Left crank nut won’t stay tight

meb said:

My left crank nut when adequately torqued loosens within 3 miles.

I suspect the crank taper may be worn large and likely needs arm
replacing and will probably at least try another crank arm to see if it
fixes the problem, but alternatively can a lockwasher avert this
loosening or will that create some unforeseen problem?

Or should I be expecting a BB problem with the nut style BB-arm
fastening?

It may be that the bore is worn and you're bottoming on the taper. You
should be able to eyeball that.

If the bore is sloppy, bottoming or not, you may be able to continue to
use it if you shim with aluminum can stock. If it doesn't work, left
cranks are cheap.

meb said:

My left crank nut when adequately torqued loosens within 3 miles.

I suspect the crank taper may be worn large and likely needs arm
replacing and will probably at least try another crank arm to see if it
fixes the problem, but alternatively can a lockwasher avert this
loosening or will that create some unforeseen problem?

Or should I be expecting a BB problem with the nut style BB-arm
fastening?

--
meb

First time it loosened, you probably deformed the crank arm to the
point where it will never stay tight. New crankarm, installed per
factory instructions, and it will stay tight.

meb said:

My left crank nut when adequately torqued loosens within 3 miles.

I suspect the crank taper may be worn large and likely needs arm
replacing and will probably at least try another crank arm to see if it
fixes the problem, but alternatively can a lockwasher avert this
loosening or will that create some unforeseen problem?

Or should I be expecting a BB problem with the nut style BB-arm
fastening?

If you slip the arm off and look at the aperture from the
spindle side, you'll see that the square opening is no
longer square.

It's even more obvious when you compare your new arm just
before installation. Grease the taper, the threads, the
fastener and torque to 50Kcm. It won't be a problem in the
future.

You cannot damage or change a hardened CrMo spindle with a
soft aluminum arm so don't worry about the spindle or the
bolt/nut.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Anonymous said:

My left crank nut when adequately torqued loosens within 3 miles.

Quoted message said:

I suspect the crank taper may be worn large and likely needs arm
replacing and will probably at least try another crank arm to see if
it fixes the problem, but alternatively can a lockwasher avert this
loosening or will that create some unforeseen problem?

Quoted message said:

Or should I be expecting a BB problem with the nut style BB-arm
fastening?

http://www.sheldonbrown.com/brandt/installing-cranks.html

[email hidden]

meb said:

My left crank nut when adequately torqued loosens within 3 miles.

What do you consider adequate?

Quoted message said:

I suspect the crank taper may be worn large and likely needs arm
replacing and will probably at least try another crank arm to see if it
fixes the problem, but alternatively can a lockwasher avert this
loosening or will that create some unforeseen problem?

If the crank is loosening it's certainly toast.

Quoted message said:

Or should I be expecting a BB problem with the nut style BB-arm
fastening?

No.

jeverett3<AT>earthlink<DOT>net http://home.earthlink.net/~jeverett3

quote='A Muzi'meb said:

My left crank nut when adequately torqued loosens within 3 miles.

I suspect the crank taper may be worn large and likely needs arm
replacing and will probably at least try another crank arm to see if it
fixes the problem, but alternatively can a lockwasher avert this
loosening or will that create some unforeseen problem?

Or should I be expecting a BB problem with the nut style BB-arm
fastening?

If you slip the arm off and look at the aperture from the
spindle side, you'll see that the square opening is no
longer square.

It's even more obvious when you compare your new arm just
before installation. Grease the taper, the threads, the
fastener and torque to 50Kcm. It won't be a problem in the
future.

You cannot damage or change a hardened CrMo spindle with a
soft aluminum arm so don't worry about the spindle or the
bolt/nut.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971[/QUOTE]

Yep- a rhombus!

quote='Peter Cole'meb said:

My left crank nut when adequately torqued loosens within 3 miles.

I suspect the crank taper may be worn large and likely needs arm
replacing and will probably at least try another crank arm to see if it
fixes the problem, but alternatively can a lockwasher avert this
loosening or will that create some unforeseen problem?

Or should I be expecting a BB problem with the nut style BB-arm
fastening?

It may be that the bore is worn and you're bottoming on the taper. You
should be able to eyeball that.

If the bore is sloppy, bottoming or not, you may be able to continue to
use it if you shim with aluminum can stock. If it doesn't work, left
cranks are cheap.[/QUOTE]

Gave the shim a try. Would stay on about 6-8 miles before loosening a few times, beu degenerated to coming loose every 1 1/2-2 miles. Tried coupling the spline idea with the lockwasher, but the arm within a mile went into the BB and the crank arm motion unscrewed the BB out one end of the shell.

I'll replace it next month, I've depleted the 170mm left crank reserve supply, besides the roads I commute to work on after April's office move are too rough for an aluminum road bike. A Noticable improvement on a steel road bike today.