Bottom Bracket Jackshaft With Pedals?

I admire NLbike's rat rod. It has a pocket bike engine mounted mid-frame. Power is chain-driven through the bike's bottom bracket (BB) on the left-side. The chain ring sprocket on the right side of the BB connects power to the rear sprocket.

Here I go again. I have a bare Diamondback cruiser-type frame that had never been built. I gain inspiration from NLbike's creation. However, his bike has no pedals; I need pedals.

I can envision a flat plate or generic 4-stroke motor mount on my bike frame. It's bolted or welded to the frame tubes and a Tanaka 3hp 47R or 4.5hp GP460 engine. The engine will have a 6-tooth bell housing sprocket on its left-side. There is no 5:1 gearbox, which would make the engine wider. The 6-tooth drives a T8F pocket bike chain to a 36-tooth sprocket, which is bolted onto an extended BB axle, inboard of the left foot pedal crank arm.

This is the extended axle for the BB:

http://custommotoredbicycles.com/wi...r_clearing_4_stroke_motors68mm_bottom_bracket


The 36t sprocket will have no freewheel; the 6t on the bell housing freewheels at idle speed. On the right side of the BB, a 22-tooth BMX sprocket bolts onto the BB axle, inboard of the right foot pedal crank arm. The chain runs back to an 8-speed internal hub with a 25t sprocket, which is dished to clear the 1/2" x 1/8" chain. With the correct sprocket combination, 8th gear(1st gear) is a stump-pulling 48.75:1. Final drive is 13.64:1.

How do I stop the pedals from spinning? Methinks it's a simple solution, but I just can't figure it out right now.

Thanks for help.

Sorry, that's not it.

I believe the solution MIGHT be coming to me.....slowwwwwly.

I have an SBP shift kit on my other bike. The only thing I can utilize from SBP are both pedal crank arms and the right-hand (RH)freewheel.

Both axle/jackshaft sprockets do not need freewheels. It's unnecessary, because of the freewheel on the rear axle and the freewheeling (sort of) engine sprocket.

Eureka! BOTH pedal crank arms need freewheels!!! Not the jackshaft sprockets!!!

When the engine powers the BB axle/jackshaft, it will spin. With the back wheel off the ground, you'll be able to see the BB axle/jackshaft SPINNING inside the ends of both pedal crank arms! This is while both foot pedals are standing still or being pedaled.

To make it easier, trial fit the jackshaft/bottom bracket (BB) outside of the bike frame. I haven't done it yet; I can see this jackshaft being assembled in my head.

Okayyy, the first thing to do is drill out the square ends of both pedal crank arms, about 3/4". This will allow the BB axle to spin, without turning the foot pedals! You'll be watching the square ends of the 5/8" inside diameter BB/jackshaft spinning INSIDE the round end of the pedal crank arms. Remember, you drilled out the square end of the pedalcrank arms into a 3/4" round hole.

Screw the RH freewheel onto the right pedal crank arm, as usual. Set this aside.

Buy two of these:
http://www.staton-inc.com/store/index.php?p=product&id=529

Screw one onto this BMX sprocket:http://www.staton-inc.com/store/index.php?p=product&id=2257

Choose a solid sprocket which will not need a freewheel.

Slide the BMX sprocket onto the 5/8" axle. Snug fit. You will align it perfectly with the rear wheel sprocket later, when you install the bicycle chain.

Slide the adaptor with the RH freewheel onto the BB axle. Line up the freewheel holes with the freewheel on the pedal crank arm. Bolt them together. You'll need to ensure that the axle has keyways grooved on both sides of the bottom bracket (BB).

Okay, the easy part's done. On to the left-side of the BB.

Try to buy a sprocket which slides directly onto the 5/8" BB axle, not needing a freewheel. If you can't find one, use the second adaptor onto the 36-tooth(36t) sprocket. I'll be using T8F chain and sprockets from engine to jackshaft/BB axle. (Chain links are closer, making for smaller-diameter sprockets and lower gearing(higher numerically). Slide the 36t onto the axle and secure snugly with keyway/set screws/collars.

Now order one of these:
http://www.staton-inc.com/store/index.php?p=product&id=2170

and two of these:
http://www.staton-inc.com/store/index.php?p=product&id=967

Screw one left-hand (LH) freewheel onto the left-hand adaptor. Slide this onto the BB axle and snug fit, towards the center.

