partially /almost fully stripped crank arm.

[Selvam]

Hello folks,

I  had replaced the pedal in my bike, when i tried putting the original pedal back, it refused to tighten. when i removed the pedal, i noticed the threads in the pedals are partially stripped. i was really careful not to cross thread the pedal. any solution to fix this other than replacing the crank arm/ crank set?

[Opendro]

Threads on the pedal are damaged or the threads in the crank arm? I still find it hard to believe that they could be damaged. The pitch of threads on the pedal are pretty large. Anyway, if you have damaged on the crank arm, you have to replace it.

If it is on the drivetrain side and MTB/hybrid, they come with forged riveted chain rings and they need to be replaced together. If in road bike, only the arm (with spiders if on drive side) need to be replaced. You can try some shops for any discarded arms. Else, new one is the only option.

[Prashanth Chengi]

Can you elaborate on 'refused to tighten'? Let's get the rookie question out of the way, so which pedal is it? The right side or the left? You do know that the pedal on the left side is reverse threaded, right? You have to turn it anti-clockwise, to tighten it. 

/Prashanth

On Wed, Aug 31, 2016 at 6:54 PM, Selvam <thanga...@gmail.com> wrote:

Hello folks,

I  had replaced the pedal in my bike, when i tried putting the original pedal back, it refused to tighten. when i removed the pedal, i noticed the threads in the pedals are partially stripped. i was really careful not to cross thread the pedal. any solution to fix this other than replacing the crank arm/ crank set?

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[Thangaselvam Muthusamy]

Correct. It's on the left side, non drive train side, I also am aware of the threading, I used another pedal as the reference.
When I said it refused to tighten, I meant it keeps rotating free never gets tight initial couple of turns would feel fine and then later it gets loose and floopy about the threads. I could see that the threads on the far side of the crank is stripped.

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[Pradeep Naidu]

I faced the same issue with my polygon Zenith, the crank arm thread was ate up by the pedal.
Had to change the whole crank set. I'm running on the fyxation crank now.
It's very possible Oppen.

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[Prashanth Chengi]

Always use some grease on the pedal, before screwing it on. Hand-tighten carefully, to ensure that it doesn't cross thread, and then, give a firm twist with a spanner. You really don't need to tighten the pedals too much, as they tighten when you ride. Even will all of these precautions, if the threads get eaten up, they must be of really poor quality in the first place, so yes, a replacement with a good quality crank arm will not only fix the problem, but also keep it from reoccuring.

/Prashanth

[Opendro]

Pedals don't tighten when you ride. It is the other way. If your pedal bearing balls get jammed, riding would loosen up the pedals. Designers did this way as they considered tightening on working bench using freewheeling (without rotating rear wheel) as more preferred. Moreover, they didn't really assume that pedal bearing balls would jam ;-P

On Thursday, September 1, 2016 at 3:21:30 PM UTC+5:30, Prashanth Chengi wrote:

Always use some grease on the pedal, before screwing it on. Hand-tighten carefully, to ensure that it doesn't cross thread, and then, give a firm twist with a spanner. You really don't need to tighten the pedals too much, as they tighten when you ride. Even will all of these precautions, if the threads get eaten up, they must be of really poor quality in the first place, so yes, a replacement with a good quality crank arm will not only fix the problem, but also keep it from reoccuring.

/Prashanth

On Thu, Sep 1, 2016 at 11:27 AM, Pradeep Naidu <pradee...@gmail.com> wrote:

I faced the same issue with my polygon Zenith, the crank arm thread was ate up by the pedal.
Had to change the whole crank set. I'm running on the fyxation crank now.
It's very possible Oppen.

On 01-Sep-2016 2:40 PM, "Thangaselvam Muthusamy" <thanga...@gmail.com> wrote:

Correct. It's on the left side, non drive train side, I also am aware of the threading, I used another pedal as the reference.
When I said it refused to tighten, I meant it keeps rotating free never gets tight initial couple of turns would feel fine and then later it gets loose and floopy about the threads. I could see that the threads on the far side of the crank is stripped.

