Furry, I actually built my own shift kit for a 48cc China Girl. Can't find any pictures at the moment but used 1/4" steel for the jackshaft frame and press in bearings. It worked well, but didn't increase speed or acceleration any beyond the standard single speed kit. The jackshaft kit had more drag so I found I actually needed the gearing more. It was better for slower speeds and off-road. Raising engine compression made it harder to kick start and eventually stripped the one-way clutch. Keep the compression down for the shifter bikes.
I was planning on making an aluminum jackshaft frame but never did. It would have saved a pound or two. I did drill the devil out of the steel frame, which helped. I think I used 5/8" shaft which is overkill. 1/2" or hollow or alloy tube would be fine. #41 chain was ample. I probably have a thread on here detailing that build from about 3 years ago.
I'm living in the city now. Still dreaming about a gas/electric hybrid that could discretely cruise green lanes, while still able to cover long distances on gas, maybe even charging while doing it.
You know, I'm just trying to keep
Shift Kit capitalized, to the credit of the forum members who gave it to us and to highlight
the importance of dreaming.
I want our members to
remember this was
our story that happened right
here on our forum, about our hobbyistic daydreaming turned into metal, and the story is still here in the threads of discussion and daydreams and dreamy builds.
You can go back and read the whole of our forum and see how the dream progresses through time, and where we have been, where we travelled through, where it comes to now, to know where we are right now and where we're dreaming about going next!!
Newer members
should know that they have a debt of gratitude for those
two innovative dreamers who gave us
all the possibility to try the Sick Bikes Parts
Shift Kit and its associated products.
Use the Shift Kit and its parts in
all the sick and dreamy ways
you can dream of, and let's keep the sick dream going!
Yep, a
dreamylight aluminium box frame holding the shaft very rigidly, can have less flex for a similar weight as mild steel plate construction, or vice versa.
It might be easier to shape and drill initially at home, but then it needs to be welded professionally, and then it
requires the heat treatment procedures that are
essential before it becomes the stiff and light construction we dreamed about.
(so beyond
realworld hope that I can use alloy box for any of my
realworld builds, hence
dream builds thread).
Idk
how you drilled accurately for the jackshaft bearings or how you keep them in place...
biggg arse drill stand..? Put collars on the shaft or you found a lathe person who could make the cups and caps... like QR15 front hubs? I would love to see
what can be dreamed up to prevent any binding and make it a simple assembly?
Did you use the Z arrangement of the Shift Kit? There are other arrangements that you can choose, should you
dream to do so!
I would love to see the Y arrangement on my dream fat-hybrid-beachbike build, the
50SAND (
realworld build thread starter almost nearly imminent!) as the 2T ICE powertrain in Y arrangement would have only
two chains and
four sprockets instead of the three and six in a Z arrangement.
That is why I need the assistance of an independent welder fabricator who can make the box to hold the (standard threaded 73mm BB shell?!) shaft bearings, far enough out to the rear of the engine's output sprocket to make the room to fit a large enough sprocket on the LHS of the shaft. This first chain reduction going to the shaft which must now bear far greater torsion at a much lower RPM, huge twisting stresses we can only dream of, far greater than it would have in the classic (and intentionally far more universally compatible) Z arrangement. But the Z arrangement has those same forces,nor perhaps even greater, at it's own bottom bracket. In fact the Z arrangement with two reductions and then a multiplier is a trade off (more than most people stop and think about imho) of efficiency and stresses on the frame against a universal system that anyone can bolt into most bikes with few tools and no modification of the original bicycle.
Imho. You want efficiency over everything to hit your specific target speed or power output, then yes indeed you begin with your own dreams, and then you build single-mindedly and you use the parts from the SBP Shift Kit, but you do it in your own way.
I
know you can't build a damn thing without daydreaming all that through first, several dozen wonderfully enjoyable times beforehand lol.
No reason not to, because it is fun to dream and it's a fun dream, and we're allowed to be dreamers.
Its actually even
our duty to dream the dream because daydreamer believers like us lot on motoredbikes.com are
bloody good at it!! 
☝
I would have the dreamy hollowed out, keywayed, 5/8" mild steel shaft, case hardened just enough to be less brittle than the woodruff key.
I am 100% ready to order a dreamy jackshaft of my own, custom length, custom partially hollowed, and a little custom internally threaded, 5/8" keywayed shaft
in the real world ....
but since the UK's Covid19 response is like the
hugeeesssttt summer bank holiday weekender-on-a-bender, the company is listing all their products out of stock. My beautiful dream turned nightmareee!
Charging while it drives, now that
is a literal
dream build.
comes.
