Front Direct Drive Hub Doesn't Fit

OldTimer

100 mW
Joined
Jul 26, 2015
Messages
46
Location
Hernando, Florida USA
I received my ebike conversion kit yesterday and tried to install the front wheel. My front fork drop-out is way too small.
REVISED: Purchased a caliper and measured the slot for the front axle and it is 8mm. OUCH!
DSCF7046 x2.jpg
It takes a 13mm (or 1/2" for a better fit) wrench. I started filing the drop-out to see if I could make it fit but quickly realized that is was going to take a lot of filing and would probably weaken the drop out. I took the wheel and installed it on my wife's bike just fine. My bike's rear wheel takes a 15mm wrench so I'm thinking I need to order a rear wheel direct drive motor.
DSCF7045 x2.jpg
What should I do to make sure it will fit before ordering?
Thanks
 
Post a link to the kit you bought and also a link, or make model of the bike you want to convert.
 
Do not depend on the wrench size to determine the diameter of a fastener. Manufacturers are notorious for ignoring standards.
Use a ruler to measure the widths or get a cheap set of digital calipers from Ebay ($12-20 depending on quality).

Per WikiPedia:
"Diameters for front thru axles include 20 mm, 15 mm (most common), and 9 mm. Rear axles typically have diameters of 10 or 12 mm."
https://en.wikipedia.org/wiki/Bicycle_wheel

A typical vintage front dropout should accept a 10mm diameter axle but those that use skewers may be a bit narrower ...
(my Miyata forks measure just over 9mm stock).
The axles sizes that I have seen on hub motors are 12mm or 14mm in diameter but the ends normally have 10mm flats machined on them.
A notable exception is the Bafang SWXU hub I just recieved. It is turned down and threaded to 10mm in diameter on both ends.

The size of the axle is also very important to determine the proper size of the torque arm(s) required.
Front_Fork_Axel.jpg
 

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wesnewell said:
Post a link to the kit you bought and also a link, or make model of the bike you want to convert.

Here is a link to the kit:
http://www.ebay.com/itm/48V1000W-26-Front-Wheel-Electric-Bicycle-LCD-Display-Motor-E-Bike-Conversion-/371159330505?hash=item566ad1eec9

The Bike is a Huffy Snake River from the early 1990's (REVISED: 1980's made in USA)
DSCF7050 x3.jpg
 
Putting 1000 watts hub on a front fork is asking for trouble but I would bet dollars to donuts that the axle is 10x14mm.
I would also bet that 1000 watts is NOT the nominal continuous rating but the maximum instantaneous draw.
(I am very cynical about ebay vendor's claims when they neglect to include the full specifications).

If I remember correctly you said that it was a steel frame. Get a sharper file --- and go SLOWLY on the filing.
It does not take much to remove 1 mm of steel.
You are also going to have problems with the axle retainers (those little washers that 'clip' into the drop outs).
I tossed them on my Critical Cycles frame but I am NOT recommending that for 'legal' reasons.
 
I don't know anything about that bike, but it looks more like a road bike. Still, there shouldn't be a problem mounting that motor on it assuming the dropouts are standard 10mm. if the dropouts aren't wide enough, just spread the fork out until it is. I'm assuming the forks are steel. And that is a 1000W motor. More than I'd put on a front fork, but it should work. It should come with a 26A controller that has a max limit of 63V. What doesn't fit? To be sure, you'd be better off with a rear motor on that bike.
 
No offense meant stating the obvious, but the flat side of the axle slides into the fork, and the round side takes a huge nut compared to your original wheel. The flat side should be 10mm.

The huffy could possibly have a 9mm axle diameter, and a very tight dropout. I wouldn't fear much, filing it out 1mm to 10mm.

I wouldn't file the motor axle any smaller, just open up your dropout, and get a torque arm for it.
 
Actually get 2 torque arms, one for each side of a front axle. Think about what would happen if the dropouts broke.
otherDoc
 
LewTwo said:
Do not depend on the wrench size to determine the diameter of a fastener. Manufacturers are notorious for ignoring standards.
Use a ruler to measure the widths or get a cheap set of digital calipers from Ebay ($12-20 depending on quality).

Thanks for all of the great advice. I purchased a cheap digital caliper at Harbor Freight and measured my front drop-out axle slot and it is 8mm wide and 17mm deep. I did some filing on it but stopped when I got to 9mm wide. I need to file about another 1.2mm for the ebike wheel to fit which may ruin the fork for converting back to the regular bike wheel. The axle on the ebike front wheel kit is 14x10mm.
DSCF7085 x2.jpg
I measured the rear drop-out axle slot and it is already 10mm wide. Definitely should have ordered a rear wheel kit in the first place.

