Monday, June 18, 2012

Yang Frame

A few people have asked about the frame mods on Yang Yang and why I did it. The idea was to change the geometry of the chassis to fit a more compact, racing stance but keep it subtle enough that most lay persons would never notice. If someone wanted to build something similar it wouldn't be as easy as dropping the front end and putting a tank on. Up till Yang, most of my frame mods I did were either by eye, or making a one off jig. Welding the frame to a table, or using my pals JD's jig. While JD's jig works well, it didn't have some of the features I really wanted or needed so it was time to build my own. I would have loved to have super heavy CNC machined steel, but money, time, and foot print are serious issues. So, I have to get materials I could easily work with in my shop, and wouldn't break the bank. Funny thing, making a jig with 5k or so and precision machine steel would have been 10 times easier.

My Yang build started out with a calender. I wrote down dates that I needed to meet in order to get the bike done. Making everything even more difficult, I was working a film project till just a few weeks ago, so I did 10 hour days at work, then 4-6 hours in the shop. Yang has been largely a part time project. Three weeks in to my build calender I am just finishing the jig. The stress was already starting. Matt Gamble gave me hand crunching some numbers on the motor mount base. When all was said and done on the jig, I'd hold it up to most jigs out there.
Once the jig was done, it was time to chop! Initially I was going to lower the neck a full 2" but after measuring 100 times, I decided 1 3/4" would get me where I wanted and keep the backbone and cross strut mods less extreme. The rake would stay stock.

 Initially I thought I would replace the backbone and strut at the neck, but found a much easier solution that worked probably better. I pie cut the backbone and strut right at junction of the neck, then I could bend it slightly to meet the new angle created by dropping the neck. Slugged it, plug welded it. The backbone had the be knotched to clear the rear rocker box.

The seat area was narrowed slightly. This was simply done by bending some new pipe and locating the bend more towards the rear. I reused the castings by shaving them and rewelding. 
The end result is something most will never see, but it changes to look and stance of the bike significantly. Jig took 3 weeks of nights to build, the frame mods took 2 days!

More to  come.


  1. Fantastic rundown, so in the final analysis, how much shorter is the overall wheelbase ?

  2. thanks for sharing Caleb. it's cool that you're willing to share these details. these are the changes that really get the look spot on. this thing's gonna be tight, can't wait to see it finished!