Crank square taper hole too large - options?

[Mark McMaster]

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 [email protected]

 

[Phil Holman]

"Mark McMaster" <[email protected]> wrote in message news:[email protected]...
> 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 [email protected]

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

 

[Dianne_1234]

Mark McMaster <[email protected]> wrote in message news:<[email protected]>...
> 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 [email protected]

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 <[email protected]>, dianne_ [email protected] says...
> Mark McMaster <[email protected]> wrote in message news:<[email protected]>...
> > 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 [email protected]
>
> 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 <[email protected]> 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...

---
My email address is antispammed; pull WEEDS if replying via e-mail.

Yes, I have a killfile. If I don't respond to something, it's also possible that I'm busy.

 

[A Muzi]

"Mark McMaster" <[email protected]> wrote in message news:[email protected]...
> 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 <[email protected]>, Mark McMaster <[email protected]> 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

 

[Shaun Rimmer]

Dan Brussee <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>, dianne_ [email protected] 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.

And yes, I've used beverage cans for this on 2 occasions without trouble, except for the one time I
made them too long, and the 'edge' protruding out the back of the crank arm cut the bearing seal all
to hell, heheheheh.....

Oh, be sure to not use soft drink cans - the metal must be from a beer can, and preferably a strong
beer at that, to work properly ',;~}~

Shaun aRe

 

[Dan Brussee]

In article <[email protected]>, [email protected] says...
>
> Dan Brussee <[email protected]> wrote in message
> news:[email protected]...
> > In article <[email protected]>, dianne_ [email protected] 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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[Shaun Rimmer]

Dan Brussee <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>, [email protected] says...
> >
> > Dan Brussee <[email protected]> wrote in message
> > news:[email protected]...
> > > In article <[email protected]>, dianne_ [email protected] 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.

If anyone could tell, it'd be almost the ultimate princess and the pea tale ',;~}~

Shaun aRe

 

[Andrew Webster]

"A Muzi" <[email protected]> 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" <[email protected]> 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 [email protected] Madison, WI 53711 USA
-----------------------------------------------

 

[Peter Cole]

"Andrew Webster" <[email protected]> wrote in message
news:[email protected]...
>
> 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.

Darn, I thought I was the only one that happened to. I once bought cranks that were 0 degrees apart.
How was I supposed to pedal that, by hopping? Jeesh!

 

[Jasper Janssen]

On Mon, 14 Jul 2003 17:35:03 -0500, Jim Adney <[email protected]> wrote:

>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

 

[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