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Old 09-25-11, 06:17 AM   #1
roysclockgun
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Classic Error : Stripped Left Hand Threads

I have had the Giant Boulder for eight years. The hard plastic, covering the pedals was splitting. I picked up a new set of pedals and began to take off the old. The fact that the left pedal used left hand threads completely went out of my 70 year old mind. Commonly called a "senior moment". Using a force arm on the wrench, I turned the bolt on the pedal the wrong way, thus stripping the treads in the alumium crank arm. I am going to get the pedal unscrewed and try to epoxy the new pedal in place, as the damage is already done. Or : Suggestions?
Best,
Steven in DeLand
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Old 09-25-11, 07:33 AM   #2
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Steven: The crank arm can be drilled out and tapped for a threaded insert called a Helicoil, which will restore your threads. Check with your local bike shops or less likely, a machine shop. You will need to end up with a 9/16x20 left-hand thread. You could also buy a replacement left crank arm. I wouldn't recommend epoxying the new pedal into the stripped crank.

Whatever approach you take, be sure to grease the threads of the new pedals before you mount them to prevent seizing of the dissimilar metals. I recommend Tef-Gel. Stainless steel pedal washers may also help get them loose when the time comes.

Use a proper pedal wrench when you mount the new pedals and torque them well, loose pedals are the leading cause of stripped crank threads. It sounds as if you were able to exert plenty of force with the tool you used, though.

Last edited by dsbrantjr; 09-25-11 at 07:37 AM. Reason: add pedal torque comment
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Old 09-25-11, 09:25 AM   #3
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Steven: The crank arm can be drilled out and tapped for a threaded insert called a Helicoil, which will restore your threads. Check with your local bike shops or less likely, a machine shop. You will need to end up with a 9/16x20 left-hand thread. You could also buy a replacement left crank arm. I wouldn't recommend epoxying the new pedal into the stripped crank.

Whatever approach you take, be sure to grease the threads of the new pedals before you mount them to prevent seizing of the dissimilar metals. I recommend Tef-Gel. Stainless steel pedal washers may also help get them loose when the time comes.

Use a proper pedal wrench when you mount the new pedals and torque them well, loose pedals are the leading cause of stripped crank threads. It sounds as if you were able to exert plenty of force with the tool you used, though.
+1. I'd highly advise against epoxying the pedal into the arm. You might want to check and see if your LBS has an extra crank arm to sell from the spare parts bin. Bonus if you don't mind if it looks different. The only salient specifications are crank length arm, and bottom bracket style.
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Old 09-25-11, 09:36 AM   #4
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Buy a new (or used) crank arm and be done with it.
Epoxy is not something I would use where my life is at stake.
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Old 09-25-11, 09:38 AM   #5
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Originally Posted by roysclockgun View Post
I have had the Giant Boulder for eight years. The hard plastic, covering the pedals was splitting. I picked up a new set of pedals and began to take off the old. The fact that the left pedal used left hand threads completely went out of my 70 year old mind. Commonly called a "senior moment". Using a force arm on the wrench, I turned the bolt on the pedal the wrong way, thus stripping the treads in the alumium crank arm. I am going to get the pedal unscrewed and try to epoxy the new pedal in place, as the damage is already done. Or : Suggestions?
Best,
Steven in DeLand

Did you get the pedal all the way on cross-threaded, or only a few threads? If the latter, simply get hold of a left-handed pedal tap or pay your LBS to run the tap through starting from the good threads on the inside.

Don in Austin
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Old 09-25-11, 09:43 AM   #6
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Did you get the pedal all the way on cross-threaded, or only a few threads? If the latter, simply get hold of a left-handed pedal tap or pay your LBS to run the tap through starting from the good threads on the inside.

Don in Austin
I think the pedal was already on, and he kept tightening it (instead of loosening) with such force that the threads stripped out. Thus, I would assume there's not much left in there.
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Old 09-25-11, 09:54 AM   #7
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It can be retapped, no problem.

