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The UN72 problem

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The UN72 problem

Old 05-27-09, 04:10 PM
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stevegor
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The UN72 problem

As R20 owners know, one of the ways of using modern cranks is to use a Shimano 73mm UN72 BB with Phil rings, however these BBs are becoming increasingly more difficult to find, especially in the correct spindle length. Phil BBs are also very expensive, so most don't go that way, I therefore propose another solution.

Why not simply buy any Shimano 73mm BB, remove the threaded cap, then lathe off the thread that is on the other end of the BB's body, surely if done correctly it could work.
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Old 05-27-09, 04:49 PM
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I contemplated exactly this idea when thinking about mine. I'm convinced it would work.
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Old 05-27-09, 04:57 PM
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Originally Posted by jur View Post
I contemplated exactly this idea when thinking about mine. I'm convinced it would work.

Well Jur, my son is doing Engineering at school, he's working with lathes designing and making components for his recumbent so this wouldn't be too hard for him to do. I will buy a 73mm BB and see what happens....stay tuned.

BTW, unlike his brain-dead father, the lad is very talented.
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Old 05-27-09, 06:29 PM
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surely it's possible to try on cheaper UN-5x BBs as well.

I'm in the same boat, need one of those, or a long cotterless axle that will fit the R20 BB.
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Old 05-27-09, 07:23 PM
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AEO,

I tried the No.7 size cotterless axle from Harris Cyclery but the bearing races where the Raleigh cups meet were not the same width apart as the original Raleigh axle. I just couldn't get enough adjustment to tighten the axle, so I opted out for the UN72 route.

When I make my weekly pilgrimage to my LBS I will check out what 73mm BBs are available and buy one.
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Old 05-27-09, 08:48 PM
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I used a Tange BB with steel cups and forced the 24 TPI threads in the 26 TPI Raleigh BB shell and it worked. Truvativ have a BB with aluminum removable shells, probably they can be forced as well and it might work. Other idea I had, was using a Shimano BB, lathe the fixed cup thread (just like you fellows said) insert it in the R20 BB, reinforce with epoxy glue and force the plastic cup from the other edge.
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Old 05-28-09, 04:30 AM
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i had my b shell rethreaded to use the 72 but unfortunately the threads weren't deep enough. looking through the junk drawer at the lbs i found a un25 which has shorter cups. the fixed cup went in all the way. on the other side the plastic cup was a few mm loose since i didn't cut the bb shell. what i did was i ground off the lip at the top to get a few more turns into the shell. it got close but no cigar. fortunately i found a spacer in the junk drawer that filled the gap and got my bb nice and tight. i've got about 50 miles on my r20 so far and not one problem has arisen. the chain is straight and bb is tight. btw i used a 113 spindle and by some stroke of luck, had a perfect chainline first try.
after reading all the web info i thought the un72 was the way to go too but after many hours of fiddling it was time to rethink. just passing on what worked for me.
one more thing. i've seen alot of info that says the qr lever on an r20 is threaded 3/8-20. that's incorrect. its actually 3/8-16tpi. that too can cause a ton of frustration if you need to make the bolt as i did.
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Old 05-28-09, 10:42 AM
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Sturmey Archer cog spacers fit on BB cups to space them.
I put them on my Vindec racer ages ago
My Dawes Galaxy had them when I got it.
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Old 05-28-09, 10:49 AM
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I have refitted two Phillip's 20's and was lucky that their bb width is 72-73 mm (not very precise machining on Raleigh's part) so re-tapping the bb to 24 tpi and using a 73 mm bb has worked very well.

Having experience in running a lathe I cannot see what it would be difficult to remove the drive side threads from a 73 mm bb... it would take longer to chuck it up and dial it in than it would to remove the threads although the insert would probably have to be carbide as that is some very hard steel.

With that being said... if I had access to a lathe I'd probably make my own retaining rings as any threading would be possible.
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Old 05-28-09, 10:57 AM
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The guys in C&V have done this mod from what I remember. Anyone cowering near State College PA that wants to try this can PM me and we can use my lathe.
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Old 05-29-09, 08:18 AM
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Hi Guys
I work in a LBS and one of our suppliers sells a bb that doesnt require threads,
It`s designed to use on frames with damaged threads,
It`s only available in 68mm but various axle lengths,
If you grind down the width of the bb shell and have it faced by your lbs you should be sorted
for half the price of the Phil Woods cups
Cheers
Adrian
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Old 05-29-09, 09:28 AM
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One could also drop the coin for a Phil Wood bb to go with the cups and never have to service your 20 again...