On Thu 1 Sep, 2016, 2:29 PM Prashanth Chengi, <prashant...@gmail.com> wrote:

Can you elaborate on 'refused to tighten'? Let's get the rookie question out of the way, so which pedal is it? The right side or the left? You do know that the pedal on the left side is reverse threaded, right? You have to turn it anti-clockwise, to tighten it. 

/Prashanth

On Wed, Aug 31, 2016 at 6:54 PM, Selvam <thanga...@gmail.com> wrote:

Hello folks,

I  had replaced the pedal in my bike, when i tried putting the original pedal back, it refused to tighten. when i removed the pedal, i noticed the threads in the pedals are partially stripped. i was really careful not to cross thread the pedal. any solution to fix this other than replacing the crank arm/ crank set?

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[Opendro]

Having said that, I agree, you never have to tighten a pedal so much that you would need a long levered spanner next time to open it.

[Prashanth Chengi]

Quoting Sheldon Brown below: (I'm not calling Open an armchair engineer!)

"Another popular theory of armchair engineers is that the threads are done this way so that, if the pedal bearing locks up, the pedal will unscrew itself instead of breaking the rider's ankle.

The left-threaded left pedal was not the result of armchair theorizing, it was a solution to a real problem: people's left pedals kept unscrewing!

That said, I was wrong about the pedal tightening while pedalling. What I meant was that it doesn't loosen up, while riding, so if you have tightened it reasonably, it won't come loose by pedalling, so extreme tightening is simply not required. 

/Prashanth

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[Opendro]

That is totally wrong. You try jamming the bearings of the left pedal. It will definitely unscrew with the left-threading.

Thinking of which, even the bottom brackets would unscrew while riding if we jammed the bearing balls. So, it may be deliberatly to unscrew on ride rather than solving the unscrewing.

[Prashanth Chengi]

Open, what you say is true, but that's not the reason for the reverse-thread. The simple reason for the reversed-thread is that even with perfectly functional bearings, the left pedal would have simply come unscrewed, on pedalling.

/Prashanth

[Opendro]

But it does not come unscrewed on pedaling as we know. Did I miss something? Ah. Having said that I have seen pedals coming off during races. One such was in BBCh race Criterium in Bhartiar City - one team member of Specialized Kynkyny had the pedal fallen off. That is why I like tinkering a bit on my pedals bearing so as to spin smoothly, i.e. when tapped with a finger, the pedal should spin at least a few rotations. The penalty sometimes is a worn out cup of course as all the balls may not get simultaneous contact sometimes. Over time, I have learnt to make it perfect.

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[Opendro]

Anyway, my point is that if the intention was to prevent unscrewing during pedaling, the engineers have miserably failed as it will only do the opposite :-)

[Prashanth Chengi]

"It doesn't come unscrewed, on pedalling,  as we know". Yes, this is because it's reverse threaded! Get a custom crank arm made which regular threading (you won't find one like that on any bike, hence custom made) , and you'll be able to see if it unscrews or not. My take, as well as  Sheldon Brown's, is that it will indeed come unscrewed.  Why is this hard to understand? In fact, do this: just install the pedal and don't even finish fully hand-tightening it, ie it should be loose and spin easily. Use a cleated shoe, clip in and start pedalling. You'll see that it the pedal will tighten. Once it's reasonably tight, the applied torque will translate to the chain rings, without further tightening the pedal, but when it's loose, it first tightens the pedal. It's super easy to check it out. You could do it right now and see for yourself.  No, the engineers haven't failed. 

/Prashanth

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[Ashok Kumar S]

http://physics.stackexchange.com/questions/6488/why-are-bicycle-pedal-threads-handedness-left-on-the-left-and-right-on-the-righ

Thanks and regards,

Ashok

Sent from my iPhone

[Opendro]

Now my turn to ask : Why is it so hard to understand?

