Best way to remove and replace a bicycle crank arm (which tools)?

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jplee3
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Best way to remove and replace a bicycle crank arm (which tools)?

Post by jplee3 »

Hey all,

So the pedal on my kid's cheap bike (Kent Torpedo) came undone and as he was riding off pushed into the pedal and basically forced it out while it was still on the last several threads, effectively stripping the threads. We are unable to get the pedal screwed back into the crank arm now. It seems like the only option here is to replace the crank arm but I was also curious if anyone knows a quick and easy way just to get the pedal back in without all that hassle?

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If it doesn't look like there's a viable way to get it back in, what tools should I be using to remove the crank arm? There was a 16mm (? have to double check) bolt that I removed but it looks like you have to screw something else in to slowly pull the arm itself off as that thing is lodged on really tight.

TIA
bloom2708
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by bloom2708 »

Search for "bike crank puller tool" on Amazon.

https://www.amazon.com/Park-Tool-CCP-22 ... 113&sr=8-7

I have this one by Park Tools.

As you turn it in, it pushes the crank arm off.
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MP123
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by MP123 »

And note the left pedal has a reverse thread, you turn it the opposite direction to tighten/loosen. This is to keep it from unthreading while you pedal.
forgeblast
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by forgeblast »

If you cant get it back in, (and i think its reverse threaded) and you need to pull the arm off there are a bunch of different tools.
I would try wrapping it with plumbers tape the teflon stuff you might be able to get it past what is stripped to hit the threads.
https://www.modernbike.com/crank-arm-tools
fogalog
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by fogalog »

you can buy the tool or you can take it to any bike store and they will do it for you for free.

depending on which pedal it is, it is a reverse thread. from the pictures, it doesn't look bad to me. did you try putting it back in?
BIGal
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by BIGal »

Let me suggest a couple of options. If you have a bike shop you could take the pedal in and see if they recut the threads or, take both the pedal and the bike in and see if they can tap the crank arm without removing it. https://www.youtube.com/watch?v=exJtmapUR1c
Finally, you may have to purchase a new pedal if the threads are to "shot" to recut.
Vtsaxandchill
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by Vtsaxandchill »

I would consider posting and asking on reddit.com/r/bikewrench.
They will help you out and give you a link to what you need or tell you if it just needs to be taken to a shop
5280Tim
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by 5280Tim »

The bike shop might have a tap and die to clean up the threads.
SmallSaver
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by SmallSaver »

Do you like working on bikes? If so, a crank arm puller is how you get the arms off, then they just screw back on. But it's a specialized tool that's only good for that. If you're not an amateur wrench, I'd just take it to a shop. Maybe they can clean the threads, but if not the labor'll be cheap to replace.
RudyS
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by RudyS »

Lots of videos on youtube for "bicycle crank arm"
ThankYouJack
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by ThankYouJack »

With the right tool, this should be a simple and quick DIY.

It would probably take longer to drive to the bike shop, drop off the bike, drive back, and then make another round trip to pick up the bike.

Also, if you go the LBS (Local Bike Shop) route I would make sure they service e-Bikes before going there. Some by me don't, not sure why, maybe it's a liability thing.
Topic Author
jplee3
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by jplee3 »

MP123 wrote: Tue Nov 22, 2022 12:55 pm And note the left pedal has a reverse thread, you turn it the opposite direction to tighten/loosen. This is to keep it from unthreading while you pedal.
Ah thanks - maybe I'll give it another go and also try wrapping with teflon tape to see if I can get it back in...
onourway
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by onourway »

jplee3 wrote: Tue Nov 22, 2022 1:53 pm
MP123 wrote: Tue Nov 22, 2022 12:55 pm And note the left pedal has a reverse thread, you turn it the opposite direction to tighten/loosen. This is to keep it from unthreading while you pedal.
Ah thanks - maybe I'll give it another go and also try wrapping with teflon tape to see if I can get it back in...
As noted, be sure you are turning it to the left (towards the front of the bike) when tightening that pedal.

A crank puller is the tool you need to get the arm off, but then what? Unless you have a specific desire to learn how to work on bikes and don't mind the investment in decent tools, this is an easy fix at your local shop. They will probably get the pedal back in and if not, they will replace the crank arm.