In the mean time, I went ahead and mounted the ebike front wheel on my wife's Kalana Sunfish 7spd Cruiser bike which also has a steel frame. Her bike's front drop-out axle slot was already 10mm so the wheel fit just fine. I installed a torque arm but I'm not sure I installed it correctly. Please take a look and let me know.
DSCF7069 x2.jpg
 
The point of the torque arm(s) is to keep the axle from rocking clockwise/counterclockwise.
Put a wrench across the flats and see if you can rock it.
If not then you should be good.
 
LewTwo said:
The point of the torque arm(s) is to keep the axle from rocking clockwise/counterclockwise.
Put a wrench across the flats and see if you can rock it.
If not then you should be good.

Thanks, I was afraid that I had put in on backwards since most of the front torque arm online photos show the torque arm mounted behind the fork instead of in front of the fork like I did mine. Did you see my note about the tabbed washer in the photo?
 
OldTimer said:
Did you see my note about the tabbed washer in the photo?
I did but I am not sure where those originated. Insufficient data --- does not compute.
They could be 'retaining washers' that I referred to in an earlier post, or washers used to fill the area inside the 'lawyer-lips' or they could be anti-rotation washers provided by the hub-motor manufacturer. If they are the latter then that function is fulfilled by the torque arms.

Did you use one or two torque arms?

Another piece of advice:
Use a bit of blue loctite on the axle nuts and the fasteners for the torque arm(s).
If 'you' have a problem on 'your' bicycle you can kick yourself but if your wife has a problem on her bicycle .... a little extra insurance/care might be warranted.
 
OldTimer said:
Thanks, I was afraid that I had put in on backwards since most of the front torque arm online photos show the torque arm mounted behind the fork instead of in front of the fork like I did mine.
Yes - you did put it on backwards.
Here's why:


The axle torque is in the opposite direction of wheel rotation. When the TA is in front of the fork, the torque tends to throw the axle out of the dropout. With the TA behind the fork, the TA forces the axle to seat deeper into the dropout. Sort of imagine a big wrench on the axle flats and you are giving it a mighty twist....

Don't worry about the tabbed washers - they are the poor man's TA. These are standard fare but your TA will do the job much better.

If your fork had lawyer's lips (little bumps at the tips of the dropout), then you should have installed 'C' washers on the axle before installing the regular washer and nut. These sit down behind the lips, help hold the axle in place, and make the washer sit flat. 'C' washers are available from most kit suppliers - including ebikes.ca and ebikekit.
 
LewTwo said:
...they could be anti-rotation washers provided by the hub-motor manufacturer. If they are the latter then that function is fulfilled by the torque arms.

Did you use one or two torque arms?

Another piece of advice:
Use a bit of blue loctite on the axle nuts and the fasteners for the torque arm(s).
If 'you' have a problem on 'your' bicycle you can kick yourself but if your wife has a problem on her bicycle .... a little extra insurance/care might be warranted.

The tabbed washers came with the hub motor.
I only used one torque arm because installing a torque arm on the other (right) side of the wheel would require me to cut and re-splice the motor wires. I would rather have two torque arms because you are so right about the grief my wife will give me if she has problems with her bike. Any suggestions for installing a second torque arm? Thanks for tip on using blue Loctite.
 
Might not have to cut and re-splice to get the torque arm or nut on as often (not always) the connectors come out of the plug by bending a little tab on the terminal flat and then pulling the wire free of the plug. The tabs can be bent back out and wires put back in the plug assembly once they are threaded through the arm and nut if need be. But anyway you decide to do it make sure you check the axle nuts often to see that they are secure. The quality of the nuts and the angle of the threads through the nut varies greatly and can cause things to come loose as the nuts don't always lay flat against the washers or frame. Keep an eye on things as it's a front motor and serious things happen when when the front wheel locks up.
 
teklektik said:
Yes - you did put it on backwards.
Here's why:
The axle torque is in the opposite direction of wheel rotation. When the TA is in front of the fork, the torque tends to throw the axle out of the dropout. With the TA behind the fork, the TA forces the axle to seat deeper into the dropout. Sort of imagine a big wrench on the axle flats and you are giving it a mighty twist....

If your fork had lawyer's lips (little bumps at the tips of the dropout), then you should have installed 'C' washers on the axle before installing the regular washer and nut. These sit down behind the lips, help hold the axle in place, and make the washer sit flat. 'C' washers are available from most kit suppliers - including ebikes.ca and ebikekit.

