"pixelbrainz" <
[email protected]> wrote in message
news:[email protected]...
> I need the voice of an experienced wrench and it will be much appreciated.
>
> This has been flogged to death I know, but there is some very confusing information floating
> around and I have already paid the price so to speak. I have never mounted a splined crank and am
> a little confused.
>
> However, I have mounted many a tapered crank without any problem ever. I would very, very lightly
> grease the taper and gently tap the crankarm on with a rubber mallet. Then set the bolt around 80
> ftlbs or so, not using the bolt to force the arm on but as a retainer.
>
> Shimano specifies 430 inch pounds (greased) for the torque bolt on a
splined
> Ultegra crank. This is not a lot of tightening. However, when I removed the crank bolts, (on since
> new) they were so tight I thought I would break my allen wrench before the bolt let go. I had to
> use a 1" combo wrench as
a
> cheater. As a matter of fact I destroyed one crankarm, had to heat it to get it off.
>
> I notice that there is a bit of shaved and distorted area now where the crank was forced over the
> splines. Is normal? Once this occurs, do I need to change the torque?
>
> I have read to use everything ranging from 430 inlbs as specified to using an impact wrench. What
> is the acceptable norm for you wrenches out
there?
> I can't believe an impact wrench would be acceptable.
When you use a "one-key-release" or "Autex" type allen bolt crank removal system, add oil or grease
inside the cap in addition to the bolt's threads. The force of removal is borne against the inside
lip of the crank cover. A dry bolt doesn't turn easily.
Factories use impact wrenches because they are faster. Some days those wrenches are set high and
some days they are set low. This is below the threshhold of anyone's attention in a bicycle factory.
Let's review the literature: SR-Sakae said 350~400Kcm for a nutted spindle, 200~250Kcm for a
bolted one.
Shimano precisely says 34.3~44.1 Nm and converts that to 305~391inch pounds ( gotta love that "point
one") for regular cranks and 35~50Nm ( 305~435 in) for hollow arms. (Interestingly, they convert
34.3 and 35 Nm both to 305 inches, so you have to wonder about those decimal points)
The oldest crank torque rating I could find is Shimano's 1982 DuraAce Ex (with One Key Release) at
250~350Kcm Their original OctaJoint splined spindle on the Adamas was rated at 300~450Kcm with 14mm
bolts and at 250~350 _for the same arm and spindle_ with One KeyRelease.
Campagnolo currently says 32~38 Nm and 23.6~28 foot pounds (283.2~336 inches). (I never saw a
printed torque rating for crank bolts before about 1980 or so. Campagnolo didn't print a rating
until about 1990)
My impression of all that is that, unlike auto torque recommendations, these numbers seem
capricious, uselessly "precise" yet broad and probably pulled out of thin air. You have to wonder
about a number that's taken to a decimal point with a range of 30%! And when I see the same part
assembled with a 30% change in torque when the _fastener head_ is different, I can't take that
number seriously.
I torque cranks a bit higher than the printed spec because I used to find the occasional loose crank
at printed ratings. Like you, I am in the upper end of the range or slightly past. But I torque to
50Nm or so. You do realize that your 80lbs is double Shimano's rating, right? Lubricating fasteners
means you are transmitting more useful force to the work than you would on a dry thread.
I don't think your "tap with mallet" operation does anything useful. What do you mean by "not using
the bolt to force the arm on but as a retainer"? Are you smacking that arm hard enough to be the
equivalent of 80lbs? I bet not.
When you postulate "thought I would break my allen wrench before the bolt let go" , you should put a
bolt into a scrap spindle in a vise and torque it until something breaks. It takes a lot more than
you think. I once had a mechanic who did break off crank bolt heads but she was stronger than most
people and stopped that after we showed her a torque wrench. It's in the 200+lb range, off the end
of our scale. And the bolt will break before your wrench at any rate.
When you heated the crank you may have changed the crank material. I don't know how hot that was.
But the "shaved" may have been from not quite being lined up when the crank was installed. That's
all too easy with the current Shimano splined system. And that's why we remove the OneKey system
when we install those arms. You just can't easily tell it is on right otherwise.
So in my opinion you had difficulty removing the crank due to a dry crank bolt and cover and should
probably just reinstall the arm with lubricated fasteners (including the cover plates) and not
worry about it.
Shimano suggests lubricating the spline on these arms. (With square taper cranks we're dancing with
the Subject Whose Name Shall Not Be Spoken [or posted]) Damage to cranks is less likely due to
torque absolutely than to repeated installation/removal.
--
Andrew Muzi
http://www.yellowjersey.org Open every day since 1 April 1971
