Jackshaft pedaling vs motoring

GoldenMotor.com
knightscape

knightscape

Member
Jul 29, 2013
340
1
16
Maine
Please forgive what may be a stupid question about jackshafts, I've been searching and not finding what I'm looking for... The bike I'm looking to set up with the kit I'm tinkering on is a rear-deraileur geared bike with disc brake and a single front chainring. I'd like to get a jackshaft set up going to take advantage of the gears and lose the scary stock tensioner and ragjoint to allow the disc brake. Here's the question: Is it possible to set up a jackshaft such that when you are actively pedaling without the motor running, you are not turning the engine's drive chain? From what I've been reading, the answer seems like a "no", is that right? You need to be turning the drive chain (via pedaling) to start the engine? If so, is there an alternate way to do what I'm looking for? I'd like the ability to pedal without any added friction in the drivetrain, but then when I want to motor, to engage the engine and let 'er rip. Motor is a 2-stroke of unknown (49-66?) cc's. Also, perhaps I've got something out of whack with my set up, cause I am new to this, but I can definitely feel the added drag when I am pedaling with the clutch disengaged, it's not a ton, but its there. I'm looking to be able to completely ride the bike like normal, but then crank up the engine for quickly covering ground. Am I making any sense?
 
Sidewinder Jerry

Sidewinder Jerry

Well-Known Member
Dec 19, 2011
2,008
949
113
61
Rockwood, TN
The Staton shiftkit uses two freewheels. Therefore the engine and peddles drive the rear wheel independently. Staton setups use a gearbox which has a centrifugal clutch. A pull cord is used to start the engine. One could adapt an electric starter and reachable gas primer for on the go starts. I do realize this may not be the answer you're looking for but it is a way to do what you're asking about.
 
knightscape

knightscape

Member
Jul 29, 2013
340
1
16
Maine
Nah, that makes sense, thanks! I think I may have to rethink what I want to do with the project I've got in mind. Probably need to put the cart back behind the horse and get my motor running on a solid set up on the bike it's on right now before getting too funky.
 
M

mkatt4x4

New Member
Aug 30, 2013
65
0
0
Canada
I have been looking at jackshaft kits, but now I run across this term gearbox. So a gearbox is a transmission right, and I can buy one for my Grubee slant 66. What does a gearbox do to my bike? How does it operate? How many gears do I have? Total Newbie questions I know, search and youtube didnt yield much info.
 
MotorBicycleRacing

MotorBicycleRacing

Well-Known Member
Jul 28, 2010
5,844
109
63
SoCal Baby!!!
www.facebook.com
mkatt4x4 said:
I have been looking at jackshaft kits, but now I run across this term gearbox. So a gearbox is a transmission right, and I can buy one for my Grubee slant 66. What does a gearbox do to my bike? How does it operate? How many gears do I have? Total Newbie questions I know, search and youtube didnt yield much info.
Click to expand...
The only way to install gears on your 66 CC 2 stroke is to add a Sick Bike Parts shift kit or make a home made version.
The 49 and 66 CC bicycle motors, KTM and Morinis have built in gears on the clutch side which gives a ~4 to 1 gearing reduction.
Most of the 4 stroke and 2 stroke utility motors we use have no built in reduction so the output shaft spins at full motor rpm.
These motors need a transmission or "gearbox" which is really just a Jack shaft set up that is a single ratio with no ability to change gears.

However there are a few dual range gearboxes like msrfan has recently started using on his 5 HP Briggs race bike.
Also CVC transmissions use expanding pulleys and belts to automatically change gear ratios.
 
Last edited:
mew905

mew905

New Member
Sep 24, 2012
647
9
0
Moose Jaw
knightscape said:
Please forgive what may be a stupid question about jackshafts, I've been searching and not finding what I'm looking for... The bike I'm looking to set up with the kit I'm tinkering on is a rear-deraileur geared bike with disc brake and a single front chainring. I'd like to get a jackshaft set up going to take advantage of the gears and lose the scary stock tensioner and ragjoint to allow the disc brake. Here's the question: Is it possible to set up a jackshaft such that when you are actively pedaling without the motor running, you are not turning the engine's drive chain? From what I've been reading, the answer seems like a "no", is that right? You need to be turning the drive chain (via pedaling) to start the engine? If so, is there an alternate way to do what I'm looking for? I'd like the ability to pedal without any added friction in the drivetrain, but then when I want to motor, to engage the engine and let 'er rip. Motor is a 2-stroke of unknown (49-66?) cc's. Also, perhaps I've got something out of whack with my set up, cause I am new to this, but I can definitely feel the added drag when I am pedaling with the clutch disengaged, it's not a ton, but its there. I'm looking to be able to completely ride the bike like normal, but then crank up the engine for quickly covering ground. Am I making any sense?
Click to expand...
No, unless you have a pin like the hybriped system, you crank your pedals, you crank the motor, the least resistance you will ever have is the leeching of the motor with the clutch disengaged. However at a point it seemed like you wanted a way to start the motor with the jackshaft kit without having to pedal. The nature of the bicycle tire is when you're moving the chain wont spin so you can glide along. However this means you cant use your momentum to start the motor. The jackshaft uses another freewheel on the pedals so when the motor is turning the crank, and thus the chain, again you can glide. Here's the fun part:

Because the normal casettes utilize a system so you dont have to pedal all the time, you have a redundant freewheel in the pedals. So, to use your momentum and start the motor the same way you did with the rag joint, you need a "fixie" (fixed gear hub). This means that no matter what, your wheel will turn your pedals, but because your pedals have a freewheel too, it cant, so it just turns the motor. You can get fixie geared hubs, for relatively decent prices (~$140). No derailleur, no tensioner needed, instant gear changes, momentum starts, and pedals still glide. Win all-round :)
 
knightscape

knightscape

Member
Jul 29, 2013
340
1
16
Maine
mew905 said:
instant gear changes
Click to expand...
That had me all confused till I remembered Sturmey Archer started making the ridiculously named S3X hub, I had completely forgotten that was a thing. I'm very familiar with fixed gear bikes. Fixed gears on road and single speed mountain bikes been my preferred mode of riding for the last decade. Using that hub with a jack shaft would be almost perfect. I just wish they made a disc brake model of it on a 135mm OLD spacing.
 
You must log in or register to reply here.
Top Bottom