How To Build An Ebike From Scratch: Tinkering

We crawl one step further: confirm as best we can that motor will fit, then buy and test-install it so we can take more measurements.

Step 1: Planning
Step 2: Hunting
Step 3: Tinkering (You Are Here)
Step 4: Buying
Step 5: Assembling
Build Day 1
Build Day 2
Build Day 3
Step 6: Perfecting
Tools List

In our last installment, we bought our frame after doing our research. Its here now.

We Got The Cart. Time For The Horse!

Back in the Planning stage, I decided that, given a choice between a geared hub motor, a direct drive hub or a mid drive, I wanted to use a mid drive. A mid results in the least weight added to the bike, and gives it the most versatility over varied terrain.

Now that the frame is here, its time to take some measurements to make sure my plans were realistic before I go and buy the motor (lets pretend I didn’t already have it, as most folks will not have extra new motors laying around to pick up and use).

If I did not have the motor handy already, I would have measured two things.

Part 1 of 2

First, I would have looked at the length of the axle housing versus the width of the bottom bracket. I want to find out if my motor axle, designed to fit thru a range of 68-83mm bottom brackets, will actually come out the other side with plenty of available threads to complete a proper assembly (a locking plate and threading on a couple of lock rings). Chances are pretty good you can infer this number by knowing your bottom bracket width and buying the correct motor sized for it. Axle length is part 1 of 2 and its the easy part as, effectively, you can just read the motor specs to get this number.

Part 2 of 2

If I had a fat bike, I would next be looking at the frame’s chainstays (which I hope you were at least eyeballing for suitability while you were hunting for the frame in the first place) to see if I needed to upsize the motor. Oftentimes (particularly with 197mm rear dropout spacing) if you have a 100mm bottom bracket, you need to upsize to a 120mm motor to clear a fat bike’s chainstays, which I’ll talk more about below.

This is what you want to see once the motor arrives: Plenty of available threads and they don’t bottom out to the bare axle.

Next as part of this chainstay fitment process, I would take some circular measurements around the bottom bracket to see if the big round secondary gear housing fits reasonably well in that area. It needs to tuck into the frame at the root of the chainstay (but not touch it!). The secondary housing is about 133 mm (5.25″) in diameter. Go find yourself a juice bottle or coffee can thats about that width to best visualize how well (or how poorly) its going to clear. A 1x frame that is meant to hold a single small chainring is often a good frame candidate for a BBSHD, by the way, as the secondary housing is about the size of a 34-36T chainring.

Worst case: draw a circle on a piece of box cardboard, cut it out and overlay it on your frame’s bottom bracket. Will it fit? Chances are pretty good it will. But if its a fat bike, you may need to use spacers to move the secondary housing out further, and this will have implications for chainline (all of them bad, but not necessarily fatal).

What you see in the pic below is the desired result: The secondary gear reduction housing tucks right into the root of the chainstay and bottom bracket. Fitting it so it comes close to but does not touch the chainstay (look closely… the actual thing we have to not touch is a bolt end where the chainstay is bolted to the frame) does not result in a large gap that will be filled by a potentially large spacer.

There’s a gap in this test fitment at the bottom bracket on the left/drive side that will need a shim. That comes in a later step. We’re just confirming the fit to the frame is good right now.

If my efforts showed me I was going to need a large shim to clear the chainstays, this can mean I’m going to have a chain alignment issue once the motor is on. If its bad, I might abandon the BBSHD and pick a different motor. The two most likely alternatives are a Cyclone (assuming you can find one for sale these days) or a Cyc X1 (Pro or Stealth as you please). The Cyc motors are recommended for beginning to intermediate builders, and the Cyclone is strictly for the advanced, experienced builder who understands some metal fabrication is probably necessary coming into the game.

Here’s a quick visual example of what good chainline is, and isn’t. Image courtesy of Lekkie Ltd. Used with permission

Other mid drive alternatives with this narrow bottom bracket could be a BBS02 (unlikely if a BBSHD doesn’t fit for some reason) or a Tongsheng TSDZ2. The latter is more or less in the class of the BBS02 in terms of power level, provided you get one that is properly uprated for 750w.

