68 vs 73 bottom bracket?

(Mark) said:

Simple question, but I can't seem to find the answer anywhere.

I took home a 73x107 sealed cartridge BB (Shimano UN52). But when I
put it up against another 68 I have at home, it's the identical length
(these are for two different bikes). I expected the body of the BB to
be 5mm longer -- 73mm vs 68mm.

A reasonable assumption, overall. (I am, myself, assuming that the
word "another" was inserted in error.)

Quoted message said:

On top of that, when I slip on the adjustable cups onto both BBs, they
still match up exactly in length. So where's the extra 5mm?

Not present?

Quoted message said:

The BB was an open-box NOS, so it's possible that they gave me the
wrong adjustable cup. Is it possible that the only difference between
a 68 vs a 73 BB might be in the adjustable cup?

That should not be the case; the shaft must extend outward from each
side equally, and if only the right side were different between the 68
and 73, the shaft would be off-center in at least one of the
instances.

Quoted message said:

The UN52 is marked as a 73mm, so unless it was mis-labeled, it doesn't
make sense that both BB bodies are the same length. The right side
has built-in threads and a flange; the left side adjustable cup also
has a flange, so it couldn't screw deep into the bottom bracket. If
the adjustable cup doesn't tighten up to the BB body, the left side of
the BB will float free, which can't be good.

I've had other interesting adventures with a Shimano UN52 myself. In
one particularly memorable instance, the unthreaded shoulder between
the threads and the flange on the right-hand end was large enough that
the BB flange did not bottom on the BB shell of the frame before the
recommended installation torque was achieved. After some futzing
around, I swapped to a generic BB (at a lower price) which had threads
all the way to the flange, and had no problems. The UN52 finally got
used on a different bike...and the taper must have been screwy,
because the cranks (which had run at the correct offset with the
original Shimano BB) suddenly were at least 4mm too close to the seat
tube; so close that it was impossible to trim the fder to get a shift
on to the granny gear. (I say 4mm because a 3mm shim between the BB
and the frame didn't fix it, but adding another 1.5mm shim did, just
barely.)

Quoted message said:

What's going on here???

Beat me, but I got around such worries by not using the Shimano UN52.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
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"Mark" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Simple question, but I can't seem to find the answer anywhere.

I took home a 73x107 sealed cartridge BB (Shimano UN52). But when I
put it up against another 68 I have at home, it's the identical length
(these are for two different bikes). I expected the body of the BB to
be 5mm longer -- 73mm vs 68mm.

On top of that, when I slip on the adjustable cups onto both BBs, they
still match up exactly in length. So where's the extra 5mm?

The BB was an open-box NOS, so it's possible that they gave me the
wrong adjustable cup. Is it possible that the only difference between
a 68 vs a 73 BB might be in the adjustable cup?

The UN52 is marked as a 73mm, so unless it was mis-labeled, it doesn't
make sense that both BB bodies are the same length. The right side
has built-in threads and a flange; the left side adjustable cup also
has a flange, so it couldn't screw deep into the bottom bracket. If
the adjustable cup doesn't tighten up to the BB body, the left side of
the BB will float free, which can't be good.

What's going on here???

-- Mark

The difference is in the width of the BB shell, not the lenght of the BB or
the axle.

Graham

i looked at a pair of old campy bb's yesterday, one frendh 68 and on
italian 72?. the 72 was was slightly longer inside, ie the bearing
seats were spaced further apart and the whole spindle was slightly
longer too.

bill

Mark said:

Simple question, but I can't seem to find the answer anywhere.

I took home a 73x107 sealed cartridge BB (Shimano UN52). But when I
put it up against another 68 I have at home, it's the identical length
(these are for two different bikes). I expected the body of the BB to
be 5mm longer -- 73mm vs 68mm.

On top of that, when I slip on the adjustable cups onto both BBs, they
still match up exactly in length. So where's the extra 5mm?

The BB was an open-box NOS, so it's possible that they gave me the
wrong adjustable cup. Is it possible that the only difference between
a 68 vs a 73 BB might be in the adjustable cup?

