Framebuilding for Motors



I bought a 20" Worksman bicycle for use with a motor kit, but the frame turned out to be too small overall and I didn't quite like the design much, so I decided to build a stretched board-track style frame from scratch.

The question then was if I should cut up the Worksman frame for its head tube and bottom bracket, or if I should just go buy raw parts and sell the frame (I had successfully bent the rear end to accomodate a Golden Eagle drive ring). I felt like it was a waste of money to cut up a good frame when I knew that bike parts could be bought for just a few dollars each.

When I measured the Worksman tubes and began comparing them to what I could turn up online, I found that the Worksman tubes were considerably thicker than anything else I could find. The Worksman head tube outer diameter is 38.5mm, and most 1-inch head tubes I found online were between 31.7mm and 33mm. The Worksman BB tube (a BMX type) was 58.5mm O.D., and I didn't find any that were bigger than 56.5mm. The bottom bracket doesn't really need to be stronger than usual but it's a good idea if the head tube is, seeing as this bike is going to cruise at twice what it would normally do if pedaled.

If you had a bicycle framebuilding business nearby maybe you could easily get some thicker tubing and take it to them and have them finish it for you, but I have seen in the past that typical automotive shops don't know anything about making bicycle parts and don't want to be bothered. So it looks like the brand-new shiny Worksman frame is headed for the butcher block.

...Another thing I found was that many of the places that sell framebuilding parts are oriented towards building conventional upright road and MTB bikes, so they don't sell loose parts, they only sell entire tubesets for building a whole frame. The tubing is butted so you can't very well cut it up and use the smaller pieces, because it's thinner along the middle lengths than on the ends. And most of the tubesets are for lugged fittings, which makes things much easier but rules out any sort of unconventional frame geometry.

just for kicks

I have thought about building a frame from the ground up with the engine as the main work around and go from there but I still have a lot to learn so I'll hold off a bit.

I think if I were to do it I'd have to have a decent front suspended fork set, and a rear suspension that works well with the engine and can still be pedaled, a built-in-the frame fuel tank.I'd try to build a jig just so it comes out best and would be repeatable.

Good luck on your project it sounds very interesting.



Just a couple ideas I'll bounce off you if you are making a totally custom frame
for an engine powered bike....I wonder how easy it would be to build a frame so that the fuel tank is inside the structural tubes AND make some of the frame
an actual tuned pipe?...

Also, a full suspension would be nice!



...I wonder how easy it would be to build a frame so that the fuel tank is inside the structural tubes AND make some of the frame
an actual tuned pipe?... Also, a full suspension would be nice!
--The engine I'm using is a 4-cycle, so there's not much use for a tuned pipe.
--Enclosing tubes isn't difficult if you're building from scratch, but the style I want has a separate fuel tank anyway.
--I have a springer fork I like in mind, but don't plan any rear suspension. It's a lot more trouble to do.


Local time
11:58 PM
May 15, 2008
right here in Ohio
custom frame

If you didnot pay to much for the frame go ahead and cut it up. other wise try a machine shop to bore your head tubes and crank tube parts.from stock dom tube.
use as much as you can from your works man frame its good solid stuff.