So, there are alternatives but the BBSHD is a quick and easy motor to install, if it fits. Its probably the quietest mid-drive on the market. Its also relatively inexpensive, mild-mannered (if its settings are worked over since the factory settings are crap) and has loads of aftermarket support. As such in my book its by far the preferable motor to plug into my project (having seven of them, I also can keep one set of spares that work across the fleet). And luckily, since I had a motor already in hand, I was able to quickly determine it fit just fine.

More on Chain Alignment

Notice something about that chainring diagram above? It includes the chainring on the motor and the rear cassette cluster on the back wheel as part of the measurement process. So, at this stage, with only a frame and a motor you are not going to be able to measure much of anything with precision regarding chainline. You are going to be eyeballing things and estimating.

Still, you want to do your best. Look at the picture below and check out where the chain is lined up over the secondary housing, with that Lekkie chainring it has on. Use that as a reference point. If you can spring for a chainring, and a chain (or find an old one in the garage) that will only help you here.

If you have parts on another bicycle (like a back wheel) you will be well-served to take it off of that bike and stuff it on temporarily to the back of your new frame to help with this process. A long hex wrench can substitute for an axle if all it has to do is hold the wheel roughly in place on a stand for 10 minutes while you drape a chain over the cluster and eyeball it.

There are many alternative chainring configs in a successful BBSHD build. These solutions deliver dramatically different alignment results. Consider this a resource for sussing out your build situation.

Whats the extreme for frame fit? A fat bike. Look at how far to the left the motor had to go to not touch the chainstay (Its close but not touching). That is a custom 17mm steel bushing used for a spacer. The chainring is so far out, even being an offset Lekkie I can’t go all the way in to the biggest cog in the back. A Luna Eclipse has too much offset and will not fit.

How Close Does The Motor Go?

Looking at the pics above, the motor appears to actually touch the chainstay root. It doesn’t. But it does get very close. How close is close enough? A good rule of thumb is the thickness of two business cards (or just fold one in half). So if you are thinking you need a bunch of clearance from the secondary housing to the frame… you don’t.

However, you also absolutely, positively do not want it to touch. Having the secondary housing in direct contact with the frame can eventually cause the chainstay on the drive side to straight up break off at the point of contact.

Look at the pics above. This is the result of a 5mm shim that I had on hand: WAY more clearance than necessary. These pics are shown before it was fully tightened (it did get closer when I put the full 90 ft lbs onto it). The lesson here is this is way more clearance than you need or want. Letting the motor sit this far away from the frame will be the difference between great and awful chain line.

Frame Fitment Overview

Here is an excellent tutorial on BBSHD frame fitment, developed and distributed by High Voltage Kits. It should help you visualize and understand the frame fitment process.

What I saw when I did my test-fit (the pics were taken at the time with this article in mind for the future):

  • I’ve got plenty of threads on the motor axle where it sticks out on the non-drive side to clamp the motor down.
  • The chainstay root hinge is cooperating nicely already in that the big round bolt is on the non-drive side. On the drive side, there’s just a small nub of the bolt sticking out. Good news for snug fitment close to the bike.
  • The big round secondary housing (where the chainring will bolt on) tucks right into the available space within the chainstay root.
  • I’m only going to need a narrow shim on the drive side to hold the secondary housing out a bit so it clears that bolt stub that holds the chainstay to the frame (it turned out that 3.5 mm was the magic number).

A secondary observation: the chainstays have an enlarged area allowing wider tire fitment. I used 2.35’s but I think I could go as high as 2.50, which would have been colossal – probably bigger than any available tire of the era – back in 1999 when this frame was manufactured. Thats the sort of tidbit you can’t easily get from a spec sheet (assuming you could find one on a 23-year-old frame), and further solidifies why you need to wait until you can lay hands on the real thing before you start buying parts to hang off of it.

I Had It Easy

As noted I already had a motor and I knew how it was going to fit, pretty much. I also have built bikes with other motors and I know how those fit as well. What if I was doing this for the first time? How would I get around my lack of direct experience?

Ask Around

The internet is chock-full of places where you can ask for help from people who have done what you are trying to do for the first time. Ask them what they think.

  • Post pictures of the frame
  • Ask what will fit
  • Expect to double-check and confirm every word you are told. After all its the internet and there are plenty of bozos out there who can do a great job of sounding like they know what they are talking about (like me!)

