Budget "Supermoto" build - DH MTB + BBSHD + Slicks

[kungpho]

Hi y'all, I'm a mountain biker and bike commuter but fairly new to ebikes. With the winter approaching I've been thinking about getting an electric bike to make my commute easier when it's raining and I don't want to pedal, and a few months back a coworker offered to sell me his converted cargo bike (Mongoose Envoy + BBSHD kit) that he was sick of dealing with. $750 seemed like a solid deal so I bought it off of him, thus starting my journey.

Long story short the cargo bike was convenient but sketchy to ride loaded fully and/or at speed. I decided I wanted something with full suspension and a slack head tube angle for more stability and the ability to quickly ride up curbs and dodge cars as is unfortunately sometimes necessary on my commute. So I spent a few months watching FB marketplace for an older DH mountain bike as a new chassis for the motor. Last week I found a perfect donor - a 2013 Turner DHR listed for $400.


pictured here with some slick tires installed. I don't plan on taking this setup on singletrack (much) as I will be sticking to my analog bike.

Originally it looked like the existing UPP 52V pack would just barely not fit with the rear shock piggyback, so I started looking into building a custom battery pack. I just now realized that I can flip the shock and get more space in the triangle! So I will be able to get things rolling with the current pack.



So, I pulled the motor off of the old bike and slotted it on the DH frame. I had to dremel off an ISCG tab to get it on, and the realized I'm a dingus and the BB shell width on a DH bike is 83mm, so the 68mm BBSHD is a bit short. So here's my question to the forum - is it possible to swap the motor housing for a longer (presumably 100mm) housing?

Anyway, there was enough thread sticking out the far side to get the motor tightened up, albeit without the left side support bracket. Good enough to take the bike out on an initial romp.



More to come...

 

[Tyler5883]

Based on the drawing I could find, it looks possible to switch out the housing, but not sure if it would be worth your time, or if you can even source just the motor housing with a longer shaft. Looks like you would need to swap out the part listed as number 1 in this drawing, which is the entire housing. This could also mean you have to swap out part number 5 in this drawing due to that coaxial shaft in the center, depending on how the center shaft interfaces with the motor housing.



You don't show pictures of how much thread is left, but is it possible to make custom nut to allow you to use the parts you have already?

Not sure about your capabilities and access to the tools required, but that would be my first idea on how to fix this problem, either a custom nut or a custom bottom bracket. Second would be sourcing the correct size assembled motor and selling the incorrect one on the used market, and third option being a full tear down and reassembly with the proper motor housing.

 

[kungpho]

I was able to find the housing here but I agree that it's probably not worth the time/money. The shaft would need to be changed out as well.

About 8mm of thread is exposed with the current motor, so enough for the Lekkie One Nut to feel decently secure, but not enough to install the fixing plate, so some amount of rotation is going to happen. I can probably throw together some kind of stabilizer system though, e.g. by modifying or copying this one.

I do wonder if I should consider moving to a BBS02, which would save me a bit of ground clearance. Although now that I'm looking at it, it seems like that model is not even offered for a longer bottom bracket, and I see conflicting info online about 52V compatibility.

 

[neptronix]

You're off to a nice start. I once had a Turner O2 with a 4-6kw hub motor on it, it was the best ebike i've ridden to date. There's magic in these frames' designs, so i wish you the best with your conversion.



Sorry i can't help answer your question. My thought is, for full enjoyment of said DH bike, if the BBSHD doesn't work out, maybe a higher power mid drive like a CYC would work out, expanding your BB size fitment options. I also think, your Turner could probably gracefully handle higher power.

Personally if i could do it again, i'd run a 'lightest bike' mid drive on one of these for maximum adjustability if 1kw is good enough. CYC Pro 2-4kw drives if i wanted gobs of power ( probably! ).

 

[kungpho]

Nice bike! that looks rippin'.

Yeah these Turners are very cool bikes, you can see that a ton of love went into the design. The engineering/machining of the linkage and shock tunnel is very impressive on this one... and it has DW link suspension, which is generally seen on trail bikes and rare on DH bikes, and which yields an efficient pedaling platform. So overall it should be perfect for my purposes.

 

[Tyler5883]

I built a secondary motor support for mine because I didn't fully trust the locking plate it came with. Looks like something like this could be a potential for you maybe, but youd have to be the judge of that. Maybe you could connect one end to your shock bolt in the center of your frame, possibly needing some spacers to accommodate any clearances needed.

You can see in the pictures, the bolt for my motor had to be spaced out with washers, but I will be getting the proper shoulder bolt and making a solid spacer for it, so it won't bend. You'll also want lock nuts on the turnbuckle which are not shown in these pictures.

Sorry the pics aren't that great, can take better ones tonight after work if you need more.

 

[Diggs]

I always thought (and I could well be wrong) that the shock reservoir is mounted on top to be sure any air bubbles stay out of the shock itself.

...and just to spur some thoughts, this is the way I stabilized my BBHSD. I thought about installing a Rivnut but went with a pair of hose clamps.

 

[2old]

I do wonder if I should consider moving to a BBS02, which would save me a bit of ground clearance. Although now that I'm looking at it, it seems like that model is not even offered for a longer bottom bracket, and I see conflicting info online about 52V compatibility.

I've been running one for nine years @ 52V without difficulty.

 

[kungpho]

Update! I got a new bracket designed and machined. Not pretty (been a long time since I've used the office CNC), and I bodged a few tolerances that had to get dremelled out, but a definite improvement over no support.



The idea is a bolt and captive nut sit against one of the pockets in the frame, limiting rotation towards the wheel. The slot allows for a bit of adjustment as my angle measurement was lifted off of a photo and is not particularly precise.

I also changed out the chain ring for this one, which has improved the chain line significantly.


Additionally, while the current battery is a pretty decent fit, it sags quite a bit under full throttle and I'm not very impressed by the capacity. So, I started working on new battery design. Aiming for 14s7p 18650 cells. Currently thinking about the best way to attach it to the frame semi-permanently, so that I don't have to worry too much about someone yanking it if I leave the bike locked up.


And finally, I am eagerly waiting for some fenders to arrive... the bike has been a huge blast to commute on so far, but when the road is wet the constant spray into my face is a bit of a biblical experience to say the least.

 

[NexGen3D]

Update! I got a new bracket designed and machined. Not pretty (been a long time since I've used the office CNC), and I bodged a few tolerances that had to get dremelled out, but a definite improvement over no support.

View attachment 361659View attachment 361662View attachment 361658View attachment 361663

The idea is a bolt and captive nut sit against one of the pockets in the frame, limiting rotation towards the wheel. The slot allows for a bit of adjustment as my angle measurement was lifted off of a photo and is not particularly precise.

I also changed out the chain ring for this one, which has improved the chain line significantly.
View attachment 361660View attachment 361661

Additionally, while the current battery is a pretty decent fit, it sags quite a bit under full throttle and I'm not very impressed by the capacity. So, I started working on new battery design. Aiming for 14s7p 18650 cells. Currently thinking about the best way to attach it to the frame semi-permanently, so that I don't have to worry too much about someone yanking it if I leave the bike locked up.
View attachment 361665

And finally, I am eagerly waiting for some fenders to arrive... the bike has been a huge blast to commute on so far, but when the road is wet the constant spray into my face is a bit of a biblical experience to say the least.

Go 15s4p with 2170 cells, Samsung make some nice 5000mah ones that do 25amp continuous, 15S will give you 60v SOC and the BBSHD along with the Ultra Max work fine with this.