"Luke" a écrit dans le message de news:
...
In article , Paul Hobson
wrote:

Ok, so I "finished" the old Peugeot to fixie convert today. Truth be
told, I need a shorter bottom bracket spindle, but that'll come later
(after my next paycheck).

So, to adjust the chainline to pretty darn good, I used spacers with the
chainwheel on the inside of the spider. All in all, the chainline was
off by about 2 mm (I know...I know). I used old stack bolts from my
BMX bike, and they seemed to work fairly well. I had to turn them
around since the female end didn't fit through the spacers
(shoddier...it just gets shoddier).

Then, I'm taking it out on a test run to the center of campus and I'm
spinning pretty fast down a decent hill. PING! Two of the stack bolts
fly off. scary scary scary. I slam on my front brake (my buddy, from
now on) and sure enough...they're gone.

My theory is this: I didn't tighten them enough and with the spacers,
they really couldn't thread enough. Will normal new short stack bolts
be long enough to deal with the spacers that I need for now??? Should I
get double chainring stack bolts and put more spacers on until I get the
new BB spindle???


Here are few thoughts and observations.

On all of my cranks the chainring bolts engage enough of the nut so
that the bolt ends (threaded portion) are just shy of being flush with
the nut (as viewed from the inner side of the chainring). If your
chainring bolt/nut relation is similar, I'd hazard that enough of the
nut has been engaged by the bolt.

That said, I'm skeptical that your BMX (i.e., single chainring) stack
bolts, when used with chainring spacers, could properly engage enough
of the bolts' threads.

Relating to the subject, how much have you spaced your chainring to the
insider of the spider? The less distance the better as greater spacing
will tend to promote a shearing action (correct term?) on the chainring
bolts. Perhaps this, in conjunction with your reversal of the stack
bolts), and their used condition, may be behind the liberation of your
fasteners: Are the bolts actually loosening or is the lip of the nut
shearing off and the bolt pulling through the spider? This has happened
to me on occasion with aged, overtightened - and correctly orientated -
stack bolts.

I suggest you start from scratch. Get spacers that allow for the proper
orientation of the stack bolts
http://sheldonbrown.com/harris/singlespeed.html#cranks and dual
chainring stackbolts, then give it another try. Though this time,
consider avoiding racing down hills on the maiden test run!!

Luke

I assume you tightened each one a bit before proceeding to the next bolt to
tighten (not an adjacent one), until all were done?
Make sure you retighten the bolts after riding a bit.