Shifter for 4G ???

Well, only 3 people have done it successfully so far that I know of. Myself, ocscully, and MotoMagz. No one's done a build thread on it, because there isn't much to document. How I did it was buy a non-tapered shaft Huasheng, aka the "5/8 shaft" engine and a 4G for that engine from bicycle-engines.com. Then I bought a 4-stroke shift kit from SBP. Then I kinda bolted it all together and ran it through my 3-speed Sturmey Archer hub.

18 months later, it still works, but I'll tell you right now: a shifter 4G is very rewarding, but also can be very difficult to set up and maintain. It's not simple like a Q-matic at all. You have 3 chains and significant drivetrain slack as a result. You may have to run dual spring-loaded tensioners on 2 of those chains to keep everything operating smoothly. The system will be very direct, if you are not gentle with the throttle operation, you will tweak the motor mount and maybe something else. It will wear out chains faster than most other systems. It will also amaze you with it's acceleration.

If you're already used to a 4G, you have a third of the battle won, tho. The rest is patience, and a bit of your own ingenuity.

Heres a build using a 4G, just a basic bike but worked out well. http://motorbicycling.com/showpost.php?p=297162&postcount=1

I had forgotten about cannonball2's nice build. Sorry, cannonball2!

No problem, cant keep up with all of em!

ya forgot about nashmoto too!

nashmoto's 4G NuVinci shifter came in 5th out of all the 66 cc 2 strokes at the last Grange race.

NashMoto's great build is quite a bit different and on another level tho, that's why I didn't include it.
He lacks a reduction jackshaft compared to SBP's and cannonball2's, and his really isn't a 4G anymore per se

His overall ratio appears to be set extremely tall, you'd need extremely low gears on the rear wheel (NuVinci goes down to 0.5:1 itself) to use it.
You'd also need a lot of power (or a nice downhill) to use the NuVinci ratio on it's high end.

I asked the crew at SBP about using their 4 stroke kit:

Hi,

I have a 5/8 shaft HS engine with a 4g T Belt transmission. Can I use this set up with your 4 stroke shift kit? In looking at the pictures it looks like it might work, but is there something I'm missing? I like the idea of being able to use my 7 speed deraileur system.

Thanks for your time,

And got the following response:

Bill,
As long as it is the 4G for the 5/8 shaft motor you are good to go.
Thanks,
Jim

It sounds like their kit will work as long as you have a 5/8 straight shaft engine and 4g kit.

Mine was a taper shaft 4G, but it was a custom build based around SBPs parts.

You can build a shifter 4G bike with the tapered-shaft version hardware, but you may have to run extra-extra-wide crank arms or extra-short arms.
Notching the engine mount slots is a possibility, too.

The SBP arms and spindle are 9.5" wide between inside crank arms at pedal location. The straight shaft setup with 4G cover mounted is 9.5".
I shaved some of the cover mount so mine's 9.375". The tapered shaft setup with cover mounted is 10-10.5" wide. Gotta get creative with that one!

I just used the stock Grubee pedal set for the 4G that came with it. I turned the spindle to fit the SBP freewheel adapter. Requires very little removed. Could be done farily short order with a strip of sanding belt and a bit of care. Almost exactly the same effort as making a 5/8 clutch fit a Preadator. I then drilled a hole about 1/2 way throught the spindle and locked it with a hardened allen bolt since the adapter uses a key. The spindle only puts a load on the allen when pedaling as its stationary most of the time. Its not difficult to use the tapered shaft G4 kit with a bit of tweaking.