Even the link below has got it wrong. Guys, why do you always blindly believe what is written on the internet. This is such a simple thing to test. Please go home and do it.

For myself, I'm indeed an arm chair engineer, that is because I can imagine and visualize things pretty well without getting hands dirty ;) I'm out.

[Yateesh Kumar]

Do you have pics?

On 31-Aug-2016 22:24, "Selvam" <thanga...@gmail.com> wrote:

Hello folks,

I  had replaced the pedal in my bike, when i tried putting the original pedal back, it refused to tighten. when i removed the pedal, i noticed the threads in the pedals are partially stripped. i was really careful not to cross thread the pedal. any solution to fix this other than replacing the crank arm/ crank set?

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[Thangaselvam Muthusamy]

I'll click and send soon.

On Thu 1 Sep, 2016, 10:17 PM Yateesh Kumar, <kumar....@gmail.com> wrote:

Do you have pics?

On 31-Aug-2016 22:24, "Selvam" <thanga...@gmail.com> wrote:

Hello folks,

I  had replaced the pedal in my bike, when i tried putting the original pedal back, it refused to tighten. when i removed the pedal, i noticed the threads in the pedals are partially stripped. i was really careful not to cross thread the pedal. any solution to fix this other than replacing the crank arm/ crank set?

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[Puneet Rai]

Guys, the technicality of it is not a big deal.
The direction in which the bottom bracket turns is the same direction in which the pedal must be tightened - i.e. if you're on the left side, the BB is turning counter clockwise, hence the pedal must be tightened in a CCW direction. The reverse is true when you stand on the right side. Hence, after the pedals are tightened, a downward stroke of the pedals has the effect of further tightening the pedals to the crank arm.
However, if you have a left crank arm with a normal direction thread and a right crank arm with a reverse thread, a downward stroke will do the reverse, it will direct energy to loosening the pedal, not immediately but over some time.
So Prashant, in my view, your conclusion was right.

On another completely disconnected note, think about the threading of your humble kitchen blender blade and the direction of the threading of the rubber coupler of the jar that mates with the motor. Food for thought, in more ways than one :)

Puneet

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[Opendro]

Again wrong. This is what I sent to Prashanth individually. Either try to visualize it or play on the real pedal. Pedaling (riding) has a tendency to unscrew both the pedals and both the sides of bottom bracket. Period. Freewheel/cassette is the opposite, i.e. it will tighten on riding.

Please try this. Put the cycle on a stand so that you can pedal forward or drop the chain so that you don't have to really ride while pedaling forward.

Now, hold the spindle (where the spanner would lock) with your fingers. Pedal forward. See what happens.

Let me explain for the right arm first.

Assume the arm is at 3 O clock position with your right foot sole horizontal to the ground, i.e. your shoe is parallel to the arm. Now, move to 6 O clock position. If the spindle bearing balls were jammed, either of the two things will happen:

1. Either your shoe will still remain parallel to the arm, i.e. perpendicular to the ground now (with toe pointing down), or
2. Spindle should turn counter clockwise by 90 degrees for the shoe to remain horizontal to the ground.

As we know, counter clockwise turn of the spindle means unscrewing for the right pedal.

On Thursday, September 1, 2016 at 11:37:07 PM UTC+5:30, Veloracle wrote:

Guys, the technicality of it is not a big deal.
The direction in which the bottom bracket turns is the same direction in which the pedal must be tightened - i.e. if you're on the left side, the BB is turning counter clockwise, hence the pedal must be tightened in a CCW direction. The reverse is true when you stand on the right side. Hence, after the pedals are tightened, a downward stroke of the pedals has the effect of further tightening the pedals to the crank arm.
However, if you have a left crank arm with a normal direction thread and a right crank arm with a reverse thread, a downward stroke will do the reverse, it will direct energy to loosening the pedal, not immediately but over some time.
So Prashant, in my view, your conclusion was right.

