Re: Crank square taper hole too large - options?

[Phil Holman]

"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

[Werehatrack]

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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[dianne_1234]

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!

[Dan Brussee]

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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[Peter]

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.

[Werehatrack]

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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[A Muzi]

"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

[Paul Southworth]

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

[Doug Milliken]

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.

[Dan Brussee]

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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[Andrew Webster]

"A Muzi" > wrote in message
<cut>
> 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.

FWIW...a word of caution, it may be worthwhile taking the old example
with you. I bought a new left crank three or four years ago. Fitted
it only to find that the left and right cranks were only 90 degrees
apart instead of 180.

Andrew Webster

[Jim Adney]

On Sun, 13 Jul 2003 15:42:36 GMT "Phil Holman" >
wrote:

>Use the top of a food can. Cut a rectangle and bend it at 90 degrees to
>contact two of the four flats.

I work with a fellow who did exactly this with a piece of alum can
several years ago. He's an amazingly strong rider and has had no
problems with it over the years. I had my doubts, but his experience
is a better data point than my concern.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

[Ted Bennett]

> >I work with a fellow who did exactly this with a piece of alum can
> >several years ago. He's an amazingly strong rider and has had no
> >problems with it over the years. I had my doubts, but his experience
> >is a better data point than my concern.
>
> Given that in most cases we're talking about aluminium cranks and square
> holes, I'd have a really hard time figuring the aluminium cans to be of
> not strong enough material. Might want to make sure the coke is thoroughly
> not on there any more though, what with the urban legend concerning coke's
> corrosiveness. The only possible issue with coke can shims I can see is in
> situations with significant (flex) movement wearing through the shims --
> but that flex would wear away the crank hole anyway, as I'm sure all of us
> has seen at one point or another when a crankbolt happened to be
> less-than-optimally torqued.
>
> Jasper

For further proof of the corrosiveness of coke, read any of the assorted
"thoughts" of Gene Daniels, otherwise known as "datakoll".

--
Ted Bennett
Portland OR