jackshaft crankcase

[jj256]

how do you put a jackshaft inside a crackcase or bottom bracket?

 

[expjawa]

I think you might have to explain what you mean. I can't think of how the term "jack shaft" relates to a bicycle at all. In a number of other applications, sure, but not to a bike...

 

[jj256]

On board track racers, some bikes have a jackshaft in the bottom bracket

 

[junknutz1975]

im stumped...
can you post a pic of what you mean?

 

[c.p.odom]

Jackshaft is more of a slang term for a countershaft. What he wants to do is to replace the crank with a spindle that supports two chainrings that will synchronize the engine to the rear wheel.

 

[expjawa]

In my line of work, the term "jackshaft" is often used to mean an intermediate shaft. Something that might be used to connect, say, a differential to an axle shaft. You see this a lot on FWD cars that have equal length CV joint shafts. Still not entirely clear how this relates to a bike. I do (now) have the impression that this relates to a motorized bike, which is not information that the original poster included in his posts.

 

[wheelbender6]

I have seen jackshafts used on long, stretch bicycles. The chain is generally tighter and doesn't fall off as much when the jackshaft is used. Other than that, I have only seen them on bikes with engines or electric motors. Sickbikeparts,com sells jackshaft kits, but they are intended for use with China girl motors.

 

[jj256]

nawl that aint going to work, I gotta a big boy hood motor, my question is how do you put a jackshaft in a bottom bracket

 

[jj256]

can any one please tell me how to put a jackshaft in a bottom bracket, like Cleatus_Fathom's bike

 

[dracothered]

nawl that aint going to work, I gotta a big boy hood motor, my question is how do you put a jackshaft in a bottom bracket

You have to install a free wheel bearing on your pedal chain ring so you can use the shaft as a jack shaft also. Hope that helps you somewhat.

 

[jj256]

ok can i do that with regular bearings or snap bearings only

 

[cave12man]

I honestly have no idea what you guys are talking about, BUT, apparently somewhere in this thread on motorbicycling.com there's some info on how to do a jackshaft/pedal combo. I did a search for Cleatus_Fathom because I was dying to know what the heck a jackshaft was, and in one of his threads someone posted this for him:

http://motorbicycling.com/showthread.php?t=28747

Hope it helps.

 

[dracothered]

I honestly have no idea what you guys are talking about, BUT, apparently somewhere in this thread on motorbicycling.com there's some info on how to do a jackshaft/pedal combo. I did a search for Cleatus_Fathom because I was dying to know what the heck a jackshaft was, and in one of his threads someone posted this for him:

http://motorbicycling.com/showthread.php?t=28747

Hope it helps.

Here is where it shows how it was done.

http://motorbicycling.com/showpost.php?p=311592&postcount=26
http://motorbicycling.com/showpost.php?p=315020&postcount=35

 

[frameteam2003]

Crank on that motor and those pedal crank arms are sure going to spin!

 

[frameteam2003]

Oh and all he did was knock in two large press fit barrings

 

[frameteam2003]

OK his drawing shows how it works---the jack-shaft is hollow for the pedal spindel to go through.Seems it would be a lot simpler to have put a bearing on the motor-sprockets and pushed it onto the crank spindel.

 

[jj256]

Got a another question I was looking at the jackshaft kits on mfg supply, and I was looking at the bearings and bearing hangers. So can I take a regular sealed bearing, a heavy duty washer, and some snap rings and build my jackshaft. Will the snap rings keep the bearings in place?

 

[jj256]

I.just came up with a idea. What if I were to take a old bike hub put some sealed bearings in it.and use a grade 8 bolt for the shaft.

 

[dracothered]

I.just came up with a idea. What if I were to take a old bike hub put some sealed bearings in it.and use a grade 8 bolt for the shaft.

A keyed shaft doesn't cost much and it is made for what you want to do more than a bolt. Bolts are made for pressure put on them in a pulling direction not a twisting direction.

IE: When a bolt is tightened down the bolt gets stretched a little length wise. This is where they have their strength.

 

[jj256]

OK so get a shaft sounds like a plan