Anyone Running Power THRU the Bottom Bracket?

[5-7HEAVEN]

Has anyone used their bottom bracket to send engine power to the other side of the bicycle?

I just woke up with this bright idea!
It's not even on paper yet.

Doing so would clean up the right side of the bicycle. All the engine's sprockets and chains/belts would be grouped tightly on the left side of the bike.

In fact, the original chain guard, three custom chainring sprockets AND front derailleur could be left in place on the right side.

Of course, most of you who are familiar with motorizing bikes would scoff and mention that the final gear ratio(s) would be ridiculously too high(low numerically).

Throughout the years, I imagine that several MBer's have simply chopped off the pedals, chained their engine to the sprocket on the bottom bracket and Voila!

Motorized bike!

Of course, low gear ratios for high-winding 2-stroke engines wouldn't be easy to set up.
However, proper gearing for big 4-stroke might be possible, ESPECIALLY if no pedals are used.
Having working pedals while running engine power THRU the BB makes for an EXTREMELY difficult build!

Let me run this past you fellow MBers, and how I'd think of gearing my 212 engine build:

The key to my project's gearing is using timing belts and pulleys. It allows me to use a 44-tooth gear that's 2.75" diameter(44t chain sprocket is 7" diameter).
My 83t pulley is 8.3"(83t sprocket is over 13" diameter!).

 

[5-7HEAVEN]

The next item of importance is the jackshaft. It is 4" long and located under the motor plate, to the front of the engine. The big difference is that the pulleys on this short shaft are placed side-by-side.
The pulleys are grouped tightly around the clutch.There's less than 3" between the edges of the 44t jackshaft pulley and the 23t clutch drum. A 5mm belt connects them to each other
Placed right next to the 44t is the 17t jackshaft pulley. An 8mm belt links it to the 83t chainring pulley.

The distance between the edge of the clutch drum and the 83t pulley on the BB is 3".
The gear ratio, as it transfer power thru the BB, is (44/23) x (83/17 = 9.34:1.
It's common knowledge that there is no keyway on the left side of the BB shaft. A fella could have the shaft cut for the key, or rely on two set screws to sevure the 83t pulley to the BB.
Setscrews could possibly secure the driven sprocket on the BB. However, the pedals would spin like crazy, since they're bolted onto the BB shaft!

 

[Captain Rainmaker]

The jackshaft kit from Sick Bike Parts basically does this. The engine's power is routed through a jackshaft which takes it to the left side, where it spins a freewheeling chainring that drives the rear wheel through the existing rear derailleur. This allows you to change gear ratios for the engine, and since the chainring is on a freewheel, the pedals remain functional.


It does necessitate the removal of the front derailleur, but if your bike is motorized, it's probably fine without it.

 

[5-7HEAVEN]

I WAS gonna design my jackshaft the SBP way, but came up with this option.

The bottom bracket(BB) IS the jackshaft. There is no other jackshaft transferring power to the other side.

I'm relaying the information thru several posts, as it develops in my brain.

 

[Captain Rainmaker]

I WAS gonna design my jackshaft that way, but came up with this option.

The bottom bracket(BB) IS the jackshaft. There is no other jackshaft transferring power to the other side.

I'm relaying the information thru several posts, as it develops in my brain.

So would you be deleting the pedals entirely then? I can't think of a way to send power through the bottom bracket without spinning the pedals as well, unless you engineer something crazy like a bottom bracket with two concentric shafts.

Not to discourage you or anything, but I'm having trouble seeing where this is going. Seems to me like it's just reinventing the wheel.

 

[CrazyDan]

You could always go with my idea and weld a second bottom bracket in and keep your pedals.

 

[5-7HEAVEN]

My intent is to simply this jigsaw puzzle of sprockets and chains/ belts and pulleys. I'm trying to group all the motorized components tightly around the engine clutch.

 

[5-7HEAVEN]

The next step is to replace my BB cartridge with an old-fashioned 3-piece bottom bracket. It has a shaft, cups and ball bearings.

The reason for repkacing the BB is to have that 5/8" shaft. My BB cartridge is 8.75" wide, so an 8" shaft works.

The most important feature is that the new shaft is grooved from end to end.

You'll appreciate its importance when the pedals are modified to fully operate.

 

[5-7HEAVEN]

So would you be deleting the pedals entirely then? I can't think of a way to send power through the bottom bracket without spinning the pedals as well, unless you engineer something crazy like a bottom bracket with two concentric shafts.

Not to discourage you or anything, but I'm having trouble seeing where this is going. Seems to me like it's just reinventing the wheel.

When I"m done with this presentation, you'll realize this idea is unique!

It is VERY complicated. I'd guess that 99.999% of MBers would not be interested in building their bike this way.

Yes, pedals will be fully operational.

 

[5-7HEAVEN]

After the new BB shaft is installed, the 83t can be installed with a key.
Now the 24t chainring sprocket can be bolted.on the other side of the bike, with no freewheel.
In fact, 2 more chainrings can be installed. If you match the 3 sprockets' DISTANCES with the original ones, the original front derailleur can be reinstalled