Now comes the machining part. Take both SBP pedal crank arms and the freewheel with LH threads to the machine shop. The right-side crank arm is for the machinist's FYI/show- and-tell. Ask the machinist to cut the left-side pedal crank arm to fit the LH freewheel. I believe it's 1.375x24tpi (threads per inch). Install the LH freewheel while at the shop.

When you get home, slip the left-side crank pedal arm onto the BB axle. Line up the holes with the inboard LH freewheel and bolt it together. Snug all the parts and spin that BB axle!

Disassemble the sprockets and adaptors. Reassemble the BB axle into the bottom bracket and voila!

It'll work like a charm. I know it will. I can see it in my head!

I'm buying parts tonight!

I'll take pictures when I buy the parts, assemble this BB/jackshaft and learn how to use my I-phone.

Tony01 said:

Gearing issues make a separate pedal chain more reasonable. Better to float the jackshaft reduction on the pedal crank like the sportsman flyers.

Click to expand...

Tony, it's simple gearing:

72t rear sprocket, 12t chain ring = 6:1
9t engine sprocket, 27t left-side jackshaft = 3:1
6 x 3 =18:1 gearing.

With 8-speed hub's 3.25 low, use 25t rear sprocket and 10t chain ring.
3.25 x (25/10) = 8.125.
6t engine sprocket, 36t left-side jackshaft = 6:1.
8.125 x 6 = 48.75:1
1.00 high x (25/10) x 6 = 15:1 final drive

You don't need that second jackshaft if you use T8F or even #25 sprockets.

Agreen said:

Yeah, I must have misunderstood at first. While I agree that you would need freewheels for both crank arms, think of the consequences. Your crank arms will do all kinds of craziness. In other words, they won't stay in synch and you'll end up with saddle stirrups.

Click to expand...

Agreen, you might be right.

Okay, at this point, I have an effective jackshaft with an elaborate set of fake pedals.

Back to the drawing board.

Irish, I might need this:
http://sickbikeparts.com/4-stroke-shift-kit/

I was hoping to do without.

Agreen said:

Yeah, I must have misunderstood at first. While I agree that you would need freewheels for both crank arms, think of the consequences. Your crank arms will do all kinds of craziness. In other words, they won't stay in synch and you'll end up with saddle stirrups.

Click to expand...

Well well well!!

Take a look at THIS website:http://www.powercranks.com/OrderPowerCranks.html

My bottom bracket/jackshaft experiment might still be possible! The video on this website did look like crazy crank arms. However, there seems to be a purpose and a method to their madness.

Granted, these power arms cost $1K and look high-tech. What I proposed may cost $100 if using cheaper freewheels to trial-test it.

I feel hopeful. I have most of the parts laying around to assemble the BB/jackshaft. It's worth a try.

To be continued.....

Well, the sprockets, adaptors and left-hand freewheels to create the bottom bracket jackshaft arrived. I need to groove the left-side BB for a keyway and have left-hand threads cut onto the pedal crank arm.

I couldn't find anyone to groove the 8" bottom bracket cartridge I'd intended to use. I needed that to be done, so the freewheeling sprocket on the left-side wouldn't slip on the round shaft. Besides, I don't like to rely on set screws to secure anything on the spinning shaft.

Soo, I decided to create a new bottom bracket (BB) from scratch. I'll be using two 499502HNR bearings, a 12" grooved 5/8" shaft and two locking collars. The bearings have snap ring retainers. The locking collars should keep the BB solid.

I'll trim the 5/8" shaft to fit, when I'm finished.

Pictures later, when I get it done.

I give up.

No more bottom bracket (BB) jackshaft with pedals.
In fact, no jackshaft needed at all.

After riding my Scooterguy-mounted Tanaka 47R motorized bike yesterday I had an epiphany. At times, I had to maneuver the bike at crawling speed along uneven sidewalks.

That's when the bike pedals came in very handy.

It is time for a major correction in midstream. On my new midframe build, I NEED working pedals.

I'll turn the engine around 180 degrees on the motor mounting plate. This moves the drive/driven pulleys from the left side of the bike to the right side. Now ALL chains and sprockets will be on the right side. Of course, the engine needs reverse-rotation. Using a 5:1 pocketbike tranny will now drive ALL sprockets clockwise and spin the rear wheel.

The BB technically becomes the jackshaft on the right side only, ala shift kit.

If there's any consolation, now my new chrome exhaust system from an X1 pocket bike fits PERFECTLY.....

when installed upside-down.

Namaste, friend. Yes, now I realize the importance of using pedals.