G4 and sickbikes shift kit

It will work with the 5/8 shaft HS or Honda motor and the thinner 4G gear box.That is the set up I run and a few others.As far as the wider 4G and the shift kit I'm not to sure.I run 17-10-36 to 14/28 freewheel

I've been riding a SBP 4-Stroke Shift Kit for over a year now, and during that time I've had it set up with the Grubee III Gearbox (3.7:1 reduction) and now the Grubee 4G for Honda Belt Drive (5:1 reduction). Both of these Drive units come with 11t freewheel output sprockets as standard equipment. There is a 10t fixed sprocket and shaft available for both drives as an option as well. When I ran the Type III Gearbox I used the stock set-up on the Jackshaft which is a 17t driven on the left side and a 9t driver on the right side. The Chainrings were a 48t driven and a 36t driver (30t chainring is the default/standard driver for the chainrings) to the rear cassette. When I switched to the 4G Unit, I changed the 9t driver on the right side of the jackshaft to an 11t driver and I changed the 48t driven chainring to a 44t. SBP recommends the the output of your reduction unit should be fixed (non-freewheeling). I made my 11t freewheels fixed sprockets by welding up the seam between the sprocket and the freewheel body, rather than switching to the 10t fixed sprockets from Grubee. Right now there seems to be no 4G drives available. The latest drives from Grubee are available in three different ratios? My guess is that bicycle-engines will probably be bringing in only one the 4:1 unit and maybe perhaps offer the other pulleys for purchase as parts?

ocscully

Hey primusbike, I've run a 4G with shift kit since last summer. I've used 30/48T and 36/48T crank sprockets, switching to 44/44T next weekend. I've also tried 9, 10, 11, and 14T on jackshaft output. Currently using 10, might switch back to 9 next weekend.

I've thought about the belt idea a few times last year, came to the conclusion that it would take more machine work than it's worth. I almost tried it tho, it's really just a pair of cogs and maybe a new 4G output shaft. Thing is, you'd lose freewheel. Some don't like the freewheel, but I do, since I pedal with engine off a lot. Of all 3 chains on the setup, the one I've had the least problems with has been that 12-link from 4G to jackshaft. Therefore, I've left it alone.

primusbike said:

Okay, one step further, what about eliminating the need for the jackshaft in the G4 transmission? Okay, if you were to schematize the power train there are 3 jackshafts to transfer rotational energy to the rear wheel.
1. jackshaft in the G4 (bearing in aluminum)
2. Jackshaft in Sickbikes kit
3. Free wheel/pedal crank. acts as jackshaft

What if you chop the G4 down the center, so the two bearings could be moved further apart. Use a bandsaw and cut it in half. Put the two pieces on a table measure and cut a plate of aluminum to reinforce the two back together. Attach the G4's larger wheel to a 5/8 rod long enough to go through the bearing and the other 2 bearings carrying the jackshaft. Obviously using a bigger belt.

Click to expand...

This idea has been done. See link to blog. Alot of good information here nashmoto | blog

ocscully