Is there a way to make a 2 speed without having to buy the jackshaft kit?

[Steve Best]

Simple possibility is 4 pulleys and 2 belts. Tighten one belt and loosen the other to effect a shift.
Still needs a jackshaft but would work especially well with a motor without a clutch.

 

[Frankenstein]

When you mean shaftless, do you just mean you don't want to swap over to the other side, or you mean you want nothing to do with bearings or gears on a shaft?

What kind of equipment are you hoping to use to build this? What are the size requirements? I have an idea or 2 but I don't know if you want a box hanging off the side of your bike, unless you can settle with routing chains into, say, a 50 caliber ammo cannister.

I mean if you want to do this may as well make it extremely unique, cool looking, and capable of protecting some main components of your to be transmission, your asking for something not particularly easy to do effectively just as is.

Please more info

 

[BikeBuilder43]

We all know when you bump start these bikes the top chain has a sudden loss of tension as the rear sprocket is pulling the bottom chain to crank the motor. We need to eliminate that slack and fab up some kind of derailleur system since we are only using 2 sprockets. The tensioner doesn't have to have much tension as it is only keeping enough tension on the upper chain during starting to not come off the sprockets.

 

[BikeBuilder43]

I m trying to come up with a cheap alternative to the jackshaft kit. It is a bit pricey and a p.i.t.a. to get right. I know that having at least 2 gears would make a world of difference. We may have to use chain from a freestyle bmx. It isn't as thick as the kit chain but still thicker than mountain bike chains.

 

[Street Ryderz]

I m trying to come up with a cheap alternative to the jackshaft kit. It is a bit pricey and a p.i.t.a. to get right. I know that having at least 2 gears would make a world of difference. We may have to use chain from a freestyle bmx. It isn't as thick as the kit chain but still thicker than mountain bike chains.

For what frame?

 

[FurryOnTheInside]

I'll add to Street's question... Can we see some pictures of your current setup that you want to add/change to a two speed system? I checked your profile but there's no media page there.
Physical space constraints could be the limiting factor.

Do you have a stand that allows you to pedal the bike (by hand if not by sitting on it and pedalling) so you can test and see chain movement and stuff?

Slack in the upper run if chain during bump start - if you're in low gear there is little slack anywhere and that little bit should be able to be controlled. It also only happens when you start the engine, and most people only start it once, not multiple times during a ride, so setup can be specifically for the start-up and then changed to running and gear changing setup.
It's the engine braking during high gear deceleration and downhills that is the big slack issue IMO.
So what's been the biggest change in derailleur technology in the last decade, apart from Di-2?

I have the #410 bmx chain already and I'm sure it is perfectly fine for single speed use as many others are using it. I wouldn't expect it to fit through any derailleurs though or be the best thing for that. IMO.
The 11t drive sprocket reduces chain load by about 10% ...according to my logic at least.
Of course you can tell I'm thinking only of a derailleur based system, myself; but the options brought up by Timbone, Steve Best and Frankenstein are interesting too!

 

[BikeBuilder43]

I sold my old setup. It was a cruiser frame with a 32 tooth out back. I know there is very little slack on the top chain in a normal setup. I am thinking if I bolted 2 sprockets of different sizes together on the motor chain side where they normally go. When using the smaller sprocket there would be that slack to contend with.

 

[FurryOnTheInside]

I sold my old setup. It was a cruiser frame with a 32 tooth out back. I know there is very little slack on the top chain in a normal setup. I am thinking if I bolted 2 sprockets of different sizes together on the motor chain side where they normally go. When using the smaller sprocket there would be that slack to contend with.

Yes, I agree that excess chain take-up and control in high gear is the issue.

There has to be enough slack in low gear to get the chain over the teeth and onto the larger sprocket, so there will be a little more slack in low gear than there is on a single speed setup, but not much.

Look at downhill/freeride and enduro bikes with long travel rear suspension. They have lots of slack appearing very suddenly in all gears when the suspension is compressed. How do they deal with it? Both in the past and more recent developments. What components are available for cheap that we can use to try to build something that works for us?

 

[BikeBuilder43]

Maybe we can have SOME slack if we use a chain guide. Then there can be slack when bump starting and when the throttle is let off.

 

[Steve Best]

You do need a slight amount of slack in the chain or you will do physical damage to chain, bearings and axles.
A spring tensioner will work but adds driveline slop and unless very light adds drag. It needs travel stops too.
Using your guard idea, many applications use slide tensioners but they typically add considerable drag.
Examples are camshaft sliders (bathed in oil) and MX bike swingarm sliders.
I do have 2 idler (tension) sprockets on one of my bikes that I used for higher speed riding.

I was getting a harmonic where the top chain vibrated terribly while coasting at speed.

The best direct chain setup would be:
1) Largest front sprocket your gear ratio can afford to minimize chain wear
2) perfect alignment of front, rear and idler sprockets
3) Perfect concentricy and runout of all sprockets
4) straight ( or straightest possible) chain runs for between 2 sprockets, ie; tensioned with sprocket distance
5) Slight slack or lightest tension tension possible on the chain for minimal drag.
6) Idlers or sliders barely touching the chain may be needed on straight chain runs to eliminate harmonics.
7) Light, non-throw, creeping high pressure lubricants and ideally a cover to prevent loss and dirt intrusion.
8) minimal chain angles when tensioners are required to reduce wear and friction.
9) dual bearing tensioner idlers to reduce binding bearing race friction.