Here is the process. If you don't feel up to taking it on, call around for a shop that offers this service. The repair taps are quite expensive.
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Old 09-25-11, 12:24 PM   #8
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It takes a staggering amount of torque to strip a 9/16" thread by overtightening. I'm curious to know how long a cheater bar the OP used, and if it was less than 2 feet, I'd like to see a photo of his biceps.
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Old 09-26-11, 04:36 AM   #9
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Thanks for all the tips.
In order to screw this job up, I had removed the crank arm from the bike and wrapped it with leather, than snugged it into my bench vise. A 19/32" open end wrench fit the flats on the pedal very well. Since I could not strip the aluminum thread with just the force that I could exert using the 8 1/4" long wrench, I got the steel tube used to lock down the leveler bars on my travel trailer. The tube is 18" long, with a 7/8", inside diameter. That gave me a 26" long force arm, when I slipped the tube over the jaw of the wrench and hung on it. The first turn was difficult, than as I now know, when the aluminum threads failed, the job got easier. By time I realized my error the threads were toast and were not coming out of the crank arm at all.
I phoned the local bike shop and they are working on finding me a crank arm, or getting the a bushing to fit into the reamed out hole.
Thanks again guys,
Steven
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Old 09-26-11, 05:32 AM   #10
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All I can say is that I hope when I am 70, I'll still be riding and maintaining my bike(s), and strong enough to strip a crankarm by over-tightening a pedal. My hat's off to you, sir! Color me impressed.
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Old 09-26-11, 06:08 AM   #11
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Roy, that method works but probably is faster just go and buy a new crank or crankset as somebody mentioned before. Depends of the way u want to go, besides cranks aren't that expensive if u get a used one, maybe even free.
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Old 09-27-11, 06:25 AM   #12
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Yeah, I hear ya. Going to phone the shops as soon as they open up. I went to two shops in DeLand, FL., yesterday. Both were closed up. Gone! Sad commentary on the world economy today!
Tastewar : Thanks for the kind words! My only answer is to say first, all credit goes to God for giving me a body that, if I try, can keep going. Secondly, as a steward of this body, I must keep up exercise. I bicycle 10 to 20 miles a day. Granted, I am in FL. with no hills to speak of. I lived most of my life in Maryland, where I bought the Giant, Boulder bike. The trails around the reservoir were brutal and today, I could not do it. I tell anyone who ask, that the secret to keeping fit is to "give" to yourself at least one hour per day and keep up that one hour or more exercise. And I mean sweat creating exercise. My dentist said that she does not have time to do that. She is in her late 40s. So, I ask her how much time she spends generating cash in her practice and she said 40 hrs./week. I then ask her if she could get up one hour earlier, or go to bed one hour later, because after spending 40 hrs./week generating cash, she really needs to give her body at least 7 hr./week, doing exercises, in order to keep the body going! That is the way one must look at it.
In my 70th year, I am no where near ready to sit in front of the TV and wait for the grim reaper! God willing, I will keep on biking for another 20 years.
Best,
Steven
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Old 09-27-11, 08:31 AM   #13
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Yeah, I hear ya. Going to phone the shops as soon as they open up. I went to two shops in DeLand, FL., yesterday. Both were closed up. Gone! Sad commentary on the world economy today!
Tastewar : Thanks for the kind words! My only answer is to say first, all credit goes to God for giving me a body that, if I try, can keep going. Secondly, as a steward of this body, I must keep up exercise. I bicycle 10 to 20 miles a day. Granted, I am in FL. with no hills to speak of. I lived most of my life in Maryland, where I bought the Giant, Boulder bike. The trails around the reservoir were brutal and today, I could not do it. I tell anyone who ask, that the secret to keeping fit is to "give" to yourself at least one hour per day and keep up that one hour or more exercise. And I mean sweat creating exercise. My dentist said that she does not have time to do that. She is in her late 40s. So, I ask her how much time she spends generating cash in her practice and she said 40 hrs./week. I then ask her if she could get up one hour earlier, or go to bed one hour later, because after spending 40 hrs./week generating cash, she really needs to give her body at least 7 hr./week, doing exercises, in order to keep the body going! That is the way one must look at it.
In my 70th year, I am no where near ready to sit in front of the TV and wait for the grim reaper! God willing, I will keep on biking for another 20 years.
Best,
Steven


You can find left crank arms on Ebay for little money. If you want an exact match, it may be more difficult. Make sure you match the length (170mm, 172.5mm etc...) and type (square taper, octalink etc...)
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Old 09-29-11, 04:16 AM   #14
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I found a local shop that had the left crank arm, new, for $18.09 out the door.
Thanks,
Steven
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Old 09-29-11, 07:10 AM   #15
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Great
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