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Anyone Running Power THRU the Bottom Bracket?


Well-Known Member
Jun 22, 2007
Or build our own left hand lower drive...

The Left side of the pedal crank set...

Then too a reversed internal left hand rear gear set...
Of course we would need to rely on our machine shop person to build this for us... Ha 😁
View attachment 97771

Part of the trick is too use a 140,,, 160,,, or 200mm fat tire bike frame...

Use a narrower hub so we can add a left hand side engine drive sproket,,, or add a thinner right hand side cassette too gain more room for the engine drive side...

No Jack-shaft kit needed,,, the engine is easy to swap out since there is no Jack-shaft brakets in the way """if"" we need too swap out engines,,, and the pedal bike chain and gears remain untouched...

We will put a wider crank set stem on,,, a large floating bearing so the 2 sprokets turn by engine power on Left side...
1 sproket the driven,,, the other will be the drive that will feed power to rear hub...

Yes,,, thinking out side the box,,, at least there wont be no Jack-shaft kit ...
And we get to run the heavy duty drive chain 👍

Still designing Don

When the rear tire is going around,,, both chains to sprokets will be spinning,,, let clutch out and Zoom Zoom...

We will find out if our machinest can add a nutral in the rear internal gear hub...
That way we can pedal the bike with no engine drive chain drag...

The drawing is a 2+ 2 gear set for the engine power side...
I’m revisiting posts in this thread to respond to:

Don, if I’m reading you correctly, you do not need a machinist to create this idea of yours.

You can do it!!

Are you eliminating the jack shaft and trying to connect the engine to the bottom bracket?

It’s been done before. In fact, Sportsman Flyer has this option.

Also, I’m helping a fellow member create the same setup I think you’re trying to.

Basically, the engine clutch drives a chain to a large chainring idler sprocket.
This sprocket is bolted to another chainring sprocket.

Both of these chainrings are on the left side of the spindle.

Then that chainring is chained to the rear wheel sprocket.

Using a large 4-stroke engine allows you to create a gear ratio low enough to power the bike.

It’d be very difficult to gear a 2-stroke engine, low enough to optimize its potential.

Thankfully, it’s easier for Crimson Prince, the member I’m helping.

He’s using a pocket bike engine with a tiny 6-tooth clutch sprocket and a 54t chainring sprocket.

Since this sprocket has 8mm pitch, the 54t chainring is less than 5.5” diameter.

That’s the size of a 34t bike sprocket.

So, the engine connects to the 54t.
Then, this sprocket bolts onto a smaller chainring sprocket.
This is then chained to the rear wheel sprocket.

But won’t the pedals spin, when the engine drives the chainring sprockets?


The secret to its success is that the chainring sprockets run on IDLER BEARINGS!

This means that both sprockets won't spin, when the pedals and their spindle spin.

They have bearings which allow them to spin, independently of the shaft.

In fact, the chainring drive sprocket can “float” around the bottom bracket spindle.

That’s because the 54t driven sprocket is literally supporting the 25t drive sprocket in midair!

From there, it’s a chain to the rear wheel sprocket.

Seems simple, right?
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