Help. My self-extracting crank bolts spontaneously self-extract

Mark Hickey wrote:
30 foot/pounds IS a lot of torque, but it's what crank bolts are
supposed to be tightened to. That's almost impossible with a normal
hex wrench or T-handle tool.

That's a relief, actually; I'd always wondered if I was overtightening
them.
--
David Damerell Kill the tomato!

Art Harris wrote:
They're probably ruined. There is no way you can get enough torque
using a 6 mm allen key.

I don't see why not.

Practical observation; I've installed cranks with a 6mm allen key on which
I've then ridden thousand of miles without anything bad happening.

Theoretical basis; Mark Hickey says 30 foot-pounds. My 6mm allen key is
about 4" long, and I reckon I can lean on it with about half my body
weight.
--
David Damerell Kill the tomato!

David Damerell wrote:

Art Harris wrote:

They're probably ruined. There is no way you can get enough torque
using a 6 mm allen key.


I don't see why not.

Practical observation; I've installed cranks with a 6mm allen key on which
I've then ridden thousand of miles without anything bad happening.

Theoretical basis; Mark Hickey says 30 foot-pounds. My 6mm allen key is
about 4" long, and I reckon I can lean on it with about half my body
weight.

I haven't found it to be a problem either. I have a folding bike that
requires removal of the cranks for packing and it also uses the
self-extracting allen-head bolts. I've had them off a few dozen times for
trips without any problems getting sufficient torque with the supplied
allen wrench (mine is about 8" long to make it easier).

"Adam Rush" wrote in message
m...
And the same is true if they are splined cranks. People are not
accustomed to paying attention when mounting splined cranks because
the
old square-tapered cranks did not require any attention -- other
than to
make sure the arms were going in opposite directions. It is not
hard
to mismount a Shimano splined crank and ruin it. -- Jay Beattie.

I'm afraid I don't understand.

With a square taper BB, the crank arm has only one way of going on --
square peg into square hole. There is no chance of ruining the
interface during installation, assuming you do not torque to a million
foot-pounds or the parts do not match in the first place. With the
Shimano splined BB, there is a "pseudo-fit place" -- a place where the
splines on the BB do not match up with the channels on the inside of the
crank arm, but they feel like they do. The crank arms are basically in
the right orientation, and there is no giant red flag to tell you that
there is a problem. If you torque the crank bolts when the arm and BB
are in this place, you end up squashing the splines, and you get that
permanent loose fit thing going. You really have to look at the
interface to make sure you have the proper spline alignment before
installing and tightening the bolts. Because there is less of an
interference fit on a splined BB (hardly any) you also have to be
scrupulous about getting the bolts up to torque, which means making the
investment in the right hex socket for your torque wrench. -- Jay
Beattie.

David Damerell wrote:
Art Harris wrote:
They're probably ruined. There is no way you can get enough torque
using a 6 mm allen key.

They may not be if the crank taper is not damaged. If they are now
torqued down properly they may stay tight. Only way to find out is
(a) inspect the taper (b) try it. I've rescued cranks that came
loose only once, many times is probably worse.

I don't see why not.
Practical observation; I've installed cranks with a 6mm allen key on which
I've then ridden thousand of miles without anything bad happening.

This happens, but it's also an example of the NASA theory of failure
analysis: we did it before and nothing broke, so we'll keep doing it.
There is some margin for error for people who are light on equipment.
Heavy people, mashers, people who stand on the pedals a lot will
have more failures.

Theoretical basis; Mark Hickey says 30 foot-pounds. My 6mm allen key is
about 4" long, and I reckon I can lean on it with about half my body
weight.

NFW. 4" is way too short. You aren't actually applying the force at
the very end of the allen key handle, and you aren't really putting
half your weight on it. I recommend borrowing a torque wrench (or buy
a cheap beam-type one) and trying it. The crank doesn't reach a hard
stop like a nut and bolt and it is really surprising how much you have
to reef on a nominal 16" long torque wrench handle to reach 30 foot
pounds - I sometimes give up at 25 ft-lb, the lower end of the spec
range.

