# Crank Arm Threads Stripped



## coopdad (Nov 6, 2010)

Guys, I was out riding tonight and I noticed that the pedal felt a little different. When I looked down the pedal was halfway out and slightly cocked sideways. When I took it off, at least half the threads were stripped out. 

My questions is can I take the arm to someone that can weld aluminum and have them add metal that can be tapped again?

In case it matters: the cranks are Truvativ Isoflow and of course it is the chain ring side. The back of the arm says IF4KFD 175

Thanks for the advice,
John


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## rideonjon (May 27, 2009)

heli-coil it


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## rockcrusher (Aug 28, 2003)

They can usually help you heli coil it at an ACE or Tru-Value hardware store and if not they usually sell a helicoil kit. It is a small spring that screws into the arm to replace the damaged threads after you tap it our one size larger. It works really well and is permanent. 

Just remember to check the tightness of your pedals in the future, and for that matter most of the bolts on your bike.


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## J Ro (Jan 13, 2004)

You have to make sure you get it in straight, which may be hard your first time. You may want to take it to a machine shop to have the job done properly.


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## coopdad (Nov 6, 2010)

Thanks guys. I will see if Home Depot or Lowes has them (they are both right down the street... no Ace around here that I can think of). There is a Pep Boys right beside Home Depot too.

I suppose I just need to bring a pedal to double check the size.



rockcrusher said:


> They can usually help you heli coil it at an ACE or Tru-Value hardware store and if not they usually sell a helicoil kit. It is a small spring that screws into the arm to replace the damaged threads after you tap it our one size larger. It works really well and is permanent.
> 
> Just remember to check the tightness of your pedals in the future, and for that matter most of the bolts on your bike.


Crud, yes, will double check the tightness of the petals on my other bikes too. I have been pretty paranoid about not being able to get pedals off after unsuccessfully trying to remove one off another bike lately. I immediately went out and cracked every petal loose...am guessing I did not get this one back on well enough the last time I worked on it.


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## RTM (Sep 17, 2005)

coopdad said:


> Thanks guys. I will see if Home Depot or Lowes has them (they are both right down the street... no Ace around here that I can think of). There is a Pep Boys right beside Home Depot too.
> 
> I suppose I just need to bring a pedal to double check the size.
> 
> Crud, yes, will double check the tightness of the petals on my other bikes too. I have been pretty paranoid about not being able to get pedals off after unsuccessfully trying to remove one off another bike lately. I immediately went out and cracked every petal loose...am guessing I did not get this one back on well enough the last time I worked on it.


I suggest a good bike repair manual. The park big blue book is awesome. Reason being, it has suggested torque values for most common bolts. And proper technique for removing/replacing parts. It's really an invaluable "tool" for anyone who works on their bike. I really learned a lot.

Regarding the crank arm, I suggest you just buy a replacement set of cranks. You can find a lower end, used set for about as much as you'll pay to repair this one. I'm never a fan of patch jobs. Just one more thing to fail in the future.


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## DiRt DeViL (Dec 24, 2003)

Agree, replace the crank or entire set. The problem may come back the next time you try to remove the cranks, it has happened to me and have ended up getting new ones.


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## stukov (Mar 26, 2011)

Pedal was badly inserted in the first time! 
You can get it welded and recut the thread of course, it's cheap, it must be.
I wouldn't throw away the crankset...


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## stukov (Mar 26, 2011)

Similar problem, the thread of the derailleur hanger gone wrong on my bike, the repair cost me 10$.
( I live in Hungary)


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## coopdad (Nov 6, 2010)

Let's say I do as you suggest and use this "opportunity" to upgrade my stuff. What do I need to know when looking at other brands will fit the existing BB? 
Money is super-tight right now so upgrading might not be possible, plus it is not a high end bike so I shouldn't put a lot of money into it. But it is certainly worth the time it takes to do a Google search.


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## Berkley (May 21, 2007)

Any bike shop worth their salt should be able to helicoil it, but the cost of a single replacement arm may be very close.


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## SgtBaxter (Jul 2, 2011)

If you're thinking upgrade, you need to know what bottom bracket you have, which you can probably look up on bikepedia. Or just take the crank arm off if you have a puller.

If it's an inexpensive bike as you say its probably a good old regular square taper.

Edit... I Googled the Isoflows, they fit square taper brackets. Also, a new crankarm looks to be about $13. To hell with repair at that price.