I'm probably wrong but here's my logic in mounting the TA in front of the fork. Based on the axle torque running clockwise, if it moves it will be pushing the TA into the fork and not stressing the hose clamp. If I install the TA behind the fork, it will be pulling the TA away from the fork and placing stress on the hose clamp (the weakest link).

You can't see it in the photo but I installed the 'C' washers that came with the TA on both sides of the axle. I would like to install a second TA if it can be done without having to cut and splice the motor wires. Thanks for your help.
 
There is more than one issue with torque arms, especially if Regen is involved.

Mounting the TA toward the front does reduce stress on the clamp, but it guarantees the torque reaction will attempt to eject the axle from the dropout if the two TA components act independently, which happens if the cross bolt and axle nuts are ever loose (and they tend to loosen over time). If everything stays tight all the time it is probably fine.

Ideally a custom torque arm would be one piece and avoid that issue, as well the arm would not mount to a clamp but instead bolt to something solid.

This is not a many-KW system so it can likely get by without ideal components and mounting.
 
I've got an old Ross Europa with nearly identical fork and IMO really wasn't a good choice for a front motor so I went with Q128H in the rear. Have a look in my sig for a pic or two.
 
Amazing, I'd have expected an 8mm front axle on a much older bike, but not one from the 90's.

Just goes to show, bike stuff gets weird sometimes.

Do flip the Torque arm. But one is plenty, unless your forks are aluminum. As for the clamp, either direction a weak clamp will break. The more likely thing is it gets loose and lets the arm slip down the fork (or up depending on the side), rather than just breaking loose.

A new fork for the Huffy is one possibility, but likely you can replace the entire bike with one of similar quality for $100 or less. Take your calipers, and get one with a 10mm fork.

Or, do like we do, and buy another motor. That type kit is pretty cheap, so go for a rear next time.

One thing sort of touched on. the washers or TA tend to be oversized. So if you have a depression on a fork that would be empty with a large washer on top of it, you must fill that gap. The thing you need to do that is called a C washer. They can be bought at Grin Technology. Or you can look at the picture, and make a home made one that does the same thing by grinding down a tabbed washer.
 
In an ideal world one would have a specifically designed e-bike for each type of terrain, the e-bike would be powered by dilithium crystals and weather would never be an issue. For better or worse it is not a perfect world so one must adjust their expectations to reality. A standard bicycle frame/fork is not designed to resist a twisting force of motor hub axle. There are three issues:

1) The force tends to spread the sides of the drop-out apart which in the worse case can allow the axle to spin inside the dropout.
2) The repeated application of these forces can lead to catastrophic fatigue fractures of the drop out. Think of repeatedly bending a wire coat hanger until it breaks. The type of material and method of forming the drop-out may mitigate this risk as is the case of forged steel drop-outs. Aluminum, magnesium, castings and pressed steel tubes all have the opposite effect.
3) The axle nuts may become loose if the rider neglects to properly maintain the bicycle. In the worst case scenario this may lead to the entire wheel assembly separating from the bicycle. This is also the risk for standard bicycles that was the lead to the creation of 'lawyers lips' and axle retaining clips.

Without some sort of adaptation the reaction is transmitted to the frame via the friction connections of the axle nuts. Some frames/forks provide have adequate material and strength to resist this twisting force in some applications. However in other applications there is a need of something to address the issues. The oldest and most common example is that of the old fashioned coaster brake and it's reaction arm attached to the left rear chain stay.

The next common example to come along was the internally geared rear hub. If memory serves (and please bare in mind that was over half a century ago) the original SA 3-speed hubs used a single anti-rotation washer with a bent tab that inserted in the slot for the rear axle. That is similar to the anti-rotation washers shipped with hub motors.

The base line adaptation of hub-motors are the the flats commonly found on the end(s) of the axles. The moment arm is a bit less than one-half the diameter of the axle. In the best case scenario (smallest diameter axle) anti-rotation washers may double the length of the moment arm (from ~6mm to ~ 12mm). My first e-bike (circa 2005) used this approach. Those washers and properly tightened axle nuts proved to be adequate to the task.

The torque arms have the advantage of fitting tightly around the axle and thus overcome the tendency to spread the sides apart or allow the wheel assembly to separate from the bicycle. They are generally made of steel (or stainless steel) and and are of adequate size to mitigate the problem of fatigue stress. However the main purpose of the torque arm is to increase the moment arm used to resist the rotation of the axle about its center-line. In this case the length of the moment arm is from the center-line of the axle to the point where the arm transmits the force to the fork. As long as the torque arm has adequate strength to transmit that force it matters not what the path that force takes nor what the orientation of the arm is. This is also true for the case of two (or more) piece arms so long as the fasteners joining the pieces together are tight and provide an adequate friction connection to transmit the force without deflecting, bending or otherwise failing. If those fasteners are allowed to become loose then there is a pivot-pin connection and the force vectors become much more complicated. I can think of several cases where a pivot-pin connection is a mute point (i.e the pivot pin is on the center-line of the fork). I will concede that there does exist the possibility of a pivot-pin connection configuration that could lead to a reaction that would tend to move the axle up or down in the drop-out slot (actually I am just too lazy to go through the force vectors for the various scenarios).