On another completely disconnected note, think about the threading of your humble kitchen blender blade and the direction of the threading of the rubber coupler of the jar that mates with the motor. Food for thought, in more ways than one :)

Puneet

On Sep 1, 2016 10:18 PM, "Thangaselvam Muthusamy" <thanga...@gmail.com> wrote:

I'll click and send soon.

On Thu 1 Sep, 2016, 10:17 PM Yateesh Kumar, <kumar....@gmail.com> wrote:

Do you have pics?

On 31-Aug-2016 22:24, "Selvam" <thanga...@gmail.com> wrote:

Hello folks,

I  had replaced the pedal in my bike, when i tried putting the original pedal back, it refused to tighten. when i removed the pedal, i noticed the threads in the pedals are partially stripped. i was really careful not to cross thread the pedal. any solution to fix this other than replacing the crank arm/ crank set?

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[Ashok Kumar S]

Open,

The link i shared earlier was talking about your point and also it had given the reason why the pedal gets tightened and not loosened which is counter intuitive. They attribute it to mechanical precession. Honestly, I had not learned this in any of my physics classes and is new to me.

https://en.wikipedia.org/wiki/Precession_%28mechanical%29
http://physics.stackexchange.com/questions/6488/why-are-bicycle-pedal-threads-handedness-left-on-the-left-and-right-on-the-righ

It also reasons out why if you keep it on a stand and rotate, it will appear to be in the loosening direction, but when you actually are pedaling it while on a ride, it appears to tighten the pedal due to the above.

Thanks,

Ashok

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--

Thanks and regards,
Ashok Kumar S.

[Opendro]

Humn... I see a totally new angle of the argument now. For the benefit of others who find the Precession difficult to understand, it is like rolling a small ring inside a big ring using finger to press the small ring to the inside wall of the bigger ring. The finger and inner ring rotate in the opposite direction.

So, I see the point you are all trying to say all these while including the links - wikipedia and others. There is one big assumption there, that the pedaling force is always gravitationally downward. That is the only way how the pressure point (finger in the above ring example) can move in a cyclical motion inside the hole of the crank arm (into which pedal spindle is fit in).

Bravo! You have just found a new parameter now on how to determine if your pedaling needs improvement. If you are pedaling in perfect round, i.e. always tangential to the crank arm, the precession should never occur in the pedal spindle. It happens if you are exerting downward force all the time - both in downward as well as return motion of the stroke.

So, I agree. For majority of the cyclists, the precession will cause the spindle to tighten (assuming that the bearing balls are not too tight). It will not happen on a good cyclist. And I'm not faking when I said that a Specialized Kynkyny rider had the pedal fallen off during the criterium. It will come off if I were rider too. But I usually keep my pedal bearing a bit loose and thus it won't come off.

Bottom bracket is the opposite. If the pedaling strokes are round, it will tighten. It won't if always mashing downward.

Sorry everyone for the long exchange of the same points again and again. Thanks Prashanth, Ashok and Veloracle for the fruitful arguments and links. I would have never thought from that angle and would never have achieved the result pedaling myself.

[Ashok Kumar S]

There was this hilarious comment in that post

" -2 down vote

I once built a custom bicycle, and used a crank from another bike. I found that the crank's design differed on the donor bike, and thus, would only fit my custom bicycle when installed in the reverse direction. I saw no other problems with this solution, until one fine Spring morning, while riding my newly fabricated custom bicycle downhill at great speed, the right-hand pedal un-threaded and dropped onto the roadway. Unfortunately, my right foot followed; as did my right leg. In what seemed to be nearly a full minute of slow-motion events, my entire body followed for a meet-and-greet with the road surface on that fine Spring morning. I lay crumpled and severely injured, against a metal road sign for an unknown period of time, until a passing motorist stopped and called 911. I was transported to Emergency Central, where surgeons labored for hours to stop the bleeding and to remove my custom bicycle from its painful resting place in my rectum. Fearing the worst, a priest was summoned by the hospital staff, and my family was notified of my condition. Fortunately, I pulled through, and am able to operate my wheelchair without assistance, thanks to many months of rehabilitation and therapy. So, to answer your question; it matters little, why the pedals possess a tendency to loosen when a left-hand thread is installed on the right side. However, for the love of God; it would be in one's best interest to remember to be absolutely certain to place the pedal with right-hand threads on the right-hand side of the bicycle.

