.

But easier to just snap without warning from axle torque problems, should there be a failure of torque arms, etc.

 

[PaPaSteve]

Cast aluminum can't be bent back and forth repeatably in the same way mild steel can be bent and straightened without worry.
The dropout looks to be silver brazed to the fork leg.
If metal is to be added it should be done with some form of brazing.
Electric welding is much hotter and could boil out the silver brazing causing the original attachment to be weaker.

BTW ... I have many years experience making bicycle frames.

 

[docw009]

Yikes. My steel front fork has a hole too. I've got a 500W bafang motor on it, but with a 20A controller and 48V, it's got to hold 1000W peaks.



I had that mild steel torque plate on one side, and a store-bought torque arm on the other, The bafang cable allows me to torque them down to around 25 ft-lbs with a torque wrench. Marked the nuts like I always do, and they never move,

 

[PaPaSteve]

That's a beefy looking TIG welded fork.
With your custom anti-rotation device fastened to the fender eyelet the extra hole isn't anything to fret over.
Good work !

 

[Comrade]

I had that mild steel torque plate on one side

That is some serious Robinson Crusoe craftsmanship right there. :lol:

I made a similar torque arm, 32mm center to center, and tried doing the math about how much shear torque the small bolt would see. It was much more than I expected.

 

[Chalo]

[I made a similar torque arm, 32mm center to center, and tried doing the math about how much shear torque the small bolt would see. It was much more than I expected.

It's irrelevant compared to the force applied at 5mm radius on the axle flat. If anything fails, it will be the axle flat or the torque arm flat, whichever is softer. You don't have to worry about the mounting bolt.