weird bb problem?

In building up a Surly Long Haul Trucker for a friend, I encountered
this problem: The BB we used is a Shimano UN-73, with stock plastic
shoulderless left adapter cup. The left cup cracked during installation
while at less than final torque. I've eaten through plenty of left cups
now on this frame and they keep dying - one did it at very low torque,
I think even before the cup bottomed out on the BB. I currently have it
set up using a steel adapter cup off some other Shimano BB that seems
to work fine. While installing the steel one, it went in somewhat
rough, and I removed it and looked at the inside and there are gouges
where it was presumably rubbing against the BB. The bearing feels
signficantly less than perfect when everything is all tightened down.

What I'm guessing is going on is that the BB shell threads are out of
line with each other enough to cause all this. I don't see how a facing
error could cause this - could it?

I don't have access to piloted BB taps and am not familiar with using
them. My concern with chasing this frame's threads with piloted taps is
that if the error in the shell thread alignment is really bad, how
would just forcing piloted taps through it all work without ruining the
integrity of the threads? It seems like there's a judgement call here
that needs to be made with that, but I have no idea how to make it.

We can still warranty the frame but I really don't want to.

"Nate Knutson" wrote:

In building up a Surly Long Haul Trucker for a friend, I encountered
this problem: The BB we used is a Shimano UN-73, with stock plastic
shoulderless left adapter cup. The left cup cracked during installation
while at less than final torque. I've eaten through plenty of left cups
now on this frame and they keep dying - one did it at very low torque,
I think even before the cup bottomed out on the BB. I currently have it
set up using a steel adapter cup off some other Shimano BB that seems
to work fine. While installing the steel one, it went in somewhat
rough, and I removed it and looked at the inside and there are gouges
where it was presumably rubbing against the BB. The bearing feels
signficantly less than perfect when everything is all tightened down.

What I'm guessing is going on is that the BB shell threads are out of
line with each other enough to cause all this. I don't see how a facing
error could cause this - could it?

I don't have access to piloted BB taps and am not familiar with using
them. My concern with chasing this frame's threads with piloted taps is
that if the error in the shell thread alignment is really bad, how
would just forcing piloted taps through it all work without ruining the
integrity of the threads? It seems like there's a judgement call here
that needs to be made with that, but I have no idea how to make it.

We can still warranty the frame but I really don't want to.

It sure sounds like threads that aren't lined up properly.

A piloted tap is really easy to use (but outrageously expensive to
buy). You simply set both taps in place (the "axle" through the
middle will keep them parallel) and start both of them lightly, then
start cutting threads, one side at a time. Unless the threads are WAY
out, I'm guessing that a piloted tap would clean up the threads just
fine.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Mark Hickey wrote:
"Nate Knutson" wrote:

In building up a Surly Long Haul Trucker for a friend, I encountered
this problem: The BB we used is a Shimano UN-73, with stock plastic
shoulderless left adapter cup. The left cup cracked during installation
while at less than final torque. I've eaten through plenty of left cups
now on this frame and they keep dying - one did it at very low torque,
I think even before the cup bottomed out on the BB. I currently have it
set up using a steel adapter cup off some other Shimano BB that seems
to work fine. While installing the steel one, it went in somewhat
rough, and I removed it and looked at the inside and there are gouges
where it was presumably rubbing against the BB. The bearing feels
signficantly less than perfect when everything is all tightened down.

What I'm guessing is going on is that the BB shell threads are out of
line with each other enough to cause all this. I don't see how a facing
error could cause this - could it?

I don't have access to piloted BB taps and am not familiar with using
them. My concern with chasing this frame's threads with piloted taps is
that if the error in the shell thread alignment is really bad, how
would just forcing piloted taps through it all work without ruining the
integrity of the threads? It seems like there's a judgement call here
that needs to be made with that, but I have no idea how to make it.

We can still warranty the frame but I really don't want to.

It sure sounds like threads that aren't lined up properly.

A piloted tap is really easy to use (but outrageously expensive to
buy). You simply set both taps in place (the "axle" through the
middle will keep them parallel) and start both of them lightly, then
start cutting threads, one side at a time. Unless the threads are WAY
out, I'm guessing that a piloted tap would clean up the threads just
fine.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

I agree that running a piloted tap through would probably solve the
problem unless it's bad enough, but on the other hand the issue is
pretty darn bad on this frame, and I have no idea where to draw this
particular line - and if I try the taps and it turns out that it cuts
away too much material and very bad things happen to the threads or
frame there, I'm worried that all I'm probably gonna be left with to
try and warranty is a frame that one could argue strongly looks to have
been mangled by incorrect use of BB taps.

Also I should mention FWIW that the individual BB parts thread in
perfectly smoothly when not interfacing with one another - could that
maybe indicate that the misalignment originated when the threads were
cut originally, rather than during welding?