What else do we look around for?

Hopefully you have done some due diligence on your build and have picked up on some common issues associated with your chosen motor install. Here’s another common one that I knew was coming, tried to get around… and failed:


The issue is off-center crankarms. All this talk of the secondary housing fitting on the bike and all… think through whether there are more implications of that thick, saucer-sized whatsit being there. Usually its only crankarm and chainring.

The mounting of the crankarm has been moved away from the bike by roughly two centimeters. Your Quack Factor has been increased by this amount… only on one side. Put pedals on the bike and they are now off-center beneath you by that same amount. Not a good thing.

The solution to this is to use ‘offset’ cranakarms. Your drive side crankarm is straight back, as normal. But the non drive side has a kink in it to move the pedal position outward by roughly the same amount that the BBSHD kicks it out on the other side; compensating for the motor’s presence and its effect on pedal placement. This re-centers the pedals underneath you.

HOWEVER, some ebike configurations let you do without the offset. My Lizzard King build was a bike that had a 68mm bottom bracket. I was able to use normal straight crankarms with it. I hoped to be able to do the same thing with The Apostate since it, too had a 68mm bottom bracket.

So I stood up the frame on my worktable, did a snug fit of the motor and laid the crankarms parallel to one another as you see in the picture below. From there, after confirming the rear triangle was symmetric (some frames are not so you have to measure!) I measured the distance from the inside of the crankarm to the very outside of the chainstay. If my prior experience pans out, the frame’s narrow 68mm bottom bracket, combined with a motor whose axle is made to work with up to an 83mm bottom bracket, will give me enough overhang that I do not need to go to the expense of offset crankarms.

Uh Oh

yeah ‘uh oh’ is right… click on that pic to enlarge and see my results. Actually having the frame and for reals bolting the motor in… my supposedly educated guess turned out to be baloney when it came up against reality. You can see for yourself by reading the numbers on the tape (which are pretty accurate in the picture despite my just laying the tape across the parts). The drive side crankarm is considerably outboard versus the non drive side.

So I had to bite the bullet and buy a set of offset crankarms. Oh well maybe I can use the new ones in the picture (forged Shimanos that ran me about US$50) on some future project.


Oh boy did I ever screw this up. This dovetails directly into the ‘buy first and measure everything’ philosophy except… I didn’t. Or more accurately I did it wrong. Here’s the deal:

The frame came with a Salsa Flip Lock seatpost clamp, which is a very nice piece. As I have mentioned already elsewhere, the frame came with an unexpected bonus in the form of a vintage 350mm Kalloy Uno seatpost, which fit me and the bike perfectly. The post was already installed on the bike and (here’s the first place where I screwed up) I never actually removed the clamp and the seatpost. I just adjusted it in situ as the build went on, and clamped a saddle to it.

I did measure the seat tube just below the collar on general principles, and got a measurement of 36.4mm. OK great if I ever need to buy a seatpost clamp thats the size I need. Simple, right?


So if I had followed my own advice, I would have removed the seatpost clamp and realized the stupid thing necks down to about 35mm! It does so for only a short space that is just underneath the clamp. Then it necks up to 36.4mm.

Do as I say. Not as I do. I figured out a way to shim it but thats the only thing that saved me from having to buy a seatpost clamp twice.

The Lesson To Be Learned Is…

Take nothing for granted. If you aren’t sure, go slow. Try and anticipate where your choices can go wrong in advance of paying for parts you have to replace. And recognize you can never get everything right the first time. Build some fudge into your budget for issues like this.

If, using the crankarms as an example, I had waited to buy those arms (and measured the end of each axle to the bottom bracket), I could have totally avoided buying that original set of arms that are now sitting in an extra-parts box. But I got ahead of myself and it cost me fifty bucks. So learn from that!

Enough tinkering already. Lets move on to

Step 4: Buying

Author: m@Robertson

I'm responsible for the day-to-day operations at my place of business: Leland-West Insurance Brokers, Inc. We do classic and exotic car insurance all across these United States. I'm also an avid auto enthusiast, a born again cyclist (i.e. an ebiker) and participate in medium and long range CMP and NRA sanctioned rifle competitions.

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