Just went to install a Shimano BB-UN73 bottom bracket (square taper) on my Surly Long Haul Trucker, and I'm having problems installing the left side cup.
The bottom bracket is the correct width - 68mm - for the frame. The LBS faced and chased the shell. The right side threaded in just fine and torqued down properly.
The left side cup is plastic. I've greased the cup threads and applied a little grease to the inside of the cup but it doesn't seem to be threading in correctly. That is, I'm probably about 1/4" - 3/8" from having the cup snuggle up agains the frame and I'm encountering *considerable* resistance to further tightening. I hand-threaded the cup into the frame up to that point, so I know it's not cross-threaded. The torque at this point is starting to approach final torque and I don't want to continue and possibly bugger things up.
What's going on here? Is this normal behaviour for a plastic cup?
you are finished tightening that left cup. Stop tightenting it. that is the way it works. It does not necessarily bottom flush to the tubing, I just did my brothers bike and same thing it did not go in all the way. "TomYoung" <[email hidden]> wrote in message news:[email hidden]...
Quoted message said:
Hi all:
Just went to install a Shimano BB-UN73 bottom bracket (square taper) on my Surly Long Haul Trucker, and I'm having problems installing the left side cup.
The bottom bracket is the correct width - 68mm - for the frame. The LBS faced and chased the shell. The right side threaded in just fine and torqued down properly.
The left side cup is plastic. I've greased the cup threads and applied a little grease to the inside of the cup but it doesn't seem to be threading in correctly. That is, I'm probably about 1/4" - 3/8" from having the cup snuggle up agains the frame and I'm encountering *considerable* resistance to further tightening. I hand-threaded the cup into the frame up to that point, so I know it's not cross-threaded. The torque at this point is starting to approach final torque and I don't want to continue and possibly bugger things up.
What's going on here? Is this normal behaviour for a plastic cup?
you are finished tightening that left cup. Stop tightenting it. that is the way it works. It does not necessarily bottom flush to the tubing, I just did my brothers bike and same thing it did not go in all the way. "TomYoung" <[email hidden]> wrote in message news:[email hidden]...
Quoted message said:
Hi all:
Just went to install a Shimano BB-UN73 bottom bracket (square taper) on my Surly Long Haul Trucker, and I'm having problems installing the left side cup.
The bottom bracket is the correct width - 68mm - for the frame. The LBS faced and chased the shell. The right side threaded in just fine and torqued down properly.
The left side cup is plastic. I've greased the cup threads and applied a little grease to the inside of the cup but it doesn't seem to be threading in correctly. That is, I'm probably about 1/4" - 3/8" from having the cup snuggle up agains the frame and I'm encountering *considerable* resistance to further tightening. I hand-threaded the cup into the frame up to that point, so I know it's not cross-threaded. The torque at this point is starting to approach final torque and I don't want to continue and possibly bugger things up.
What's going on here? Is this normal behaviour for a plastic cup?
TIA.
Tom Young
After taking thing apart a couple of times and looking at all the pieces more closely it finally dawned on me what the problem was: the left-side cup was for a 73mm bottom bracket! After taking it back to the shop and pawing through their bottom bracket boxes it was also pretty apparent that the cup was also designed for a different Shimano bottom bracket than the one I had. That one was never going to work.
I finally found a left side cup in their stash (used) that seems to fill the bill and snugs up nicely to the shell, with maybe an 1/8" or 1/16" sticking out. I think that's the right cup but since Shimano doesn't have a parts diagram available I'm not entirely sure.
Just went to install a Shimano BB-UN73 bottom bracket (square taper) on my Surly Long Haul Trucker, and I'm having problems installing the left side cup.
The bottom bracket is the correct width - 68mm - for the frame. The LBS faced and chased the shell. The right side threaded in just fine and torqued down properly.
The left side cup is plastic. I've greased the cup threads and applied a little grease to the inside of the cup but it doesn't seem to be threading in correctly. That is, I'm probably about 1/4" - 3/8" from having the cup snuggle up agains the frame and I'm encountering *considerable* resistance to further tightening. I hand-threaded the cup into the frame up to that point, so I know it's not cross-threaded. The torque at this point is starting to approach final torque and I don't want to continue and possibly bugger things up.
What's going on here? Is this normal behaviour for a plastic cup?
TIA.
Threads need to be chased farther into the BB shell.
"Qui si parla Campagnolo" <[email hidden]> wrote in message news:[email hidden]...
Quoted message said:
TomYoung said:
Hi all:
Just went to install a Shimano BB-UN73 bottom bracket (square taper)
on
Quoted message said:
Quoted message said:
my Surly Long Haul Trucker, and I'm having problems installing the
left
Quoted message said:
Quoted message said:
side cup.
The bottom bracket is the correct width - 68mm - for the frame. The LBS faced and chased the shell. The right side threaded in just
fine
Quoted message said:
Quoted message said:
and torqued down properly.
The left side cup is plastic. I've greased the cup threads and
applied
Quoted message said:
Quoted message said:
a little grease to the inside of the cup but it doesn't seem to be threading in correctly. That is, I'm probably about 1/4" - 3/8"
from
Quoted message said:
Quoted message said:
having the cup snuggle up agains the frame and I'm encountering *considerable* resistance to further tightening. I hand-threaded
the
Quoted message said:
Quoted message said:
cup into the frame up to that point, so I know it's not
cross-threaded.
Quoted message said:
Quoted message said:
The torque at this point is starting to approach final torque and I don't want to continue and possibly bugger things up.
What's going on here? Is this normal behaviour for a plastic cup?
TIA.
Threads need to be chased farther into the BB shell.
Correct answer. (Have someone with a Campy BB threading tool chase it out to Italian 36mm x 24 TPI 55° threads because they are superior). ;-)
Kidding aside, many frames have very poorly tapped threads in the bottom brackets. There could be a glop of brazing material deep inside the BB that didn't get threaded properly. Also, lots of crud.
Most steel BB cups only have 1/2" - 5/8" of thread versus the Shimano plastic "cups" that have at least 3/4" of thread so the steel cups work without any problem.
I had a similar problem with a Shimano BB that I bought a few month months ago at a LBS. I got home and went to install it and one of the cups was for a different make BB.