The UN52 is marked as a 73mm, so unless it was mis-labeled, it doesn't
make sense that both BB bodies are the same length. The right side
has built-in threads and a flange; the left side adjustable cup also
has a flange, so it couldn't screw deep into the bottom bracket. If
the adjustable cup doesn't tighten up to the BB body, the left side of
the BB will float free, which can't be good.

What's going on here???

-- Mark

Werehatrack said:

On 9 Sep 2004 13:36:11 -0700, [email hidden] (Mark) wrote:

... the shaft must extend outward from each
side equally, and if only the right side were different between the 68
and 73, the shaft would be off-center in at least one of the
instances.

Must is a pretty strong word... I have an old Bianchi with an oddball combo of parts. It runs fine on an assymmetric BB. (which compensates for the crank arms being of different makes...)

dabac said:

Werehatrack said:

On 9 Sep 2004 13:36:11 -0700, [email hidden] (Mark) wrote:

... the shaft *must* extend outward from each
side *equally*, and if only the right side were different between the
68
and 73, the shaft would be off-center in at least one of the
instances.

Must is a pretty strong word... I have an old Bianchi with an oddball
combo of parts. It runs fine on an assymmetric BB. (which compensates
for the crank arms being of different makes...)

To be compliant with any reasonable expectation, though,
nonproprietary replacement parts have to be predictable, and not
randomly strange. I could excuse a BB maker for letting the left end
of the shaft be a bit long or short for a specific OEM application
that needed it, but I could also excuse a distributor for rejecting
the entire shipment as being out of spec if they shipped those as
generic replacements with a misleading set of specs.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Original poster here, with what I've discovered....

The puzzle would probably be easy to solve if I had a basket full of
parts, or a LBS handy to let me browse through their shop.

But I think I've found that the 'only' difference between a UN52
"68mm" BB an a UN52 "73mm" BB is the adustable cup. The cup for a 73
looks to be about 5mm deeper -- I can count 5 or 6 additional threads
in comparison photos.

See here for a 68:
http://store.airbomb.com/ba/asp/ic.CR4963/ab/Itemdesc.htm

See here for a 73:
http://store.airbomb.com/ba/asp/ic.CR4969/ab/Itemdesc.htm

Each of those two pages has a tiny picture of the part; click on that
picture to show a large photo. The 73mm BB has a noticeably larger
adjustable cup.

So I'm almost convinced that both the UN52 68 and the 73 use the same
BB body, just different plastic adjustable cups. I don't like
this.... The BB I'm replacing is a Specialized brand and its body is
longer than the UN52, meaning that the bearings are farther outboard
on the Specialized. That design should be stronger. (Unfortunately
it seized up...)

So the shop gave me the wrong adjustable cup. I returned the whole
thing anyway.

Thanks for the comments -- sorry if I wasn't too clear at first.

-- Mark

(Mark) said:

Original poster here, with what I've discovered....

The puzzle would probably be easy to solve if I had a basket full of
parts, or a LBS handy to let me browse through their shop.

But I think I've found that the 'only' difference between a UN52
"68mm" BB an a UN52 "73mm" BB is the adustable cup. The cup for a 73
looks to be about 5mm deeper -- I can count 5 or 6 additional threads
in comparison photos.

See here for a 68:
http://store.airbomb.com/ba/asp/ic.CR4963/ab/Itemdesc.htm

See here for a 73:
http://store.airbomb.com/ba/asp/ic.CR4969/ab/Itemdesc.htm

Each of those two pages has a tiny picture of the part; click on that
picture to show a large photo. The 73mm BB has a noticeably larger
adjustable cup.

For a complete comparison, the two units would have to be measured for
shaft protrusion on the right; it's very likely that (for instance) a
68/117 and 73/117 BB might have the same body but either a different
shaft or a different final pressed position of the shaft, with a
different matching right plastic part depending on the overall width.
The two complete assemblies should still be different in more than
just the dimensions of that plastic cup.

--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

(Mark) said:

The UN52 is marked as a 73mm, so unless it was mis-labeled, it doesn't
make sense that both BB bodies are the same length. The right side
has built-in threads and a flange; the left side adjustable cup also
has a flange, so it couldn't screw deep into the bottom bracket. If
the adjustable cup doesn't tighten up to the BB body, the left side of
the BB will float free, which can't be good.

