Weird square taper diameter issue!
09-18-18, 11:26 AM
#1
Senior Member
Thread Starter
Join Date: Oct 2008
Location: Frankfurt, Germany
Posts: 1,544
Bikes: Focus trash find commuter, Eddy Merckx Corsa, BP Stealth TT bike, Leader 720 TT bike, Boardman Comp Hybrid drop bar conversion, Quantec CX budget cyclocross build, SerottaNOS frameset ready to build up!
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 128 Post(s)
Liked 104 Times
in
69 Posts
Weird square taper diameter issue!
Hi all,
Today’s job was swapping in a new 50/34 crankset.
I couldn’t get the FD to shift into the big ring, no problem, I’m sure there’s a new BB in the parts bin.... go to fit it but the diameter of the BB too big for the frame!
What’s that all about? I know about the different threadings but a whole new diameter?
Any ideas?
Today’s job was swapping in a new 50/34 crankset.
I couldn’t get the FD to shift into the big ring, no problem, I’m sure there’s a new BB in the parts bin.... go to fit it but the diameter of the BB too big for the frame!
What’s that all about? I know about the different threadings but a whole new diameter?
Any ideas?
09-18-18, 11:46 AM
#2
Senior Member
Thread Starter
Join Date: Oct 2008
Location: Frankfurt, Germany
Posts: 1,544
Bikes: Focus trash find commuter, Eddy Merckx Corsa, BP Stealth TT bike, Leader 720 TT bike, Boardman Comp Hybrid drop bar conversion, Quantec CX budget cyclocross build, SerottaNOS frameset ready to build up!
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 128 Post(s)
Liked 104 Times
in
69 Posts
The BB I wanted to use was a Shimano UN-91, spindle length 108mm
it had a cup diameter of 35.7mm
The one that came out had a cup diameter of 34,6mm.
Thoughts?
it had a cup diameter of 35.7mm
The one that came out had a cup diameter of 34,6mm.
Thoughts?
09-18-18, 12:10 PM
#3
Senior Member
Join Date: Jan 2009
Location: San Diego, CA
Posts: 3,672
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 836 Post(s)
Liked 1,061 Times
in
745 Posts
Is your new bb an Italian threaded version which has a 36mm O.D.? Should also mention that the UN-91 is a top end XTR Mountain Bike BB and no longer in production. Could be worth a fair amount as NOS especially if it's Italian thread.
Last edited by Crankycrank; 09-18-18 at 12:30 PM.
09-18-18, 12:23 PM
#4
Senior Member
Thread Starter
Join Date: Oct 2008
Location: Frankfurt, Germany
Posts: 1,544
Bikes: Focus trash find commuter, Eddy Merckx Corsa, BP Stealth TT bike, Leader 720 TT bike, Boardman Comp Hybrid drop bar conversion, Quantec CX budget cyclocross build, SerottaNOS frameset ready to build up!
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 128 Post(s)
Liked 104 Times
in
69 Posts
Nope, standard BSA! Maybe the un91 BB has Italian threading?
09-18-18, 12:27 PM
#5
Senior Member
Thread Starter
Join Date: Oct 2008
Location: Frankfurt, Germany
Posts: 1,544
Bikes: Focus trash find commuter, Eddy Merckx Corsa, BP Stealth TT bike, Leader 720 TT bike, Boardman Comp Hybrid drop bar conversion, Quantec CX budget cyclocross build, SerottaNOS frameset ready to build up!
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 128 Post(s)
Liked 104 Times
in
69 Posts
36 x 24T 70 on the drive side cup, that’s Italian, right?
09-18-18, 01:13 PM
#7
Senior Member
Thread Starter
Join Date: Oct 2008
Location: Frankfurt, Germany
Posts: 1,544
Bikes: Focus trash find commuter, Eddy Merckx Corsa, BP Stealth TT bike, Leader 720 TT bike, Boardman Comp Hybrid drop bar conversion, Quantec CX budget cyclocross build, SerottaNOS frameset ready to build up!
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 128 Post(s)
Liked 104 Times
in
69 Posts
Oops sorry, I misread! Well, looks like the mystery is solved and the correct BB ordered!
cheers all
Simon
cheers all
Simon
09-18-18, 01:13 PM
#8
Senior Member
Thread Starter
Join Date: Oct 2008
Location: Frankfurt, Germany
Posts: 1,544
Bikes: Focus trash find commuter, Eddy Merckx Corsa, BP Stealth TT bike, Leader 720 TT bike, Boardman Comp Hybrid drop bar conversion, Quantec CX budget cyclocross build, SerottaNOS frameset ready to build up!
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 128 Post(s)
Liked 104 Times
in
69 Posts
I’ll stick the UN91 on the Bay as I have no use for it.
09-18-18, 01:26 PM
#9
Banned
Facet profiles are where the differences are in square taper ; taper 2 degrees,
but JIS and ISO differ in widths across the facets..
JIS Cranks wont go very far on an ISO Spindle , inverse mismatch.. and arm goes on too far on a JIS BB
But some European Companies make Cranks using JIS taper interfaces....
nothing is simple..
..
but JIS and ISO differ in widths across the facets..
JIS Cranks wont go very far on an ISO Spindle , inverse mismatch.. and arm goes on too far on a JIS BB
But some European Companies make Cranks using JIS taper interfaces....
nothing is simple..
..
09-19-18, 01:20 AM
#10
Senior Member
Thread Starter
Join Date: Oct 2008
Location: Frankfurt, Germany
Posts: 1,544
Bikes: Focus trash find commuter, Eddy Merckx Corsa, BP Stealth TT bike, Leader 720 TT bike, Boardman Comp Hybrid drop bar conversion, Quantec CX budget cyclocross build, SerottaNOS frameset ready to build up!
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 128 Post(s)
Liked 104 Times
in
69 Posts
Thanks Bob, all interesting stuff.
Let’s hope the BB I have ordered works. The crankset will sit 5mm more inboard so that should be plenty.
Frustratingly, I could have used that Italian-threaded square taper BB a couple of years ago, when I was building up my Merckx Corsa Extra, but I didn’t know what I had in the parts bin! Grr!
Let’s hope the BB I have ordered works. The crankset will sit 5mm more inboard so that should be plenty.
Frustratingly, I could have used that Italian-threaded square taper BB a couple of years ago, when I was building up my Merckx Corsa Extra, but I didn’t know what I had in the parts bin! Grr!
