Threadless BB fit

[Conrad_K]

I bought a bottom bracket cartridge for a bike project. It's a 68mm threadless type intended for use in frames with stripped threads. I'll be making my own housing on my lathe.

Question: what is the fit supposed to be, between the threadless BB and the threaded housing? It can't be a press fit, at least on the screw-in side, or you wouldn't be able to screw it together.

 

[wafter]

Not familiar with threadless but I assume it's just a plain shank with a thread and collar on one end that clamps it into the BB shell...?

Can't quote fits (and I think you'll struggle to get any meaningful values) however common sense would suggest measuring the OD of the BB housing and cutting the bore of the shell to give a very light press-fit or sliding fit based on standard limits and fits.. you probably wouldn't want it sloppy and a very light press-fit wouldn't be difficult to remove if well lubed before fitment.

 

[Cycleops]

Don't really get you @Conrad_K . So what are you using the threadless BB on? A threaded BB? You say you'll make your own housing.What is it going into and how will you secure it?
Is the frame aluminium, carbon or steel?

 

[cyberknight]

the only BB i have come across for knackered threads screws into itself and doesn't need a housing custom built , it would be interesting to see links and pictures of what you intend to do .

 

[midlife]

Both sides of the threadless BB clamp onto the outsides of the BB shell by way of the two sides tightening against each other. Fire and forget.

There was a deliberate threadiess system from my day which needed a special chamfer on the BB, Mavic I think but won’t be one of them.

 

[fossyant]

There are systems that use a tube in the middle that each bearing screws into, if that's what you mean, where the frame has damaged threads, or replacing pressfit.

 

[wafter]

Both sides of the threadless BB clamp onto the outsides of the BB shell by way of the two sides tightening against each other. Fire and forget.

There was a deliberate threadiess system from my day which needed a special chamfer on the BB, Mavic I think but won’t be one of them.

Indeed - I googled it and what you describe fits perfectly, and makes sense.... like this:

 

[Gunk]

Indeed - I googled it and what you describe fits perfectly, and makes sense.... like this:

View attachment 734191

I used one a few years in a frame with chewed up BB threads, worked a treat.

 

[Conrad_K]

Indeed - I googled it and what you describe fits perfectly, and makes sense.... like this:

View attachment 734191

That is exactly it; same part number even.

I'll be making the housing out of steel.

The usual .001 or so press fit would probably work fine for the fixed end, but the threaded end has to turn inside the housing, so it would ordinarily have some clearance. The inner edge of the nut/sleeve/thing has a 45 degree taper and a rubber gasket, which doesn't really look like enough to keep it from moving around.

I had thought this morning; it wouldn't be much more work to slot the housing and weld on some brackets for pinch bolts. That would take all the guesswork out of clearances.

 

[midlife]

I'm confused..... What housing?

Just screw it together either side of the BB shell. , BITD we would do it up as tight as we could as torque wrenches were for car cylinder heads lol.

 

[Cycleops]

I'm also confused so perhaps he could explain. Sounds like might be making a frame?

 

[biggs682]

I think the op is making there own bottom bracket shell

 

[Conrad_K]

I have an elderly "compact long wheelbase" recumbent. It came with a 20 inch rear wheel, a 48-tooth single chainring in front, and a 7-speed cassette in back. The cogs run from 13 to 26.

Pedaling as fast as I can, elderly ladies up uprights pass me with little effort. On the flip side, there are a number of hills in my area that I can just barely negotiate without having to get off and push. Going up is a lot of No Fun.

After evaluating several ways to deal with the problem, I decided to add an intermediate gearset. Flip the 48-tooth chainset up front around to drive on the left, then fabricate a housing for a 68mm BB to take a standard 48-38-28 triple chainring on each side, with a post for the derailleur.

48 teeth up front and 13-26 in back looks pretty normal for 26" uprights. If I remove the 48 and 28 tooth chainrings from the left side, the speed step-up from 48 in front to 38 teeth is within a few percent of what I'd get if I could fit a 26" tire, if I use the 38-tooth center chainring on the right so the ratio is 1:1. Which would make the hill problem even worse, except I could now drop into "low range" with the 28-tooth chainring. I probably don't need the 48-tooth ring given the step-up, but I'll see if I have any use for it before I remove it.

The bike has a 1.5" square tube frame. The BB housing is welded in, but the seat slides forward and back with a yoke and pinch bolts. I'm making a sliding bracket like that to weld the new housing to; it will ride just in front of the seat yoke. I would just weld it to the seat yoke, except I usually remove the seat when transporting the bike, and that would be awkward with chains and a derailleur cable.

Yes, all that adds weight, complexity, and power loss. It's an exercise bike, and it already weighs 40+ pounds. A few extra pounds isn't a deal-breaker.

 

[Ajax Bay]

What a project! Currently you have a gear range of 38" - 76" *
If you 'actually' have 7sp cassette on the back (it'll probably be a freewheel nd block) then perhaps going to a 12-32t cassette would give you a greater range (for the senior lady racing and the hills 'in your area'): 27"-80".
https://www.teamcycles.com/componen...-hg200-alivio-7-speed-cassette-12-32t__12001?
* As an aside, the British method of describing gearing by inches comes into its own in this sort of discussion.