Crank square taper hole too large - options?

"Mark McMaster" wrote in message
...
I have a set of unused cranks for square taper BB.
Unfortunately, it appears that the tapered hole on the left
crank is a bit on the large side - I've tried mounting it on
several BB spindles, but the bolt bottoms out on the end of
the spindle just before reaching full torque (25 ft-lb).
The square taper hole appears to be undamaged and otherwise
functional - it's just a little too large.

Clearly this is not a good situation. While the practical
solution is to get a different set of cranks, I really
wanted to use these particular cranks (Grafton SpeedStix) on
a special "project" bike. So what are my options?

The dimension across the outboard end of the square hole is
12.38 mm. Are there any brands of BB's that have tapered
flats particularly wider than others that might work?

Two other options that have occurred to me are to grind down
the end of a BB spindle a few millimeters to keep the bolt
from bottoming on the end of the spindle. There seems to be
plenty of room between the crank and the root of the flats,
so that the crank won't bottom at the end of the taper. Any
liabilities to trying this out?

Another option might be to use a thin shim between the crank
and spindle. The most easily accessible source of material
to make a shim is an aluminum beverage can. But would this
metal be too soft for the stresses in this joint? Would
steel shim stock be preferable?

Thanks in advance for any suggestions or experiences shared.


Mark McMaster


Use the top of a food can. Cut a rectangle and bend it at 90 degrees to
contact two of the four flats. I've done this on my training bike and
haven't had any problems for 1000s of miles. If like you say the crank
is not bottoming out into the radius, then you could put a washer/spacer
under the head of the bolt that would allow the crank spindle to
protrude further through the crank. Aluminum is not recommended.

Phil Holman

It sounds like the hole is a bit too large. My first thought would
have been to whittle a steel spacer washer to go in the recess, with a
square hole a bit larger than the end of the BB shaft, to allow the
shaft to come through far enough to torque the bolt properly. (I've
had to create similar things to fix industrial equipment and
automotive racing gear once in a while.) These might actually already
exist; you might check with the lbs to see if they've heard of the
problem, and see what they recommend. If I had tried it, I'd have
done it as a two-step process, installing the crank and bottoming it,
and then adding the collar. As long as there's adequate clearance
between the back of the arm and the BB, I can't see where this would
cause a problem. If you try this trick, it might be wise to put a
couple of *small* drops of gap-filling superglue behind the collar to
keep it in place.

By the way, while shimming might work as a temporary or emergency fix,
I'd consider it a kluge myself. It would be a bugger to keep the
shims in position while assembling, and with the extra sliding surface
involved, the torquing would certainly not be as accurate a measure of
installation force as it should be.

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Mark McMaster wrote in message ...
I have a set of unused cranks for square taper BB.
Unfortunately, it appears that the tapered hole on the left
crank is a bit on the large side - I've tried mounting it on
several BB spindles, but the bolt bottoms out on the end of
the spindle just before reaching full torque (25 ft-lb).
The square taper hole appears to be undamaged and otherwise
functional - it's just a little too large.

Clearly this is not a good situation. While the practical
solution is to get a different set of cranks, I really
wanted to use these particular cranks (Grafton SpeedStix) on
a special "project" bike. So what are my options?

The dimension across the outboard end of the square hole is
12.38 mm. Are there any brands of BB's that have tapered
flats particularly wider than others that might work?

Two other options that have occurred to me are to grind down
the end of a BB spindle a few millimeters to keep the bolt
from bottoming on the end of the spindle. There seems to be
plenty of room between the crank and the root of the flats,
so that the crank won't bottom at the end of the taper. Any
liabilities to trying this out?

Another option might be to use a thin shim between the crank
and spindle. The most easily accessible source of material
to make a shim is an aluminum beverage can. But would this
metal be too soft for the stresses in this joint? Would
steel shim stock be preferable?

Thanks in advance for any suggestions or experiences shared.


Mark McMaster


I can't think of any reason grinding the spindle shorter would be
dangerous.

