Bottom Bracket Question

Ok, I am in the process of building a custom bottom bracket for a custom build I am working on but need some help with something. I am looking at using a 3/4" ID x 1 5/8" outside diameter bearing and going to be putting a 3/4" shaft as my spindle. I'm wanting to press fit this bearing into tubing but have seen some 4130 chromoly tubing with an inside diameter of 1.624 but the company cannot guarantee or even knows if that really is the ID of the tubing. So, my question is, has anyone used this size bearing and pressed fit it into this size tubing before? Or, maybe someone can give me some ideas for making a custom bottom bracket they might have seen using a 3/4" ID bearing? Reason for making a custom BB is because all the ones I have seen don't give me the ability to move the drive sprocket on the cranks out far enough to clear the engine I will be using.

More info on the build I have going. I am making a bike from the ground up..Frame and all...using a Lifan Engine (biggest I will go is 125 but probably going to do a 90cc). Will be using the idea of the jackshaft from that of the motoped.com setup but the bike is going to be more of a chopper style/cafe racer style bike. I just got my rims and tires build (They are Maxxis Hookworms with Halo SAS 36spoke rims..a Halo spin doctor front hub and a custom built rear hub from Phil Woods (double iso on both sides: for disk and for sprocket) )...will try and post pics soon but need to get this bottom bracket situated and the jackshaft..once that is done I am off to the races on getting the frame situated..

So, if anyone can give me some idea on this bottom bracket I would greatly appreciate it. I would have just tried to buy the one from motopeds so I don't have to build one but those guys never respond back to my request on stuff like that so I'm guessing they don't want to give that info up. I could machine a solid piece to accommodate the bearing but I feel like there is a tubing that has a thick enough wall that I can press fit these bearing without having to re-create the wheel on this but just going blank on where to find it. Thanks in advance to anyone who got this far in my post and can give me some help.

 

[IbedaYank]

maching one would be the better option as then you can put in steps for the bearing to sit against no need for spacers on the shaft

 

[Pablo]

Tubing ID varies too much to expect a proper press fit, just chuck it up in the lathe.

I am curious about this:

Reason for making a custom BB is because all the ones I have seen don't give me the ability to move the drive sprocket on the cranks out far enough to clear the engine I will be using.

How far from the outer bearing face are you talking?

 

[vegas3416]

I might have said that part wrong but if you look at the motoped.com bike you'll see how the bottom bracket looks.. that's basically the idea for what I'm doing. but as far as the distance away the bearing face.. I'm looking to keep it as close as possible but just haven't found a setup that is currently made that is wide enough. I want to run the chain system almost identical to the motoped bike but if I try to run the chain from the pedals to the jackshaft closer to the frame I will have to run a crazy chain either over the engine or under requiring multiple chain tensioner pulleys but I might be thinking about it wrong as well.

 

[Pablo]

I might have said that part wrong but if you look at the motoped.com bike you'll see how the bottom bracket looks.. that's basically the idea for what I'm doing. but as far as the distance away the bearing face.. I'm looking to keep it as close as possible but just haven't found a setup that is currently made that is wide enough. I want to run the chain system almost identical to the motoped bike but if I try to run the chain from the pedals to the jackshaft closer to the frame I will have to run a crazy chain either over the engine or under requiring multiple chain tensioner pulleys but I might be thinking about it wrong as well.

motoped.com is nothing that I can find??? Is that the correct name?

 

[vegas3416]

sorry www.motopeds.com Forgot the "s"

 

[Pablo]

Neato.

Have you looked at the 206mm bottom bracket cartridge?

 

[vegas3416]

Yeah but the issue is not necessarily the pedal cranks its the sprocket and chain issue...using that setup the sprocket is right up against the BB which is fine if I didn't have to put the engine so low..because doing it with a 206 BB cartridge I have to run about 4 chain idler pulleys to re-route the chain either over the engine or underneath the frame..can be done but just rather do similar to the setup that motopeds has because i can put the engine a little further forward and not have to worry about chain routing as much, but then again the frame build is still in process and I don't really have any exact ideas (just ideas lol) on what I want to do. All I know is I am doing this build and won't rest until I finish it.

 

[V 35]

How about shafting [ steel rod, ground true ] for the Pedal Crankshaft ? That would slide through bearings more accurately than tubing would.
You could mill the ends of the shafting to accept pedal crank arms. Sounds like a real gonzo build, I'd consider cutting up a few cheapo bikes, and play with the parts, before spending big bucks at the machine shop. Since the pedal crank is low rpm, you could use two cartridges, end to end, coupled with an adapter made from chopped crank arms . If you can afford it, you can have it.

I admire your ambition, to build a real ' high ender ' Being a tough, practical, yankee ... I believe in adapting existing technology, and machined parts, to your unique application. Good luck .

 

[vegas3416]

This is something I have been wanting to do for a while and since I can write it off..I'm going a little crazy but need to make it look good.