If you are interested in doing it yourself, post here and I and others can help walk you through it.
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jplee3
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by jplee3 »

onourway wrote: Tue Nov 22, 2022 2:05 pm
jplee3 wrote: Tue Nov 22, 2022 1:53 pm
MP123 wrote: Tue Nov 22, 2022 12:55 pm And note the left pedal has a reverse thread, you turn it the opposite direction to tighten/loosen. This is to keep it from unthreading while you pedal.
Ah thanks - maybe I'll give it another go and also try wrapping with teflon tape to see if I can get it back in...
As noted, be sure you are turning it to the left (towards the front of the bike) when tightening that pedal.

A crank puller is the tool you need to get the arm off, but then what? Unless you have a specific desire to learn how to work on bikes and don't mind the investment in decent tools, this is an easy fix at your local shop. They will probably get the pedal back in and if not, they will replace the crank arm.

If you are interested in doing it yourself, post here and I and others can help walk you through it.


So I tried getting replacement parts under the manufacturer's warranty but they are telling me I cross-threaded the pedal when installing and they won't replace under warranty. I don't recall which direction I installed the pedal but I don't specifically recall having a hard time installing the pedal (so I think I did install it correctly and it just came loose?)... when I was trying to get the pedal back on though, I did make the mistake of trying to thread it on the wrong way (doh) so that might have caused what is seen in the pics (as the pics were taken after that).

I do have an extended warranty from where I bought it so I'm wondering, if I can't get the replacement parts through the manufacturer, if I should just open a claim through extended warranty... the only concern is if the extended warranty will take into consideration if I tried filing a claim with the manufacturer and deny me again based on the fact that the manufacturer denied me.

Ugh, such a pain....
plats
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by plats »

I doubt you damaged the threads by screwing it in the wrong way. It won't go in at all clockwise. Anyway, I just Googled and found you can buy a left side crank arm separately and should be able to get one for under $15.
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jplee3
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by jplee3 »

plats wrote: Wed Nov 23, 2022 1:30 pm I doubt you damaged the threads by screwing it in the wrong way. It won't go in at all clockwise. Anyway, I just Googled and found you can buy a left side crank arm separately and should be able to get one for under $15.
After the thing got stripped I was able to get it to go clockwise for a little but didn't want to keep going so I stopped after I could get it just tight. But that was probably after it had been stripped regardless...

Do you have a specific link? Are these crank arms model specific or are they 'generic' in that I can get any left side crank arm (of the same length) and it'll work fine? Or am I going to want to buy a couple crank arms for each side? I'm also not sure if the pedal is going to fit on there as is in the case that the pedal bolt threads are stripped too.
plats
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by plats »

I Googled "left side mountain bike crank arm" and found many. You'll have to get one the same length, square hole and probably pedals, too. Too bad you're not near me because my friends and I have boxes of unneeded bike parts.
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jplee3
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by jplee3 »

plats wrote: Wed Nov 23, 2022 2:12 pm I Googled "left side mountain bike crank arm" and found many. You'll have to get one the same length, square hole and probably pedals, too. Too bad you're not near me because my friends and I have boxes of unneeded bike parts.
At this point, maybe I'll just buy new pedals and at least the left side crank arm. Or if they sell a set of both crank arms and pedals that might be easier...
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MP123
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by MP123 »

jplee3 wrote: Wed Nov 23, 2022 2:02 pm Do you have a specific link? Are these crank arms model specific or are they 'generic' in that I can get any left side crank arm (of the same length) and it'll work fine? Or am I going to want to buy a couple crank arms for each side? I'm also not sure if the pedal is going to fit on there as is in the case that the pedal bolt threads are stripped too.
It may be hard to get an exact match for just the left crank arm. The length and "q-factor" are important, it appears to be a square taper bottom bracket. But you want the arm to look the same (i.e. same brand) as the right side too or it will just look goofy.

