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Re: am I ruining my crank?
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Peter Cole
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Aug 07, 2006 10:33 PDT
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Alan Abrams wrote:
| | Now, I was feeling quite proud of myself. I had just successfully
replaced both the inner chain ring (I had broken a tooth on the old
one) and the cogset (these both constituted bike maintenance jobs far
beyond anything I had attempted before). And, now I was out on the
road and the bike felt great (and _I_ felt great!). But then I started
to notice the chain was rubbing on the front derailleur when I was on
the big ring and the smallest cogs.
No big deal, I thought at first; I just need a minor limit screw
adjustment. But, then I started to wonder -- is it possible the reason
it's rubbing all of a sudden is that the crankset is not _quite_ as
far down on axle as it was before? And, further, could that mean that
I didn't tighten the crank bolt enough (and that I might be ruining
the crankset and/or axle)?
I don't have access to a torque wrench so I just followed Leonard
Zinn's counsel to make the crank bolt "snug" but "not to muscle it"
(and just tried to remember how tight it was when I took it off).
Anyway, any advice would be welcome. If it's just normal to maybe have
to adjust the front derailleur a little bit after removing (and
reinstalling) the (same) crankset, I'd sleep a little easier at night.
. . . And, yes, I _am_ going to ask around more to see if I can find a
torque wrench! :)
Be well.
--Alan
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There is little danger in over-tightening crank bolts, but the opposite
-- under-tightening -- can do this easily. For this reason I tighten
crank bolts *damn* tight. The Shimano spec says ~300 in-lb minimum.
That's a pretty fair amount of torque. I don't use a torque wrench
myself, for crank bolts I use a standard Allen wrench with a (perhaps 1
foot) length of 1/2" pipe as an extender. I grease the spindle and
*never* re-tighten. I have never had a crank come loose on any of the
dozen or so bikes I maintain. If done correctly there is nothing to fear
from repeated crank removals.
If you have any doubt that you may have under-tightened, my advice would
be to loosen the cranks completely (with an extractor), then grease and
re-tighten. If you're in doubt about what 300 in-lb feels like then
perhaps you should invest in a torque wrench -- otherwise err on the
side of caution and over-tighten a bit.
As others have pointed out, it's much more likely to have a left crank
loosen, since most of the right crank force never makes it to the
spindle, being taken up by the chain -- so your fears are probably
groundless -- but, OTOH, cranks are pretty expensive...
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