Sent from my DROIDX using Tapatalk


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## coopdad (Nov 6, 2010)

Thanks Sgt. I will give it a look.

Another (quick) question: I cannot seem to get the silver allen bolt out. If is "lefty Lucy"?


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## AndrwSwitch (Nov 8, 2007)

Yeah, but it's in there pretty tight. Torque specs for these things can be very high, depending on the type of bottom bracket.


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## David C (May 25, 2011)

I think you should get another crankset, as I personally would never rely on a pre-damaged repaired crank arm to withstand my whole body weight and torque. And I'm not even on the heavy side at all. You can get a FSA A-Drive or Shimano Alivio crankset, 22-32-44 for around $30 and it will be better then what you actually have. You gotta know that aluminum is not steel. And if aluminum fail once, it will fail again. That's why most crank arms have steel inserts for the pedal's threads.

I had one pedal coming loose last year, so I've took a look and the whole arm's thread was striped inside. I'll tell you 5 mins later that arm was in the recycle bin. It's not something you want to take chances with.

David

Edit : you could also get a new crank arm only, but I doubt you could find one, as entry level cranks don't really get that much spare parts... But if you find a used 175mm crank arm that has the right spacing for your rings, you could simply replace the arm and swap the rings into the new arm. You'll need a 4 arm spider, square taper, 175mm and with the right BCD (bolt center diameter) size for the rings. Look around eBay 

David


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## coopdad (Nov 6, 2010)

This is great info. Now I actually have options that do not break the bank... Thanks!
One last question. Some of the cranksets on Ebay state "9 speed compatible"... compatible meaning "will also work with.". I assume my 8 speed will work with it.


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## jaynestown (Oct 23, 2011)

9 speed chain is a little more narrow. I don't think you'd have any trouble running an 8speed chain on the crank, but maybe someone else can chime in to be sure. 

And I agree with David C...definitely better to just get a new crankset.


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## EclipseRoadie (Oct 7, 2007)

Isoflow's are pretty cheap, and I've got one of them in my garage with one side with (surprise, surprise) stripped pedal threads... which arm is it, I'll give you my good one for free if you want it
. PM me if you want, and we'll figure out if we've got two good crank arms between us.


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## David C (May 25, 2011)

double post


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## David C (May 25, 2011)

jaynestown said:


> 9 speed chain is a little more narrow. I don't think you'd have any trouble running an 8speed chain on the crank, but maybe someone else can chime in to be sure.
> 
> And I agree with David C...definitely better to just get a new crankset.


Any 9 speed crankset will work with a 8 speed chain.

Just be careful not to get a 10 speed crankset, as the chainring spacing is much more narrow and won't allow your 8 speed chain to properly fit on the crank.

And what I usually do when removing a crank bolt that is very tight, I insert the hex key in a way that I can clamp my hand over the crank arm and the hex key to press them together, allowing better and more directional torque to be applied. Just be careful not to snap your hand when it get loose... It kinda hurt.

David


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## coopdad (Nov 6, 2010)

Another question that has come up:
Crank arms that fit come in either 170 or 175. If I am thinking totally new, what are the advantages/disadvantages to each size?

And square tapers... I seem to remember seeing that Shimano's square taper is a different size than the others' square taper. Anyone know this?


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## SgtBaxter (Jul 2, 2011)

In reality for the average joe there isn't much difference between a 170 and 175. 

The 175 will let you make power a little more instantly, the 170's will be better for spinning.

The Shimano cranks should fit your bottom bracket. How old is the bike? Might consider a new BB anyway, the UN-54 is only $15-$20 depending on the size you need.


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## coopdad (Nov 6, 2010)

SgtBaxter said:


> In reality for the average joe there isn't much difference between a 170 and 175.
> 
> The 175 will let you make power a little more instantly, the 170's will be better for spinning.
> 
> The Shimano cranks should fit your bottom bracket. How old is the bike? Might consider a new BB anyway, the UN-54 is only $15-$20 depending on the size you need.


Good info. I have bad knees so I have to limit how much pressure I put on them... need to do more spinning than powering, even if it a tiny amount more.

The bike is a 2005 Fuji Nevada. I think it was typical of beginner Mountain Bikes around here... purchased because "they are cool" and only ridden a few times. Nothing on it was worn so I am guessing BB is good to as the only real miles on it were put on by me in the past year.

I did do a search for the BB you mentioned and Jenson says it fits "shimano, sugino, truvativ, and most other cranks".
Thanks again guys!


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