That's a $170.00 touch though.
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Old 05-29-09, 01:57 PM
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Ive narrowed and rettaped a few old Raleighs.

I got a Giant Boulder that had a smooth cup BB cartridge. Was old and worn out.
A different brand that can be bought in different shell width and axle widths.
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Old 05-29-09, 02:12 PM
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This is one of the intriguing, frustrating, challenging and enjoyable aspects that makes restoring/modding our beloved 20s so interesting.......you've gotta be a nutter.
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Old 05-29-09, 10:00 PM
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Originally Posted by 75PIN View Post
Hi Guys
I work in a LBS and one of our suppliers sells a bb that doesnt require threads,
It`s designed to use on frames with damaged threads,
It`s only available in 68mm but various axle lengths,
If you grind down the width of the bb shell and have it faced by your lbs you should be sorted
for half the price of the Phil Woods cups
Cheers
Adrian
Two aspects on this type of BB. First if you can get an old Mavic cartridge BB from the 80's it used a similar principle with a threaded BB and two threaded rings to lock it against the BB shell.

Second, Sheldon Brown referred that these type of YST BB cartridges do not fit inside an ordinary British/ISO BB shell, requiring machining, destroying the original threads, and, in the case of the R20, it is almost impossible to use this YST because the BB shell is already too thin.
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Old 05-29-09, 10:07 PM
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Originally Posted by stevegor View Post
This is one of the intriguing, frustrating, challenging and enjoyable aspects that makes restoring/modding our beloved 20s so interesting.......you've gotta be a nutter.
I should be committed actually...

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Old 05-30-09, 03:20 AM
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.....I'm posting this from the local asylum.
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Old 05-30-09, 04:49 AM
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Has anybody actually ground down and refaced? My LBS has the Park facing/threading tool available I am still running the OEM crank for the time being and probably will for a bit longer until I get a few other things dialed in.

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Old 05-30-09, 05:23 PM
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Jur has had his R20's BB shell cut down to 68mm then threaded to 24tpi, we've communicated about a few times because I'm thinking of doing the same.

As for the YST BB, do they come in 73mm?
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Old 05-31-09, 09:25 AM
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Hi
As far as i know 68mm only,
But i`ll check when i go back to work on tuesday

Cheers
Adrian
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Old 05-31-09, 04:25 PM
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I searched for Threadless Bottom Bracket Cartridge

Heres an Acor one.
https://www.freemanscycles.co.uk/prod...Bracket%20unit

A pristine BB Cartridge that has a 70mm BB shell width.
https://www.sjscycles.co.uk/product-P...eads-16505.htm

Seen on a Fixed gear website that a man had fallen off his bike due to the BB loosening. But think he had not installed it properly. Plus single speed strains the BB more than geared bikes
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Old 06-01-09, 10:22 PM
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Originally Posted by stevegor View Post
Jur has had his R20's BB shell cut down to 68mm then threaded to 24tpi, we've communicated about a few times because I'm thinking of doing the same.
That's exactly what I did. I ground 2.5mm off each side of the BB shell. then faced by eye with a hand file. The retapping the threads was key! A friend at the local bike shop had the right tool; a
Campagnolo threading tool which engages the left side and right side threads at the same time. The guiding bar fits all the way through the bb shell and centers the tool without any undesired influence from the grinding and handwork. I'm using a standard cartridge 68mm BB plus a bit of thread locking compound. no special orders. No problems.
Good luck, G.R.
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Old 06-02-09, 03:16 AM
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when I worked at Halfords there was a bb tapping tool. Think it was Var, had light blue grips.
I would rettap the BB till the tool bottomed out in the shell.
then screw a flat faced cup and cone type adjustable cup in.
I could then cut a bit off the side of the BB shell and file it flat against the BB cup. would be nice and flat. and taking the cup out would debur the edge of the shell.
bit more work cutting and facing the drive side cup though.
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