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Pedals to Crank arm sizing

Old 05-11-22, 08:34 AM
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damnbike
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Pedals to Crank arm sizing

Are there different thread pitches and shaft sizes to pedals and crank arms, or is it universal? I'm winding up with crossed/stripped threads. When I search on google for crank arms and pedals, they always come separate. My pedal fell off, the threads were all stripped inside the crank arm. I put a new crank arm on with the same pedal, and I coiuldn't get the pedal on the crank arm without crossing the threads. How do I stop this from happening?
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Old 05-11-22, 08:41 AM
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PS, I may have mixed up the left/right crank arms. What's the difference between the left and right crank arms?
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Old 05-11-22, 08:48 AM
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Right crank/pedal is normally right threaded. Left crank/pedal is normally left threaded.

Most common today are 9/16" x 20 tpi. On old one piece cranks and some other bikes 1/2" x 20 tpi is found. At various times, mostly with vintage bikes pre 1970, you'll find some different thread types and directions.

If you mixed up the crank arms, it makes me think you may have one of those very old bikes that might have different threading's and directions. And maybe won't be compatible with any new pedals.

Put a pic in the gallery here and someone might try to find it. Though you only need 1 more post and maybe a full day to be able to post pics.

Last edited by Iride01; 05-11-22 at 08:56 AM.
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Old 05-11-22, 09:02 AM
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Originally Posted by damnbike View Post
PS, I may have mixed up the left/right crank arms. What's the difference between the left and right crank arms?
Left and right threads. Hopefully you didn't damage the threads in your crank arms by forcing the pedals into the wrong threads.
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Old 05-11-22, 09:03 AM
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Originally Posted by damnbike View Post
PS, I may have mixed up the left/right crank arms. What's the difference between the left and right crank arms?
The right one has the chainwheels attached?

Also--often the pedals themselves, usually on the axle, will be marked with "L" and "R."
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Old 05-11-22, 09:06 AM
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I've never tried, so I don't know...but could you even start left hand threads into a right hand crank, or vice-versa?
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Old 05-11-22, 10:30 AM
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Originally Posted by cxwrench View Post
Left and right threads. Hopefully you didn't damage the threads in your crank arms by forcing the pedals into the wrong threads.
I did strip the threads on the crank arm, then put on a spare crank arm, and crossed the threads on that too
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Old 05-11-22, 10:31 AM
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Originally Posted by smd4 View Post
The right one has the chainwheels attached?

Also--often the pedals themselves, usually on the axle, will be marked with "L" and "R."
Well, this was on the chainwheel side, I replaced it with a spare, but I didn't know if the spare was left or right.

I might have mixed up the pedals too I didn't know everything was different left and right.
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Old 05-11-22, 10:34 AM
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Originally Posted by damnbike View Post
I might have mixed up the pedals too I didn't know everything was different left and right.
Look for the "L" and "R" stampings on the pedal axles, near (or on?) the wrench flats. The threads are different on the left so the pedal doesn't unscrew itself while you're pedaling.
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Old 05-11-22, 10:43 AM
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Originally Posted by smd4 View Post
I've never tried, so I don't know...but could you even start left hand threads into a right hand crank, or vice-versa?
it has been done more often than you would think, hard steel, softer aluminum, no finesse (ready gorilla like force)
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Old 05-11-22, 10:48 AM
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If the threads aren't buggered up too bad, you might can run something through from the other side and straighten the threads enough to install the pedals properly. A pedal might do that if the treads are long enough to go all the way. If not you'll have a hard time finding something long enough that is left threaded.

However if you did not notice that things where right and left threaded or that you were cross-threading, then maybe you should go to a bike mechanic with this.

DIY is better learned when everything is correct. Otherwise, you'll probably get some misconceptions right from the start that will be hard to rid yourself of.

And still, we are a little confused about you saying you can swap left and right cranks. Are there any part numbers or brand and model stamped on the cranks? Again, how about putting a pic in the gallery and we'll look for it if you can't now directly post them in your replies here.
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Old 05-11-22, 10:55 AM
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Originally Posted by damnbike View Post
Well, this was on the chainwheel side, I replaced it with a spare, but I didn't know if the spare was left or right.
I *think* you're saying you replaced the pedal you tried to install with a "spare?"

Is this the same bike that you're having trouble with the chain?
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Old 05-11-22, 02:05 PM
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Originally Posted by damnbike View Post
I did strip the threads on the crank arm, then put on a spare crank arm, and crossed the threads on that too
So the first time wasn't the learning experience it should've been.

Originally Posted by smd4 View Post
Look for the "L" and "R" stampings on the pedal axles, near (or on?) the wrench flats. The threads are different on the left so the pedal doesn't unscrew itself while you're pedaling.
Some pedals have L and R but many don't. If they don't then there will ALWAYS be something to tell left from right if you can't tell by looking at the threads. A groove around the axle right next to where it threads into the crank arm or grooves perpendicular to the axle in the spot. There is ALWAYS a telltale.

Originally Posted by Iride01 View Post
If the threads aren't buggered up too bad, you might can run something through from the other side and straighten the threads enough to install the pedals properly. A pedal might do that if the treads are long enough to go all the way. If not you'll have a hard time finding something long enough that is left threaded.

However if you did not notice that things where right and left threaded or that you were cross-threading, then maybe you should go to a bike mechanic with this.