Having said all that:
Let turn to the weak point --- the connection of the torque arm to the fork. It would be much better to attach the torque arm to the fork via an eyelet or braze on. In most cases this will is not practical. The next best option is a 'P' clamp. Radiator clamps are used because they are cheap and will fit around nearly any fork. They work but almost anything (short of a zip tie) is preferable to a radiator clamp.

My points in this overly long rant are:
0) The best case scenario is a properly fitted single piece torque arm (and is the least likely as well).
1) There are cases where it is impossible or impractical to mount the a torque arm 'behind' the fork. This can be because of a conflict between the cabling and torque arm. It may also be due to conflicts in the design of the torque arm and the design of the fork.
2) For a hub motor ANY torque arm configuration is orders of magnitude better than no torque arm
3) Two torque arms are better than one but probably only needed in worst case scenarios.
4) As long as the connection, materials and design are of adequate strength and properly maintained the orientation of a torque arm is of no significant consequence.

P.S.
I have been known to replace the fasteners in two piece torque arms with a higher grade, larger diameter ones.
 
dogman dan said:
A new fork for the Huffy is one possibility, but likely you can replace the entire bike with one of similar quality for $100 or less. Take your calipers, and get one with a 10mm fork.
A very good point. Having looked more closely at the picture of the front drop out one may notice that these are simply the sides of the fork tube pressed together with a slot cut in them. Probably the cheapest (worst) possible method of manufacturing a fork drop-out. The rear drop-outs look to be spot-welded steel plates (non too-thick) as well. I think I might start to question the quality of the steel at this point.
 
Get a decent Specialized, Giant, or Trek, post 2000, for no more than $100 used. Or something with a fork you can swap for $20.

Except for the dilithium, I live in that perfect world. At the moment I have a large cargo bike, medium cargo bike, a recumbent, and two full suspension dirt only e bikes running.

Right tool for the job is what I've preached for years.
 
dogman dan said:
Amazing, I'd have expected an 8mm front axle on a much older bike, but not one from the 90's.
I was wrong on the bike's age. It was purchased in June of 1985 from Service Merchandise for about $200. Believe it or not, I still have the original owner's manual.
 
The best advise is get an old colmoly frame specialized, giant, treck used for well under 100usd. The best way of judging a bike is the rear derailleur. Plus look at the handle bars for brake shifter setup for the kits throttle and brake levers. A rear kit is also a better, many reasons.
Now what battery ? It's nice with a the new batteries to fit in the triangle. Em3ev, luna cycle ect. Depends on range.
 
dogman dan said:
Get a decent Specialized, Giant, or Trek, post 2000, for no more than $100 used. Or something with a fork you can swap for $20.

Except for the dilithium, I live in that perfect world. At the moment I have a large cargo bike, medium cargo bike, a recumbent, and two full suspension dirt only e bikes running.

Right tool for the job is what I've preached for years.

I live in a rural area and have a limited choice of used bikes. I did find the following used bike for sale on Craigslist. Would it make a good ebike build?
http://www.bicyclebluebook.com/searchlistingdetail.aspx?id=30950

We have a couple of Walmarts fairly close by so would a bike like this one make a good ebike build?
http://www.walmart.com/ip/26-Schwinn-Sidewinder-Men-s-Mountain-Bike-Matte-Black-Green/26999374
Amazon has more specs on this bike: http://www.amazon.com/Schwinn-Sidewinder-Mountain-Matte-Black/dp/B00FRR8AVW/ref=cm_cr_pr_product_top?ie=UTF8

I used my new caliper to measure the rear drop-out on the black Huffy. The axle slots are 10mm wide and at least 17mm deep. The drop-out is 127mm wide. Will I have any problems installing a rear wheel direct drive kit? The front wheel kit is going on my wife's Kulana Sunfish 7spd Cruiser bike - shown in the TA photo.
Here's a close-up photo of the Huffy's rear drop-out. Looks like that bolt to the left of the axle bolt that holds the derailer on is going to be a problem. I assume the rear wheel kit will have those large 14mm axle nuts?
DSCF7051 x2.jpg
 
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