For that series of bb, the body is the same for 68 and 73. Only the
cups are different.

I am experiencing a similar problem with a FSA Platinum Pro CroMo ISIS
bottom bracket. It's a 68mm bottom bracket, but the left side cup
appears to be wide enough for a 73mm bb shell. So when installed there
are threads exposed. Tacky. And annoying. Anybody else experience
this?

Cheers,

UberFranz

Uber Franz said:

I am experiencing a similar problem with a FSA Platinum Pro CroMo ISIS
bottom bracket. It's a 68mm bottom bracket, but the left side cup
appears to be wide enough for a 73mm bb shell. So when installed there
are threads exposed. Tacky. And annoying.

And probably creaky.

In article <[email hidden]>,

Uber Franz said:

I am experiencing a similar problem with a FSA Platinum Pro CroMo ISIS
bottom bracket. It's a 68mm bottom bracket, but the left side cup
appears to be wide enough for a 73mm bb shell. So when installed there
are threads exposed. Tacky. And annoying. Anybody else experience
this?

Yes, but not to the same extent as you: no threads are exposed in my
case. When the inner flange of my Truvativ ISIS BB's
(BB-02-SPL-DH-118-68/68E/73) left cup bottoms out, there is a gap of 2
or 3mm at the (68mm) BB shell. I assume this is normal given this BB's
model designation ("68/68E/73"😉; after 1000 km or so, the setup has not
caused any problems.

UF, perhaps your BB is designed to accommodate both 68 and 73mm shell
widths.

luke

Luke, I think you might be right. I called Excel and talked to one of
their tech guys who said this is just the way FSA makes their BBs. Oh
well, I just hope it doesn't start creaking. I'll keep you posted.

On 4 Jan 2005 09:59:51 -0800 "Uber Franz" <[email hidden]>

Quoted message said:

I am experiencing a similar problem with a FSA Platinum Pro CroMo ISIS
bottom bracket. It's a 68mm bottom bracket, but the left side cup
appears to be wide enough for a 73mm bb shell. So when installed there
are threads exposed. Tacky. And annoying. Anybody else experience
this?

It's not that the cup is too wide; it's that the distance between the
races on the spindle is too large. Do they make a more appropriate
spindle?

-
-----------------------------------------------
Jim Adney [email hidden]
Madison, WI 53711 USA
-----------------------------------------------

On Wed, 05 Jan 2005 17:32:47 -0600, Jim Adney <[email hidden]>

Quoted message said:

On 4 Jan 2005 09:59:51 -0800 "Uber Franz" <[email hidden]>

Quoted message said:

I am experiencing a similar problem with a FSA Platinum Pro CroMo ISIS
bottom bracket. It's a 68mm bottom bracket, but the left side cup
appears to be wide enough for a 73mm bb shell. So when installed there
are threads exposed. Tacky. And annoying. Anybody else experience
this?

It's not that the cup is too wide; it's that the distance between the
races on the spindle is too large. Do they make a more appropriate
spindle?

-
-----------------------------------------------
Jim Adney [email hidden]
Madison, WI 53711 USA
-----------------------------------------------

Not an FSA, but TruVativ has the same characteristic and specifically
mentions it in their manual. Mine even has an O-ring to hide the gap.

From http://www.truvativ.com/manuals/2005/BB-GigaPipe-e-r2.pdf, bottom
of the third column:

"The cup flange will NOT bottom against the left face of the frame
shell."

In article <[email hidden]>, dianne_1234

Quoted message said:

Not an FSA, but TruVativ has the same characteristic and specifically
mentions it in their manual. Mine even has an O-ring to hide the gap.\

With my Truvativ BB, neither was an O-ring supplied nor a gap mentioned
in the manual. Mind you, the Truvativ model I installed is a few years
old­it even includes a spacer for accommodating non E-type derailleurs
(now defunct?). It seems Truvativ updated their literature and
accessories in later BB models.

Quoted message said:

From http://www.truvativ.com/manuals/2005/BB-GigaPipe-e-r2.pdf, bottom
of the third column:

"The cup flange will NOT bottom against the left face of the frame
shell."

Thanks for the info.

luke