"

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[Opendro]

I got a chance to try this out today on my new commuter. Note that the pedal ball bearings are not yet tuned, i.e. n stock condition. I loosened the spindles by about 4mm. I ride about a km that has slight upslope. It comes out.

But, I have to admit, it will tighten for most cyclists as most people don't pedal round.

Tightening or precession will happen only if there is a contact force in the direction of unthreading, i.e. the finger in my example moves. In round pedaling, the contact force does not go around. If it's always say one point and tangential to the circle.

[Ali Poonawala]

Hi Open..
Your post seems to suggest your pedalling is different...or almost opposite of 'most cyclists'..since your pedalling loosened pedal further and it came out, but you say it will tighten since 'most people don't pedal round'
Do you use some clipping to pedal round' ?..anyway, how can direction be opposite ?

Curious
Ali Poonawala

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[O p e n d r o]

Direction is not opposite for me. It loosened because the pedal bearings are slightly tight as in all stock settings. I'm yet to tune it.

Most people cycle square, i.e. up and down which produce a circular contact force in the spindle thread. I'm an efficient runner too. Circular pedaling came naturally to me. That is why I'm efficient in upslope too.

[Sandeep]

On Thu, Sep 15, 2016 at 9:47 PM, O p e n d r o <ope...@gmail.com> wrote:

Most people cycle square, i.e. up and down which produce a circular contact force in the spindle thread. I'm an efficient runner too. Circular pedaling came naturally to me. That is why I'm efficient in upslope too.

Are you saying you are producing equal power in all directions with circular pedalling? 

[Opendro]

No, that is not what I meant. Most power will be between 1 O'clock and 5 O'clock with a peak at 3 O'clock, which is the same case with anybody else. The difference is the way power is transferred. That is all. If you pedal down (as if running on spot), it will create a small arc of contact force, which is why it tightens for most people. In my case, it is a single point of contact force. And this is without cleats :-) I also use runners calf to create that motion of legs displacing in opposite direction - front and back kind. Hard to explain. My team-mates who had climbed with me would know what I'm trying to say.

[Ali Poonawala]

Hi Open..
I must say I am not able to comprehend what you are saying ..

It may be that your pedalling be more efficient in terms of power delivered..
I just can not buy that the force you deliver will do reverse of what happens with less efficient pedalling of 'most people'..given that the travel of the pedal in terms of the perimeter prescribed, and the angles maintained by the foot on the pedal , remains similar, give and take a few degrees..
And when we have strong opinion running against current norms..we have a duty to convince people by substantiating it.
Otherwise it just becomes a point of  irritation,
Hope you agree with me !

Warm regards
Ali Poonawala

--

[Opendro]

Doc, I didn't update the thread for two weeks as I didn't have time to validate my claim. I validated today.

"give and take a few degrees".... that is a lot. Even for majority of the people, it is not that the contact force goes a full round around the pedal spindle thread. It is only a small arc, i.e. when you pedal down from 1 O'clock till 5 O'clock. But the direction of the arc is repeated in every stroke, which creates that force to tighten.

Of course, the precession force is way stronger than the bearing balls friction. Just that in my case, the precession does not happen. So, in the worse case, my pedal spindle will stay the same.

BTW, I have been using this bike for a month now. I could unthread the pedal easily, which also means that it didn't tighten by itself.

Sorry, I'm not going to irritate anyone further :-) Whoever wants to validate, please do so. I can show mine if anyone is interested to see a demo. I'm out second and last time from this thread.

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