Adding the Bafang Ultra Max to a Frame

April 16, 2019

Before we get started, adding a Bafang Ultra Max to a frame will involve welding, so if you don’t weld, or…you don’t know someone who is good at it…this might not be the article for you. If you are wondering why someone would go to a lot of trouble to add one of these drives to a frame that they have, you can take a quick scan at our article on the “Big Dog”, by clicking here.

Let’s Get Started!

There are a handful of bike models from existing companies that will sell you an ebike with the Bafang Ultra Max mid drive. However, if you don’t like any of those particular models, it is possible to weld one of the mounting shells onto a frame that you like (or a frame that you already have).

This builders name is Gordon, and he is from Brigantine in New Jersey, on the east coast of the USA. He decided that the Minnesota 1.2 aluminum fatbike frame was the perfect candidate for an Ultra, and fortunately for us he decided to document the process of cutting and welding-in an Ultra drive.


The Minnesota 1.2 aluminum fatbike


The “a la carte” Ultra drive and it’s mounting shell.


Luna Cycles in Southern California is currently selling the Ultra drive by itself (no frame) along with the proprietary mounting shell. Once Gordon saw this, he snapped-up one of them while they are still available.

Building the Jig

One of the reasons I was drawn to this project is because…even though it documents an Ultra drive installation, the same principles can be applied to other drives as well (Bosch, Yamaha, etc). That is something that comes up in discussion on occasion, and this build will give you an idea of what is involved.


Fortunately, the Ultra’s ISIS spindle is hollow all the way through, and has an almost perfect 1/2-inch ID. By inserting a tube, he can precisely locate the spindle location and alignment after he brutally chops off the bottom-bracket with no regard for its’ screaming…


Installing two plastic bushings for alignment.


With the spindle and bearings removed, Gordon used machine tooling to create two plastic bushings that fit perfectly in the bottom bracket shell, which also had a 1/2-inch ID hole for the alignment tube.


Adding several clamped steel plates for welding the jig braces.


The pic above is one of the most clever parts of this build. I’m sure there are several ways to attach a custom alignment jig to an aluminum frame. However, if you know how to weld, and you own a welder, steel is the cheap and available material of choice.

The problem is that, since this frame is aluminum, Gordon needed to clamp some steel plates over the frame tubes. Doing it this way ended up working quite well. It may not be clear just yet, but you will see just below what I’m talking about.


The custom alignment jig.


The pic above shows the steel braces that are welded onto the clamped steel sheet metal plates. It’s a little like my girlfriend from high school. Not very pretty…but she works great.

Making the Cut

It is VERY easy to screw up the next part if you don’t have a rigid and stable jig. I’d cut the tubes a little long, and then trim them little by little until I was finally able to insert the mounting shell.


Cutting out the bottom bracket


Marlon Brando as Vito Corleone from “The Godfather”, part-1.


The venerable bottom bracket, RIP. I will call you…Sonny Corleone.


If you cut away too much, you have to find a way to fill-in the gaps.

Welding it Up

One good thing about using aluminum for the two parts that need to be welded is…aluminum is fairly easy to shape, so you can get a very good fit before you start welding. Also, after the welding, you can even sand the welds smooth, if you want…


The well-fitted downtube at the joint to the mounting shell.


Another well-fitted joint at the base of the seat-tube.


You can see here how the 1/2-inch aluminum tube keeps the spindle in the original location and alignment during the welding process.


A very nice example of TIG-welded joints.


The two chainstays also got some hot TIG-love.


The welding part goes fast, but the custom jig building takes a long time, and…that time is well-spent if you want good results.


As much as I like a sweet paint-job, I am also an old hot rodder who has frequently used a dull and dark primer as the final finish.


The finished project


I would highly recommend to anyone with a hardtail frame to get a suspension seatpost, like the Suntour NCX or the Thudbuster (click here). Brigantine in New Jersey is on the beach, so it’s no wonder Gordon wanted a fatbike.


At the beach on Gordons Ultra fatbike

The Original Build Thread

I always ask for permission before I write about a custom build, and if you want to see the original discussion thread about this project, it can be found by clicking here. Gordons username is “Flash-FX”.

Written by Ron/spinningmagnets, April 2019

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego. Hydraulic mechanic in the 1980's/Los Angeles. Heavy equipment operator in the 1990's/traveled to various locations. Dump truck driver in the 2000's/SW Utah. Currently a water plant operator since 2010/NW Kansas


Leave a Reply