So... How much should I Dremel this bottom bracket?

[Scott_J]

I'm attaching a Bafang 8FUN to a SCOTT Aspect 29er.

The motor slides in OK, until it hits the middle ridge.
I need to take less than 1mm from the inside of the bracket (see pic attached).

I've tried grease and the ol' rubber mallet, but alas to no avail.

My question is: How much would/have you taken off to fit a Bafang motor?

Thanks in advance.

 

[Nealh]

It will be a bit of over weld stopping it sliding all the way in so just go carefully to remove what is needed some time a half round file will do the job.

 

[Scott_J]

Thanks Nealh.

I feel I have a long day ahead...

 

[Ocsid]

Is there any merit in using a cheap, electric drill driven cylinder hone?
LINK

I would add, it is not a task I have done, but just musing on how I might do it if I needed to.

Identifying what needs Dremel attention, if going that route, would be something I would try to resolve before attempting the task. I think I would turn a wooden gauge, and wrap it with a trailing piece of wet and dry, or from my shed use marker blue on paper, to identify the high points.

 

[Nealh]

I had similar as most likely a lot of others will have had, my BBS wouldn't slide through so a rat tail file came to my rescue and after 10/15 mins off filing the job was done.

 

[Scott_J]

I had similar as most likely a lot of others will have had, my BBS wouldn't slide through so a rat tail file came to my rescue and after 10/15 mins off filing the job was done.

I wish mine was as simple!
I've spent all day on this and it still won't go in...

 

[Kinninvie]

I always use a Dremel .Take a bit off then try it.
If it doesnt go do it again until it does.
Also make sure you loosen the cable guide bolt underneath first as I have known them to get in the way too.

 

[cannon]

Is it possible to see what is stopping it from the left hand side ??

 

[Scott_J]

Nope to all of the above, I'm afraid.

It would damage the bb thickness to such an extent, that the stresses on the frame would be too much to bear!

 

[Scott_J]

Is it possible to see what is stopping it from the left hand side ??

Nothing is stopping it, apart from the inner thickness of the frame's BB.

 

[Fordulike]

Nothing is stopping it, apart from the inner thickness of the frame's BB.

IIRC, the Bafang axle housing that slides into the BB is coated in a layer of paint. Do you think sanding that layer off, might give you some extra clearance?

 

[Gringo]

do you know any engineers ?
If it was my bike I’d strip it down to just the frame, put said frame on a milling machine and bore it out to size.
Alternatively, I’d spend a few hours with a drum sander in a pistol drill !
https://www.toolstation.com/drum-sanding-kit/p15110

 

[MontyPAS]

Is that an alloy frame.
If so it is not going take much to file it down with a half round file, and finishing with a suitable flap wheel

 

[Scott_J]

Seriously, thanks for all the suggestions, but the frames BB thickness would be down to a scary minimum if I was to continue!

I ain't chancing it!

 

[MontyPAS]

Seriously, thanks for all the suggestions, but the frames BB thickness would be down to a scary minimum if I was to continue!

I ain't chancing it!

There is plenty of alloy there, I've done it on a frame no issues!

 

[Ocsid]

Dare you work a tap in a little further, LINK ?

Its lead in section, will bore, true and in line, only where the excess metal you need to ease away is.

 

[MontyPAS]

If the O/P is fitting a BBS01 then the thread is redundant so cheaper, easier, and safer to just file to fit.
Most sealed BB's are stepped, that's why the extra meat has been left in the BB section.

 

[wheeliepete]

Seriously, thanks for all the suggestions, but the frames BB thickness would be down to a scary minimum if I was to continue!

I ain't chancing it!

How about all the frames with a BB the BBS fits through? Never seen or heard of a BB failure due to wall thickness. The amount you need to remove is mimimal, prob. less than .5mm, get filing, your worries are unfounded.
Ocsid's idea of a cylinder hone is good, or a flapper wheel, it will remove a nice even amount of material and leave the BB with an even thickness.

 

[JPGiant]

Use internal & external micrometer's to compare dimensions of Bafang motor shaft o/d and BB (inside & outside) to determine how much metal you have to deal with.
Then hire/buy/borrow a hand operated taper reamer to open up the bore in stages.

 

[MontyPAS]

Use internal & external micrometer's to compare dimensions of Bafang motor shaft o/d and BB (inside & outside) to determine how much metal you have to deal with.
Then hire/buy/borrow a hand operated taper reamer to open up the bore in stages.

Or just use a file, job done!
Why overcomplicate things...... Just sayin!