In article , says...
Hi:
I have a travel bike with S+S couplers and self-extracting crank bolts.
Recently, perhaps because of the cold weather, I have found that the cranks
keep loosening up. I tighten the bolts as much as I can using a 6 mm hex
wrench but the cranks start "clunking" after less than 10 miles of riding.
Can anybody suggest a way to stop the bolts from loosening themselves?

If your cranks aren't ruined, which is a distinct possibility, then the
fix is to _PROPERLY_ tighten the cranks. Using your average 6mm hex wrench
is not the right way to do it. Best way is to get a 3/8 drive 6mm hex bit
and use a torque wrench to tighten the bolt to approx. 30ft/lb. Then leave
it alone. Oops, almost forgot. Don't froget to grease the tapers before
you mount the cranks.
--------------
Alex

In article ,
says...

That's a relief, actually; I'd always wondered if I was overtightening
them.

It's hadr to overtighten them. A while back someone on this newsgroup
did an experiment with an old set of cranks to see if they could break
the cranks by overtightening them. He ended up breaking the bolt head
before the cranks were damaged.
-------------
Alex

Alex Rodriguez wrote:
In article , says...

Hi:
I have a travel bike with S+S couplers and self-extracting crank bolts.
Recently, perhaps because of the cold weather, I have found that the cranks
keep loosening up. I tighten the bolts as much as I can using a 6 mm hex
wrench but the cranks start "clunking" after less than 10 miles of riding.
Can anybody suggest a way to stop the bolts from loosening themselves?


If your cranks aren't ruined, which is a distinct possibility, then the
fix is to _PROPERLY_ tighten the cranks. Using your average 6mm hex wrench
is not the right way to do it. Best way is to get a 3/8 drive 6mm hex bit
and use a torque wrench to tighten the bolt to approx. 30ft/lb. Then leave
it alone. Oops, almost forgot. Don't froget to grease the tapers before
you mount the cranks.
--------------
Alex


An even better way is to use an 8mm hex bit, which fits the bolts on
modern Shimano and Campagnolo cranks much better than a 6mm bit.
Maybe the OP had some unusual crank that took a 6mm bit, but I
don't think that's big enough for the torque required.

Dave Lehnen

Alex Rodriguez wrote:

In article ,
says...

That's a relief, actually; I'd always wondered if I was overtightening
them.

It's hadr to overtighten them. A while back someone on this newsgroup
did an experiment with an old set of cranks to see if they could break
the cranks by overtightening them. He ended up breaking the bolt head
before the cranks were damaged.

That'll happen virtually every time. The only way to split a crank is
to repeatedly tighten it down. The specified torque is that which
will allow the crank to squirm *just* the right distance up the bottom
bracket spindle taper. As the crank moves up the taper, it
effectively "loosens" the crank bolt (though not nearly enough for it
to come loose, assuming it's been installed properly).

However, if you once again torque the bolt to 30 ft/lbs, it will
squirm up a bit further (too far), at which time you might be tempted
to "snug it up" again, ad infinitum until the crank splits.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

(JP) wrote:

I'm not saying it is impossible to ruin a crank by riding it with a
loose crank arm, I'm saying that I think it is a lot more difficult
than the impression you get from the experts here, and I'd guess that
a lot of people have been convinced that their cranks were ruined when
all they needed to do was torque them down properly. (Don't know about
splined cranks, though.)

The problem is that the BB spindle is very hard, and the aluminum
crank is very soft. If the crank rotates on the spindle, the taper
fit is no longer square, but very slightly "bowed" on each of the
flats. Once this happens to a large enough degree, there's nothing
that keeps the crankarms from squirming back and forth.

IF you catch and correct the loose bolt before the flats are
sufficiently damaged, the aluminum will deform enough to provide a
"square fit", and all is well with the world.

However, like it or not, most cranks that have been ridden any real
distance loose are ruined. Heavier, stronger riders will damage them
quicker, and will have less luck getting a marginal crank to stay put
once it's tightened. Lighter riders or those who spend very little
time out of the saddle will do much less damage to a loose crank, and
will have a better chance of successfully using a damaged crank.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame