Raleigh 20 BB
 

I thought about the Raleigh 20 BB

People dont want to modify the frame

So youve got to use the standard BB. With cottered cranks.
Or get a difficult to obtain BB and a set of expensive BB cups.

I thought there must be a better way.

So I looked in my box of axles.
Theres a cartridge from a bike that had plastic BB cups on both sides.
Id butchered the BB cups to get the cartridge out.
This is a good fit in the standard BB cups.

I cleaned the BB shell and the cups
Screwed the left cup in all the way, to clear the paint from the threads.
Then test fitted the BB
Seems to be fine.

I tried cranks on it.
Had to select ones that are shallow on the axle.
So older cheap ones wont fit:(
But these ones are ok.

http://i29.photobucket.com/albums/c2...cw35/R20bb.jpg

Dont know if the cups will stay put. Might loctite them in

Is this a bodge? Or is it ok?

Time will tell, and the stresses of everyday use are a good test bed.

It's a little bit of a bodge, but hey, if it works, it works.

Here's a description of my bodge, and it seems to work just fine. I read rhm's post in the thread http://www.bikeforums.net/showthread...raleigh+twenty , and realized that he was exactly correct- after rethreading the BB shell, you would only have 3 good threads left. I really didn't want to alter my BB too much, and I'm way too cheap to buy Phil retaining rings let alone Phil's whole bottom bracket assembly. Anyway, I hear horror stories about the threading in the shell being too shallow for the Phil cups, etc.

So, first I ground away 3 mm of the BB shell to make it 73 mm wide, taking care to dress it flat and square with a file (no BB shell facing tool). Then I ground all but the last three rows of threading from the right-hand side of a 73 mm Shimano UN54 BB, making sure to not crush the transition threads, dressing them up with a needle file. Then I ground and filed most of the threading from the left-side (plastic) retaining cup, leaving more material since it's alot softer than the BB shell and a tight fit is good. Here are a couple of pics:

http://i271.photobucket.com/albums/j...B20section.jpg
A rethreaded BB shell and a 24 TPI cup installed. Note only about 3 good threads every half-inch.
(thanks to rhm)


http://i271.photobucket.com/albums/j...m_bracket2.jpg
My modified BB, retaining 3 good rows of 24 TPI threading on the body, filing away most of the threading on the plastic retaining cup.


http://i271.photobucket.com/albums/j...m_bracket3.jpg
The BB installed. The body screws in easily, and the cup is a bit snug, as it should be. No creaking or clicking (yet). Total cost: 20 bucks and about a half-hour work. Another good thing is that the original cups and axle still work fine, too.

Yeah think I'll go and build it up.

Wonder if those 24X 1 3/8" wheels that I found in my silver shed will fit it too.

Squeazel: Mate you're a bloody genius! Definitely 1st prize! :beer:

Nice...

R-20's : A thinkin' man's bike...

come check the progress...
http://web.mac.com/phatatude/Green_S...enty_Blog.html

Thanks, Jur, but I owe the idea to rhm (Rudi). Amazing what you can do with a bench grinder- after the sledgehammer, it's my favorite tool ;)

And, alecw, I was thinking about whether the cups would loosen up on you, and I believe the cups will tend to *tighten* from precession. So if the BB you have in there doesn't shift around now, I bet it will stay snug over time.

I know this is old thread, but....


I am thinking of attempting the same mod to my Twenty that you appear to have successfully managed Squeazel and I wanted to ask what size UN54 (shell width and axle width) you used? I am aiming to have a single front chainring on my Twenty so a good chainline is going to be important.


Any advice you can give me would be greatly received!


Many thanks!


Daz

You could search the forums but also the internet if no reply here. Plenty of info about upgrading these bikes floating around.

You could start with the legendary Sheldons pages: http://sheldonbrown.com/raleigh-twenty.html

My P20 had it's bottom bracket re-threaded 4 years ago (by me) and has seen some extreme use and mileage and everything is snug as a bug... the P20 had a 72.5mm shell so I did not have to re-face it.

Since then I have repeated this procedure on quite a number of R20 bottom brackets, re-threading them and facing them down to 73mm as when you try to fit a 68mm cartridge and are looking to face the bottom bracket, you start getting into the chain stay welds which is absolute hell on tools.

I suggest that blue loctite is used when the cartridge is installed as this will ensure that the cartridge remains secure and it also acts as an anti seize.

Thanks guys....I can find plenty of info about the shell width and which cartridge to use (the 73mm one!) but it's the actual axle/spindle width I'm struggling with....

The advice seems to vary from 110mm all the way up to over 130mm....

Width of the BB will always depend on the cranks you using in addition to the frame width. Roger

Thanks Roger....I guess I need to get my cranks first then!?

I think I used a 120 mm width. But it's more a matter of getting the chainline right, so the BB width required will depend on the cranks selected and the desired chainline. Me, I had to cold-set the rear triangle to 135 mm to fit a drum-brake SA 8-speed IGH, so the chainline was pretty wide. Measure the distance to the sprocket from the dropout, subtract that distance from half of the dropout O.L.D.- that's the chainline. Then somehow measure how far the chainring is from the end of the axle when looking from above when the crank is installed, add that distance to the chainline measurement, then double it- that will be your BB width. Make sure to use the same taper on the axle you measure with and the BB you eventually buy- Shimano is JIS taper, of course.

-Cycle_Maven
(used to be known in these parts as Squeazel)

Thanks very much!

I am using a flip-flop track hub on the rear so I will get the tape measure out!

20's are still the ride of choice...

R 20's - "Get better with age..."

My P20 has a slight offset at the BB with the 73 mm shell and I am using a 110mm spindle with a modified triple that has a 40/50/53 crank. I designed my rear triangle with a slight offset to give the bike a better chainline with the triple where I spend a lot of time in the 50 and 53 tooth chain ring and much less time in the 40 tooth granny.

The offset on the Raleigh bb was done to give a better chainline with an AW hub so if you reface the bottom bracket you have to keep this in mind.

Remember that the Raleigh Twenty has a bottom bracket that should be 76 but may vary by .5 - 1 mm and installing a 73mm cartridge requires refacing of the bottom bracket shell to 73mm.