dnfcx

So full sprint. Left pedal fell off. I took a beating. Helmet is cracked.

Anyhow

The pedal seemed to wind itself out. Any idea why this would happed? Maybe the pedal was not tightened down? Or cross threaded? The pedal is back on now, and the threads on the arm are a bit tough(required a bit of extra work to get the pedal in, but the pedal seems solid and tight now.



Sorry to ramble. Muscle relaxant making me loopy.

mtalinm

my entire left crank fell off on Monday, while I was commuting. threads were fine, so I reattached it. strangest thing I've yet seen

ptle

It's happen to me before (not while sprinting).

I think it's cause from improper pedal installation. Make sure you grease the pedal and torque it correctly.

CrimsonKarter21

+1

dnfcx

I was leaning toward a torque issue as well. Why would it spin out though? During the bottom and back stroke?

really shakes my confidence.

Tulex

Did you get 2 right hand cranks and pedals?

dnfcx

heh. no.

Time Atac XS on a Rival crankset.

cooker

Pedals screw in but they also rotate around their own axle on internal bearings. Those bearings inside the pedal actually apply a bit of torque to the axle as they roll, screwing it in tighter. If those bearings are gummed up and not rolling, it reverses the torque and unscrews the pedal. So make sure your pedals spin freely.

gsteinb

WTF. You should try to not do that. A pedal can not unwind itself.

dnfcx

if I pedal cant unwind itself - which is what I thought, could a cross thread cause the issue? Since then it would be more of a "force" issue to come out (sprint)?

Im really just looking for the why so I can make sure it does not happen again. THough in my 20 years it has never happened before.

gsteinb

Dunno. The threads go in the direction the crank turns. The only time I've ever seen one unwind was on a tandem with a kids adapter. On that the chainring is on the wrong side so you have to really torque down on the pedal.

gsteinb

What kind of pedals? Is it possible they were on backwards?

electrik

Square taper? Crankset is toast.. get out the loctite.

cooker

The pedal can unwind itself if the bearings inside it are jammed. The bearings normally roll as the pedal turns, applying torque that tightens the pedal into the crank. However if the bearings are not rolling, the torque is reversed and the pedal gets unscrewed.

scirocco

Have you still got the pedal and crank? If the pedal was cross-threaded the evidence will be there in the trashed threads on both. Cross-threading damage doesn't disappear with time.

Tulex

If you managed to get a cross threaded pedal all the way in to the shoulder, I don't think it is coming out.

grolby

Um, no. The force from the bearings is in the unscrewing direction on one side (the right) and tightening direction on the other (left). What causes the pedals to tighten up is precession - the pedal spindle actually wobbles in the threads. This is why the left-threaded left pedal (and left threaded fixed cup for the BB) were invented - bearing precession was unscrewing them. Not friction from bearings, which would actually seem to unscrew a right pedal, and tighten a left pedal.

It is physically impossible for bearing drag to unwind a left pedal; it would actually tend to have the OPPOSITE effect.

grolby

Some links:

https://www.sheldonbrown.com/brandt/left.html

https://www.sheldonbrown.com/gloss_p.html#precession

dcvelo

You should read the links in your succeeding post again...they're saying that the reason crank arms have reversed threads is to prevent precession. The concept behind the design is that if the bearings in the pedal spindle go south, the threads connecting the pedal to the crankarm unthread themselves. The alternative is transferring that force to your knee and ankles. Not a good scenario.

True for either side...because the threads on the pedal are reversed.

cooker

Since the left and right pedals turn in the opposite direction to each other, and have opposite thread, they behave exactly the same.

ahsposo 

So, how's your right testicle?

carpediemracing 

Tight pedals won't come out on their own. When I was taught how to build a bike, the guy told me that if I start installing a pedal, I should tighten it before I leave the bike, no matter why I need to leave the bike. He said that even if the Pope walked into the shop, I should tighten the pedal before I went to kiss his ring or whatever you're supposed to do when the Pope walks into your shop.

I think that whoever installed the pedal was never taught the Pope rule. Although intentions are good, it's pretty much a given that pedals that fall off weren't tightened enough to begin with.

I'd replace the left crank because some of the threads were damaged. It's not worth risking having the pedal get loose etc.

Ditto to whoever's crank fell off. Replace that arm - it's been compromised.

cdr

CrimsonKarter21

-Put the pedal back in
-Tighten it
-Do a few rides with a 15mm spanner, or a 6mm or 8mm allen
-Check pedal a few times throughout your ride
-Forget about the incident within a week when nothing goes wrong

colombo357

Your pedals screwed you over. Throw them away fast.

CrimsonKarter21

I see what you did there...