Shimming BB30 mid drive to fit American BMX/Cruiser Ashtabula bottom bracket

Aug 22, 2018
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Only one chopstick hammered, cause I still need to get back apart to fix another issue. You can't see from this pic how the inside face levers badly because it isn't flat. A ring shaped depression seems paradoxically intended to center and straighten it on a BB30. That unsupported void needs to be filled with: I dunno, JBWeld probably. Tight packed with sticks, the void might be less of a problem, but no reason to chance it.

Luna and Bikewow are rumored to have made adaptors to do the same. The Bikewow version has a ridge that seems intended to allow clamping force to reach the bottom of the void all the way round. Not putting all the force on a small part of the face way off center and above. I'll post a pic of that problem later, and it will make more sense.

Motor is Tongsheng. Bottom bracket Electra.
chpstx.jpg
 
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May 10, 2016
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Since you’re running a square taper bb, there are adapters on the market that press into the bb30.
On a road bike a few years back that had a bb30 shell I used a praxis adapter to run sram cranks. I believe praxis, problem solvers, and wheels mfg have various adapters available for a bb30 shell.
To me it would seem the chop sticks wouldn’t provide a ‘level’ bb. And would also potentially shake loose. Also using jb weld to fill the gap would creat issues if the bb ever needed to be serviced.

Cool conversation tho. Bb30’s are a good idea on paper, but tend to squeak and be unnecessary with so many other interfaces available.
 
Feb 20, 2018
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There it is, Luna Cycles. I don't know if they are available again, but LC were preparing another batch.
The chopsticks will eventually wear out. If they get wet often even faster.

20181006_173537.jpg
 
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Aug 22, 2018
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Also using jb weld to fill the gap would creat issues if the bb ever needed to be serviced.
The void I need/intend to fill with JB isn't inside the bottom bracket. Isn't going to interfere with service, but a shim to protect the chainside of TSDZ2 motor housing from cracking under poorly distributed stress.

Dude on the sphere had to weld (aluminum/zinc?) his back together after it broke all the way across. Don't want that happening to me.

ChainsideBikewow.jpg


Only the area marked in red clamps against my Tongsheng inside face. Prying away at the face to no good purpose. Bikewow's ridge (highlighted in green) meets closer to the way it should fit BB30. Therefore the red mark on this adaptor is not something to worry, but solved. Luna has no ridge, and probably fits better with Bafang.

Just wanting to fill mine flat like Bafang, to work with Luna or sticks, not to bond anything. BB30 shaped depression can be filled off bike. Could use mold release, or not hard to burn away with a soldering iron, if marks are no concern.

Void between sticks is something else entirely. I might darken them with a sharpie, then seal the exposed ends with black RTV. But no intent to squeeze a bunch inside the bracket, especially not knowing how often those sticks might want replacement.

Screws might be an alternative to pounding-in the last few sticks. Just make sure not too long and possibly damage the motor.

------edit------

Has come to my attention that Bafang 01/02/HD aren't flat and share a similar shaped depression. Lingbei GP may be a little closer to flat. Unclear if its cone and bumps are completely inside/outside the offset radius of an American bottom bracket, but looks like they could be...

All of them look adaptable with a shim or filler.
 
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Aug 22, 2018
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This is what I've done to prevent mine from rotating.
Had no hole to mount through and didn't feel like drilling...

motormount.png
 
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Aug 22, 2018
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Hopefully enough contrast to see where I filled in the depression with JB.
Due to unavoidable offset from center, 2" BB does not fit in the depression.
But instead levers on a raised ridge far away from the motor and nothing
but void on the near side. Shim or fill here can give 2" BB a complete ring
of contact and relieve bending stress.

jbshim.png
 
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Aug 22, 2018
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Shamelessly ripped form the Sphere, this was Casainho's disaster.
Though his TSDZ2 failed by rotating into the frame, its the same
weak point I'm trying to protect.

casainho.jpg


Again not mine, but Kizasul's fix after his broke in much the same way.

Kizasul.jpg


Doesn't happen to everyone. But slapdash mounting decisions can place awkward
stress on the TSDZ2 case. Which is why I had given mine some extra forethought.
 
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Aug 22, 2018
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From the topside, a bit easier to see why the motor mount required bands.
Simply no place to bolt through without opening a rusthole in the frame.

Definitely sealing the exposed end of those chopsticks with black RTV.
Not to glue them permanently, just to keep water from splashing in.

ratback.png
ratfront.png


Tiny battery is for the headlamp, not the motor. Much work still in progress.
 
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