DIY is better learned when everything is correct. Otherwise, you'll probably get some misconceptions right from the start that will be hard to rid yourself of.

And still, we are a little confused about you saying you can swap left and right cranks. Are there any part numbers or brand and model stamped on the cranks? Again, how about putting a pic in the gallery and we'll look for it if you can't now directly post them in your replies here.
You mean 'something' like a tap that's sole purpose is to clean up threads?
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Old 05-11-22, 02:31 PM
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Originally Posted by cxwrench View Post
You mean 'something' like a tap that's sole purpose is to clean up threads?
No, not in light of all the other mis-steps the OP has already done. Taps, even those made just to clean up threads are more easily started wrong and can make a bigger mess of things when in the hands of someone not able to tell when they are doing it wrong. And if bought by mistake, taps for cutting new threads might just break and get jammed in the hole if the OP isn't familiar with using them properly.

But I guess if the OP needs to pay the tuition to DIY school, this is as good as any to incur those fees.
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Old 05-11-22, 04:34 PM
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If you manage to get old French pedals or cranks from the 60's or 70's, they're very close to the standard 9/16 pedals, and will cause all sorts of headaches.

As mentioned above, remember for pedals it is right side, right thread, left side, left thread.

For bottom brackets it is just the opposite, right side, left thread, and left side, right thread (with a few more specialty variations than the pedals).

I presume one of the reasons the threads get bungled is that people overtighten the left side trying to remove the pedals.

Always hand tighten screws until you get several turns before grabbing for the wrenches. Sometimes turning backwards a couple of turns will help you orient the shaft before threading it in.

If pedals have stripped the threads, then make sure the threads are super-clean before reusing.

A good shop may be able to helicoil stripped crank threads, but for a cheap bike, doing so may be more expensive than just replacing the crank. Nonetheless, a good helicoil job should be permanent, and might be better than new.
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Old 05-12-22, 11:19 AM
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Originally Posted by smd4 View Post
Look for the "L" and "R" stampings on the pedal axles.
If you have an old Peugeot or Gitane with Lyotard pedals, it could be stamped "D" and "G."

So, to answer your question ...

Originally Posted by damnbike View Post
Are there different thread pitches to pedals and crank arms?
​​​​​​​
Yes.
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Old 05-12-22, 11:29 AM
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Originally Posted by damnbike View Post
Are there different thread pitches and shaft sizes to pedals and crank arms, or is it universal? I'm winding up with crossed/stripped threads. When I search on google for crank arms and pedals, they always come separate. My pedal fell off, the threads were all stripped inside the crank arm. I put a new crank arm on with the same pedal, and I coiuldn't get the pedal on the crank arm without crossing the threads. How do I stop this from happening?
Tell us all you can about the bike (manufacturer, model, year), the cranks and the pedals. Pictures will be a help. As said above, there is more than one pedal thread standard. Most bikes now stick to the common standard but older French and (I believe) US bikes had different standards.
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Old 05-12-22, 11:43 AM
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based on pic in the other thread the bike is lower end diamondback, with square taper bottom bracket. It is would be amazing if it was anything other than standard 9/16 size pedals.

OP needs to
  1. replace cranks or
  2. get helicoil job done
  3. find a bike mechanics class to to take or watch in detail how to videos before touching another thing on the bike
  4. find a way to work with bike not upside down, can just hang from a pair of ropes. this will make all things easier
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Old 05-12-22, 01:33 PM
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It's likely that the threads on the pedal spindle are filled with leftover aluminum from the first damaged crank and this is preventing the threads from properly engaging with the crank threads. Use a file or needlenose pliers or the like to get all that crap out of the threads before you try to thread it in again.
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Old 05-12-22, 02:03 PM
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Old 05-12-22, 02:11 PM
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Originally Posted by squirtdad View Post
4. find a way to work with bike not upside down, can just hang from a pair of ropes. this will make all things easier
My go-to strategy when I don't have a proper bike stand is to hook the nose of the saddle over a tree branch or rafter or whatever overhead item I have handy. As long as the front wheel is on, the bike will be balanced with the front down and this will keep it from falling. You can also wrap some rope or other tying material around the seatpost and whatever the saddle is hanging on to further stabilize it.
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Old 05-12-22, 08:39 PM
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Originally Posted by SurferRosa View Post
If you have an old Peugeot or Gitane with Lyotard pedals, it could be stamped "D" and "G."

So, to answer your question ...



Yes.
Back in the days of the TdG and the early years of ToC, and a lot of the other big races there would be a 'talker' in the Commissaire's car that told everyone in the team cars what was coming up over Radio Tour. Hour after hour of 'Virage a Droit' or 'Virage a Gauche'.
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Old 05-13-22, 12:18 AM
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Originally Posted by SurferRosa View Post
If you have an old Peugeot or Gitane with Lyotard pedals, it could be stamped "D" and "G."

So, to answer your question ...


​​​​​​​
Yes.
If the pedals are Italian, you may get "D" for Destra and "S" for Sinistra. However, I believe they all have the 9/16 x 20tpi, even though other parts had bizarre thread combinations.
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Old 05-13-22, 09:02 AM
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His bike's a Diamondback. I'd bet 5 dollars he doesn't have Italian or French pedals.
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Old 05-13-22, 10:56 AM
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Originally Posted by smd4 View Post
His bike's a Diamondback. I'd bet 5 dollars he doesn't have Italian or French pedals.
Give me odds, and you're on!!
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