I've used coke can shim on crank tapers on three or four different
cranks. The "chainline" effect I measured was about 2.5 mm, IIRC.
That's wrapped around all four flats. I torqued to 25 foot pounds. The
excess shim scrunches up (either outboard or inboard), but I
experienced no functional problems. I even re-used the same shim after
overhaul. I took that opportunity to trim away the ugly excess.

Someone else suggested wrapping over just two flats. I imagine this
might be easier than wrapping over all four, and guess it might give
you 1 mm or so.

You'll probably hear from people who've cracked those cranks. I've
seen several.

Let us know what works!

In article , dianne_
says...
Mark McMaster wrote in message ...
I have a set of unused cranks for square taper BB.
Unfortunately, it appears that the tapered hole on the left
crank is a bit on the large side - I've tried mounting it on
several BB spindles, but the bolt bottoms out on the end of
the spindle just before reaching full torque (25 ft-lb).
The square taper hole appears to be undamaged and otherwise
functional - it's just a little too large.

Clearly this is not a good situation. While the practical
solution is to get a different set of cranks, I really
wanted to use these particular cranks (Grafton SpeedStix) on
a special "project" bike. So what are my options?

The dimension across the outboard end of the square hole is
12.38 mm. Are there any brands of BB's that have tapered
flats particularly wider than others that might work?

Two other options that have occurred to me are to grind down
the end of a BB spindle a few millimeters to keep the bolt
from bottoming on the end of the spindle. There seems to be
plenty of room between the crank and the root of the flats,
so that the crank won't bottom at the end of the taper. Any
liabilities to trying this out?

Another option might be to use a thin shim between the crank
and spindle. The most easily accessible source of material
to make a shim is an aluminum beverage can. But would this
metal be too soft for the stresses in this joint? Would
steel shim stock be preferable?

Thanks in advance for any suggestions or experiences shared.


Mark McMaster


I can't think of any reason grinding the spindle shorter would be
dangerous.

I've used coke can shim on crank tapers on three or four different
cranks. The "chainline" effect I measured was about 2.5 mm, IIRC.
That's wrapped around all four flats. I torqued to 25 foot pounds. The
excess shim scrunches up (either outboard or inboard), but I
experienced no functional problems. I even re-used the same shim after
overhaul. I took that opportunity to trim away the ugly excess.

Someone else suggested wrapping over just two flats. I imagine this
might be easier than wrapping over all four, and guess it might give
you 1 mm or so.

I would think that 2 flats and 4 flats would yield the same chainline
offset. 4 flats would just give 4 times the contact area. If the shim
does not compress, then 2 flats would not be used at all... not good.

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Werehatrack wrote:

By the way, while shimming might work as a temporary or emergency fix,
I'd consider it a kluge myself. It would be a bugger to keep the
shims in position while assembling, and with the extra sliding surface
involved, the torquing would certainly not be as accurate a measure of
installation force as it should be.

The leftside stoker's crank on our tandem requires a shim to
prevent it from going on so far that the chainwheel bolts hit the
lockring on the BB. Aluminum foil on the square taper is
sufficient to allow the crank to be properly tightened without
hitting the lockring. It may be a kluge but it has worked well
for the last 25 years and I see no reason why it won't work for
another 25.

On Sun, 13 Jul 2003 21:59:16 GMT, Peter may have
said:

Werehatrack wrote:

By the way, while shimming might work as a temporary or emergency fix,
I'd consider it a kluge myself. It would be a bugger to keep the
shims in position while assembling, and with the extra sliding surface
involved, the torquing would certainly not be as accurate a measure of
installation force as it should be.

The leftside stoker's crank on our tandem requires a shim to
prevent it from going on so far that the chainwheel bolts hit the
lockring on the BB. Aluminum foil on the square taper is
sufficient to allow the crank to be properly tightened without
hitting the lockring. It may be a kluge but it has worked well
for the last 25 years and I see no reason why it won't work for
another 25.

Experience after the fact is always the best predictor of success...

