Quick and simple fat bike bbs02 solution

e-waka

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Dec 22, 2014
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Maungakaramea
Whipped up this bike for the whanu to ride over the xmas break, I couldn't find too many cheap practical solutions on here for the great bafang mid drive for a bike with the 100mm bb - so here is one idea that sorted it for me
After a bit of a measure up I cut about 10mm of on the sprocket side with the angle grinder.
IMG_20141220_160845_407_zpsb8c533fd.jpg


And on the other took of near all of it right up to the stay, I think I got roughly 75mm in the end, not enough for the lock nut but plenty of meat for the one, squared it all up by eye with the belt sander checking with a square a few times, hit it with the rotary grinder inside, sweet as,
SDIM5075_zpsd318346f.jpg

sprocket on backwards and seems to work no worries.
Cranks are a bit of an issue, the right hand single speed that came with the bike fitted stock - once i ground out the sprocket.
The LH one i tried bending cold and it worked like a charm, in the vise with pipe on, put the pain on it and no problem, took a few goes to get it right and few more to true it up, seemed to handle it fine.
what I like a bout this bike is it is solid as a rock at speed , esp good at being ridden with no hands, and shes a head turner, i barely got a look at my much better bikes on Christmas day, this is the bike they all want to ride!
SDIM5070_zpsbf537be5.jpg
 
Is that the Mongoose Dolimite bike and a Bafang 750W kit?
Can you explain what you had to do to the cranks to make it work.
How well does the bike perform with Bafang kit?
 
wow!
 
Hwy89 said:
How well does the bike perform with Bafang kit?

Here's a video from Doug Snyder's testing of his modification kit. I'd say the Bafang 750w mid drive works pretty good on a Fat Bike. :)

[youtube]UhYp3AYv154[/youtube]
 
Yeah I saw that video and I want to put one together but don't want to have to pay an extra four hundred bucks for the long axle mod to the Bafang kit. That's why I got excited when I saw that the BB could be cut down enough to accept the stock kit. I was hoping for a clearer explanation. The title says bbs02 so that answers one of my questions.
 
Hwy89, these threads might be of interest to you.

http://endless-sphere.com/forums/viewtopic.php?f=28&t=63250

http://endless-sphere.com/forums/viewtopic.php?f=28&t=62518
 
Thanks cjh. The links you posted helped a lot.
I was thinking about whether the chain line would be offset too far and hadn't considered that the pedals wouldn't have enough clearance to rotate.
I still plan on mating a Bafang BB02 to a Walgoose Dolimite 7 speed but undecided if I should buy the modified kit for the wide bottom bracket or do the quick and dirty hack job on the frame. I would like to hear more from others who have studied this and get their opinions.
 
Hwy89 said:
Is that the Mongoose Dolimite bike and a Bafang 750W kit?
Can you explain what you had to do to the cranks to make it work.
How well does the bike perform with Bafang kit?

Yes and yes,
I simply put the crank in the vise put a 2" pipe over it and bent it, then bent it back to tru it up, took a few goes but its easy enough.
I read on the net dont do it - people seem dark on straightening even slightly bent cranks but i am the type of guy who has to try it anyway and can assure you these old square drive take it with ease. You can see the marks on it, just behind the nut the vise marked it up a bit and the two bright marks are where the pipe bit in, which could be avoided with suitable padding, the scuff marks in the middle are from some thing else.
SDIM5094_zps7db9eb88.jpg

The bike really performs well, i am getting 48km hr top, (stock to 14) and enough low down to be pretty good on tight techy type single tracks. Lack of suspension is bit rough but I have to say I like it very much. It needs a careful rider as this much power is a little much for the cheap cluster and freewheel. To begin with i had chain line issues in top gear, i solved that by dishing the sprocket more, I put it in the vise with spacers and squeezed way more dish into it, trued it by bending with adjustable spanner,
SDIM5097_zpsa9221aa6.jpg

sweet as perfect now!
SDIM5102_zps5f56436b.jpg
 
Thanks for the clarification e-waka .
I'm leaning more towards doing it your way. Was there any other machining needed on the BB other than squaring and de-buring the cut ends? Do you still feel that the single lock nut will hold?
I will be spending the summer camp-hosting at a remote campground. Access is via a Forest Service road with lots of washboard. My hub motor bikes would have no problem with the hills except that I have to keep the speed up which gets me bouncing so badly on the washboard that I can't keep control. I need a set up with enough low end torque to crawl up the hills. Hence the desire to build a mid drive.
I could probably covert a full suspension bike but for some reason I have wanted a fat bike since I saw my first one.
 
Hwy89 said:
Thanks for the clarification e-waka .
I'm leaning more towards doing it your way. Was there any other machining needed on the BB other than squaring and de-buring the cut ends? Do you still feel that the single lock nut will hold?
I will be spending the summer camp-hosting at a remote campground. Access is via a Forest Service road with lots of washboard. My hub motor bikes would have no problem with the hills except that I have to keep the speed up which gets me bouncing so badly on the washboard that I can't keep control. I need a set up with enough low end torque to crawl up the hills. Hence the desire to build a mid drive.
I could probably covert a full suspension bike but for some reason I have wanted a fat bike since I saw my first one.

Very simple straight forward on the bb, i will say its some stern stuff, not just mild steel, bit hard to hand file.
The single lock nut comes loose, I have a good tool to tighten and didn't bother with loktite just yet because I want to paint it soon and its really no problem at all to keep an eye on but later on if i have on going issues i will loktite it.
Fat bikes are cool and In certain going superb but you can forget any idea the tires are going to be a substitute for full suspension, air is undamped and bouncy, letting the tires down is all very well but she plows ahead and wont corner if you do, a hard tail is one thing but front too, nah a major step back on washboard back roads or anything much off road imo, Add to that this is a cheap bike, every part will let you down soon, eg all bearings come dry and unsealed, axles are soft and brakes are appalling. Its a road bike and a cruiser for town type bike.
 
I'm not entirely sure I'd describe this hack as, "quick and simple". Perhaps, "cheap and cheerful" fits better? ;)

I have the California e-bike 100mm BB conversion of the Bafang 750w mid drive and that was a lot quicker and simpler to install - much more expensive of course.

Oh, but FWIW, I've used a chainring adapter to keep my 36t chainring and my chain line is awful to the 2 lowest gears, so I effectively have 7. I guess spending money doesn't always solve every problem. ;)
 
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