20" Stelber tank bike- beefy BMX build

[Fisch]

I picked up this little guy as I have really been enjoying riding my 20" Yamaha moto-bike BMX lately. Specifically I really wanted a 20" tank bike to build into a beefy BMX. As if a BMX existed in the 50's.

This is a 20" Stelber balloon/tank bike.

I did this mockup in Photoshop to illustrate what I am chasing.

There will be challenges though. SO much so that I wonder if I would be better off starting with a different 20" tank bike.

The first problem is the pedals/cranks. The bottom bracket is so small, and is a pressed bearing design. There is a small chance modern sealed BMX cranks might fit in this bottom bracket. The diameter looks close, but I am doubtful it is a match. Certainly not english 3-speed size (too bad).

The next problem is the head tube. It has that one piece kid handle bar setup. But I am hopeful this will come apart and I can just put new bearing cups and guts in it.

Another challenge is the seat tube. It has a very skinny post in it and I pray that the bushing or whatever shoved in there isn't brazed. Anyone mess with these before?

Other 20" bikes from the era that I see have 'normal' cranks, bars and seatposts. But it is hard for me to find a 20" tank bike at all. Especially with a curved middle bar. Just gotta decide if I want I want to be patient and start with something that is easier, or dig into this rusty nugget. I have a lot of unfinished projects as is! :mrgreen:

 

[Fisch]

I am not sure but I am guessing this bike dates about 1955 based on this ad, though pictured is a 24" I think.

 

[enbro]

It's a cool idea...how about some rear shocks like an early BMX...the kind with the fake gas tanks (like your bike has). See other threads I've posted in to know what I mean.

 

[Fisch]

I've thought about that too. I have a 20" 2-shock swingarm from a 70's Moto-BMX. But the shocks usually connected to a bar that went out over the tire.

I was just looking at vintage monoshock set-ups too. Like the old Webco stuff. Some old Webco mags would really take this thing over the top.

Some modern monoshock BMXs seem to have a bottom bracket built into the swingarm to keep chain tension. That is a thought too.

 

[Fisch]

So it turns out the bottom bracket on this Stelber is just about a match for a Spanish style BMX BB. O.D. of the bearing would be 36mm-37mm which is close to the spanish pressed bearing. I think the housing/tube is longer than a standard BMX one, but a sawsall can fix that.

The spindle in the stock bearings is 16mm. Too bad it wasn't 19 or 22!

I also got the handle bars/fork out, and sure enough standard bearings/forks will fit. So that is cool.

Still unsure about the seatpost situation.

 

[Fisch]

Still tinkering with the Stelber. To get that classic look I am thinking of a truss fork now. Also it will be lighter, because I am tempted to turn it into an E-bike. The round electric motor would be pretty sweet in that unique drop loop frame. The batteries hidden in a vintage lunchbox on the rear rack.I already have a 20 disc brake front and dual drive rear wheel from a 20" electric BMX. And the electric stuff (but the controller and/or the batteries are shot.)

Also grabbed a fat pair of Demolition Momentum 20X2.35 tanwalls for the project.

 

[gcrank1]

It screams mini 'board tracker' to me........