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"Mark McMaster" wrote in message
...
I have a set of unused cranks for square taper BB.
Unfortunately, it appears that the tapered hole on the left
crank is a bit on the large side - I've tried mounting it on
several BB spindles, but the bolt bottoms out on the end of
the spindle just before reaching full torque (25 ft-lb).
The square taper hole appears to be undamaged and otherwise
functional - it's just a little too large.

Clearly this is not a good situation. While the practical
solution is to get a different set of cranks, I really
wanted to use these particular cranks (Grafton SpeedStix) on
a special "project" bike. So what are my options?

The dimension across the outboard end of the square hole is
12.38 mm. Are there any brands of BB's that have tapered
flats particularly wider than others that might work?

Two other options that have occurred to me are to grind down
the end of a BB spindle a few millimeters to keep the bolt
from bottoming on the end of the spindle. There seems to be
plenty of room between the crank and the root of the flats,
so that the crank won't bottom at the end of the taper. Any
liabilities to trying this out?

Another option might be to use a thin shim between the crank
and spindle. The most easily accessible source of material
to make a shim is an aluminum beverage can. But would this
metal be too soft for the stresses in this joint? Would
steel shim stock be preferable?

Thanks in advance for any suggestions or experiences shared.

Since lefts fail much more frequently than rights, any LBS which services
bicycles will have a selection of left arms. We buy them in tens. Although
it may not be aesthetically identical pretty much any arm the same length
will do, usually under $20.

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

In article ,
Mark McMaster wrote:
I have a set of unused cranks for square taper BB.
Unfortunately, it appears that the tapered hole on the left
crank is a bit on the large side - I've tried mounting it on
several BB spindles, but the bolt bottoms out on the end of
the spindle just before reaching full torque (25 ft-lb).
The square taper hole appears to be undamaged and otherwise
functional - it's just a little too large.

Clearly this is not a good situation. While the practical
solution is to get a different set of cranks, I really
wanted to use these particular cranks (Grafton SpeedStix) on
a special "project" bike. So what are my options?

The dimension across the outboard end of the square hole is
12.38 mm. Are there any brands of BB's that have tapered
flats particularly wider than others that might work?

Probably not enough to matter.

Two other options that have occurred to me are to grind down
the end of a BB spindle a few millimeters to keep the bolt
from bottoming on the end of the spindle. There seems to be
plenty of room between the crank and the root of the flats,
so that the crank won't bottom at the end of the taper. Any
liabilities to trying this out?

Sounds OK to me but if the crank really bottoms out at the end
of the taper then it's not going to stay tight no matter how
tight that bolt is.

Another option might be to use a thin shim between the crank
and spindle. The most easily accessible source of material
to make a shim is an aluminum beverage can. But would this
metal be too soft for the stresses in this joint? Would
steel shim stock be preferable?

You're just going to have to try it and see if you can get it to
stay tight. If aluminum is too soft I would pick copper next.

--Paul

On Sun, 13 Jul 2003, Phil Holman wrote:

"Mark McMaster" wrote in message
...
I have a set of unused cranks for square taper BB.
Unfortunately, it appears that the tapered hole on the left
crank is a bit on the large side - I've tried mounting it on

Use the top of a food can. Cut a rectangle and bend it at 90 degrees to
contact two of the four flats. I've done this on my training bike and

I used some 0.007 inch steel shim stock I had around, cut a piece to fit
over 2 faces as above--works fine. I did the trig in advance to see what
thickness shim was required. The actual distance that the arm moved along
the taper matched the calculation quite well.

In article ,
says...

Dan Brussee wrote in message
...
In article , dianne_
says...

Someone else suggested wrapping over just two flats. I imagine this
might be easier than wrapping over all four, and guess it might give
you 1 mm or so.

I would think that 2 flats and 4 flats would yield the same chainline
offset. 4 flats would just give 4 times the contact area. If the shim
does not compress, then 2 flats would not be used at all... not good.

They were talking about 2 _adjacent_ flats, not 2 opposite ones - all 4
sides contact.


I see. Very small consideration, but that would make a very slign
excentric. Probably not even noticable though.

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