The right side arm may be part of the crank so you might need to get a new crankset and pedals if you go that route. Or just take it to your local bike shop and see if they can just chase the threads and clean them up enough to get it back together.
campy2010
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by campy2010 »

jplee3 wrote: Tue Nov 22, 2022 1:53 pm
MP123 wrote: Tue Nov 22, 2022 12:55 pm And note the left pedal has a reverse thread, you turn it the opposite direction to tighten/loosen. This is to keep it from unthreading while you pedal.
Ah thanks - maybe I'll give it another go and also try wrapping with teflon tape to see if I can get it back in...
Please don’t do this. It’s the most dangerous solution.
IowaFarmBoy
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by IowaFarmBoy »

You might look into putting a helicoil insert into the crankarm to repair the damaged threads. The pedal will thread into the helicoil. Something like this below (you'll need to determine the correct size threads and get the correct direction on the threads since they are different between the left and right side- this listing is just an example.) Your local bike shop might be experienced in doing this.

https://www.amazon.com/BILITOOLS-M6x1-0 ... hdGY&psc=1
Tracker968
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by Tracker968 »

You need to clean up the threads with a thread die. But a die would cost more than a new pedal. If you are patient and careful you could use a small file to clean up the threads. Then thread it in counterclockwise. Don't use Teflon tape and make sure it is very tight.

If you don't have the tools or aren't really interested in spending an hour working on it, then I would just take it to a bike shop.
plats
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by plats »

Just checked your photo and it is not a square hole, it's diamond.
wunder
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by wunder »

If you did in fact strip the threads on the pedal, crankarm, or both you are going to want a new pedal and crank arm. The arm is definitely square taper. But as noted those come in different lengths, finishes, and sometimes different expected bottom bracket spindle lengths (103-123mm for example). If in doubt I strongly suggest going to a bike shop and paying for help. Pedals failing on the road is not fun or safe.

As others have noted the right tool is called a "crank puller" which threads into the crank by the BB and pushes down on the spindle to extract the crank arm. Pedals are reverse threaded on the non drive side (tighten towards the front of the bike) so that they don't come off.
onourway
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by onourway »

jplee3 wrote: Wed Nov 23, 2022 2:22 pm
plats wrote: Wed Nov 23, 2022 2:12 pm I Googled "left side mountain bike crank arm" and found many. You'll have to get one the same length, square hole and probably pedals, too. Too bad you're not near me because my friends and I have boxes of unneeded bike parts.
At this point, maybe I'll just buy new pedals and at least the left side crank arm. Or if they sell a set of both crank arms and pedals that might be easier...
Unlikely you need new pedals. However you will need a crank puller and understand how to use it properly, or you will end up with another set of stripped threads and a crank arm stuck on the bottom bracket.

At this point based on what I'm hearing from you, your best bet is to really take it to a shop. They will be able to identify whether the arm and pedal can be repaired (via a tap, helicoil, etc.) or must be replaced. That part will not be very expensive; I would expect $50-70 or so - not much more than you will spend on parts and tools yourself. Given that this appears to be a bike that you assembled, I would highly recommend having them do a tune up on it as well. They will check the gears, brakes, wheels, headset, everything to make sure it is assembled properly, tight, working at its best, and won't come apart again.
StrongMBS
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by StrongMBS »

From your pictures it is hard to tell how bad the treads on the pedal and crank are stripped and for how many turns. If the threads are not damaged to badly, they can be cleanup even without the proper tools (tap and die). Pictures of the threads from a couple of sides would help.

Since they are exposed the treads on the pedal are easier to clean up with a small file if they are not to damaged too badly. The threads in the crank are harder to get to and cleanup without a tap. The key is to remove all the cross-threads.
If you can get rid of the cross-threads, you might be able to carefully get the pedal to seat properly (using a little grease will help). Depending on the material the pedal and crank are made of one trick if you can get the pedal threads clean up enough is to thread the pedal into the back of the crank, remember they are reverse threads. This will use the crank threads as a die on the pedal threads. If you are lucky and the pedal threads are long enough, they will then act as a tap on the crank threads once they are screwed all the way in. If you look at the back of the other crank, you will be able to see how long the pedal threads are to the crank thread.

But your best bet is if you have a local bike shop with a kind owner who can do this with a tap and die in 5 minutes for free or minimum cost.
Atilla
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by Atilla »

I'd be tempted to get some JB Weld, slather it all over the bad threads and screw/pound it back in tight.