On 31 Jul 2006 21:13:12 -0700, "Nate Knutson"
wrote:


Mark Hickey wrote:
"Nate Knutson" wrote:

In building up a Surly Long Haul Trucker for a friend, I encountered
this problem: The BB we used is a Shimano UN-73, with stock plastic
shoulderless left adapter cup. The left cup cracked during installation
while at less than final torque. I've eaten through plenty of left cups
now on this frame and they keep dying - one did it at very low torque,
I think even before the cup bottomed out on the BB. I currently have it
set up using a steel adapter cup off some other Shimano BB that seems
to work fine. While installing the steel one, it went in somewhat
rough, and I removed it and looked at the inside and there are gouges
where it was presumably rubbing against the BB. The bearing feels
signficantly less than perfect when everything is all tightened down.

What I'm guessing is going on is that the BB shell threads are out of
line with each other enough to cause all this. I don't see how a facing
error could cause this - could it?

I don't have access to piloted BB taps and am not familiar with using
them. My concern with chasing this frame's threads with piloted taps is
that if the error in the shell thread alignment is really bad, how
would just forcing piloted taps through it all work without ruining the
integrity of the threads? It seems like there's a judgement call here
that needs to be made with that, but I have no idea how to make it.

We can still warranty the frame but I really don't want to.

It sure sounds like threads that aren't lined up properly.

A piloted tap is really easy to use (but outrageously expensive to
buy). You simply set both taps in place (the "axle" through the
middle will keep them parallel) and start both of them lightly, then
start cutting threads, one side at a time. Unless the threads are WAY
out, I'm guessing that a piloted tap would clean up the threads just
fine.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

I agree that running a piloted tap through would probably solve the
problem unless it's bad enough, but on the other hand the issue is
pretty darn bad on this frame, and I have no idea where to draw this
particular line - and if I try the taps and it turns out that it cuts
away too much material and very bad things happen to the threads or
frame there, I'm worried that all I'm probably gonna be left with to
try and warranty is a frame that one could argue strongly looks to have
been mangled by incorrect use of BB taps.

Also I should mention FWIW that the individual BB parts thread in
perfectly smoothly when not interfacing with one another - could that
maybe indicate that the misalignment originated when the threads were
cut originally, rather than during welding?

Try a different BB, any BB, even the wrong length and see what
happens.

"Nate Knutson" wrote:

I agree that running a piloted tap through would probably solve the
problem unless it's bad enough, but on the other hand the issue is
pretty darn bad on this frame, and I have no idea where to draw this
particular line - and if I try the taps and it turns out that it cuts
away too much material and very bad things happen to the threads or
frame there, I'm worried that all I'm probably gonna be left with to
try and warranty is a frame that one could argue strongly looks to have
been mangled by incorrect use of BB taps.

If a (quality) piloted tap buggers up the threads so badly the frame
is ruined, the BB was buggered to start with. The threads have to be
cut in parallel, and if doing so causes them to go out of spec enough
to be unusable, it's a moot point... the frame wasn't useful as it
was, either.

Also I should mention FWIW that the individual BB parts thread in
perfectly smoothly when not interfacing with one another - could that
maybe indicate that the misalignment originated when the threads were
cut originally, rather than during welding?

The misalignment almost certainly had nothing to do with the welding,
IMHO, though I suppose it's possible that the shell was warped
somehow. I'm just betting the threads were cut wrong somehow -
probably by someone short-cutting (no pun intended) the process and
using two non-piloted taps.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Nate Knutson wrote:
In building up a Surly Long Haul Trucker for a friend, I encountered
this problem: The BB we used is a Shimano UN-73, with stock plastic
shoulderless left adapter cup. The left cup cracked during installation
while at less than final torque. I've eaten through plenty of left cups
now on this frame and they keep dying - one did it at very low torque,
I think even before the cup bottomed out on the BB. I currently have it
set up using a steel adapter cup off some other Shimano BB that seems
to work fine. While installing the steel one, it went in somewhat
rough, and I removed it and looked at the inside and there are gouges
where it was presumably rubbing against the BB. The bearing feels
signficantly less than perfect when everything is all tightened down.

What I'm guessing is going on is that the BB shell threads are out of
line with each other enough to cause all this. I don't see how a facing
error could cause this - could it?

I don't have access to piloted BB taps and am not familiar with using
them. My concern with chasing this frame's threads with piloted taps is
that if the error in the shell thread alignment is really bad, how
would just forcing piloted taps through it all work without ruining the
integrity of the threads? It seems like there's a judgement call here
that needs to be made with that, but I have no idea how to make it.

We can still warranty the frame but I really don't want to.

Yes there is a threading error.

BB shells are threaded before frame assembly. After welding there can be
significant curvature to the BB shell. That leaves the two sides'
threads not on one axis.

Yes a piloted tap set is _exactly_ what you need. The second component
is a skilled operator for those taps. And the appropriate (steel? Al?
ti? ) cutting fluid.


--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971