Let it dry for a day or two and see if it holds.

Kid's gonna grow out of the bike soon enough anyway.

I have an MS in Shadetree Mechanic. :beer
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by Sandtrap »

Options:
1. "J.B.Weld" as suggested. Worth a try.
or
2. Bike shop. Leave it to the pros. They may have pedals too.
or
3. Do you have a mig welder and welding skills?

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dratkinson
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Re: Best way to remove and replace a bicycle crank arm (which tools)?

Post by dratkinson »

(1) I notice on my bike, that the pedal can be screwed into the crank arm... from the back side. So, if your pedal bolt goes all the way through the crank arm, if you screw it into the crank from the back side, it might straighten the messed up internal threads on the crank's front-side enough to allow you to start the pedal from the front.*

* First use a triangular file on the pedal's external threads to ensure they are straight, before trying to screw it into the backside of the crank.


(2) If the pedal bolt does not go all the way through the crank arm, then screwing it in from the back-side, it'll never reach the messed up internal thread on the crank's front-side. So, never mind. (I notice that my pedal bolts do not go all the way through my crank arm, so I could not fix your problem this way, if it were on my bike.)

In which case I'd take it to a LBS and pay them to fix it; it shouldn't be that much.* (Call several and ask "How much to repair?")

* You could try to buy a thread repair kit (taps, thread inserts,...), but it'd probably cost more (time, money) than paying the LBS.

See "Crank Saver Kit, $225": https://uniorusa.com/products/crank-saver


(3) Or it might be cheaper to buy a new/old crank from your LBS.

Recall my LBS has been in business for many years, and has many spare parts---in drawers from disassembled old bikes---that they sell to budget-conscious folks. So the part is almost free, and I just pay LBS labor to install it---a reasonable fraction of the hourly rate. It keeps me coming back.

So you may have the option to buy a new/old part* and install it yourself**, or pay the LBS to do it for you.

* The LBS would need to see your old crank/pedal, to ensure they have an old part of the size (color, less important).


** (4) Recall from reading about bike maintenance, it's recommended that we periodically maintain (clean, lubricate, adjust, tighten,...) our bikes to keep them in good working order. So this could be an opportunity for junior to learn*** and get into the habit of checking/maintaining his bike. Perhaps you/he could spend part of a Saturday morning learning/doing this.

So if you buy a new/old part from your LBS, you/he could get started by letting him install the part. (Dad just adds the extra "umph" to ensure the bolts are tight on the replaced part. Or could teach him how to use a "cheater pipe"---a piece of pipe slipped over a socket wrench to increase torque---to tighten the bolts for himself; tie other crank arm to seat down tube to secure crank for bolt tightening.)

After which, you/he could clean, lubricate, adjust his bike. (Brakes re-centering is often needed to avoid rubbing on wheel.)

*** Could teach junior how to research "bike maintenance" topics for himself. Perhaps this will be the impetus which creates a new ME (mechanical engineer). :happy



(Added) (5) Oops! Forgot that it might be possible to DIY tools to restore damaged internal (tool: tap) and external (tool: die) threads.
See: https://www.youtube.com/watch?v=HvoJ3awG7HM

Video shows using a larger drill bit to make tap/die. A slightly smaller drill bit should work too. A larger bit removes more material to create tap/die, which gives more space for chips to fall out; but removing more material could make a weaker die. (I've never done this so don't have a good feel for how much material is too much to remove.)

From the video, it looks like the strongest dies would be created by aligning the nuts' points/flats, and then drilling the holes at the nuts' points---avoid drilling holes in the thinner material at the nuts' flats.

The DIY tap/die should be made from material that is a little harder than the material into which you want it to cut/repair threads.

Right-hand threaded bolts/nuts---from which to make right-hand tap/die---are common/cheap, just buy from hardware store.

Left-hand threaded bolts/nuts---from which to make left-hand tap/die---are more rare/expensive, so it might be cheaper to let LBS do the repair.
See left-hand bolts: https://www.mcmaster.com/bolts/thread-d ... left-hand/
See left-hand nuts: https://www.mcmaster.com/left-hand-threaded-nuts/
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