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JB Weld pedal-to-crank arm experiment
#1
Hey guys,

So as I mentioned in a previous thread, I had threaded my crank arms while screwing in my shiny new pedals into my ‘01 Norco wolverine. Being relatively new to mtbing, I started researching my options on the fix. Obviously, buying a new crank and arms was the most reliable and safe fix but being damn inpatient I wanted something to remedy the problem NOW. That's when I came across the famous JB weld idea. “gluing” my pedals on?! I was unsure of that... and with some reading I found that there are alot of opinions out there about the use of the epoxy on pedals and crank arms (and on bike repairs in general) but there was not alot of information on actual successes and failures. After ordering my new crank, arms and pedals, (I decided to go against using a chemical bond as my actual repair because of the stress put on the contact point of pedal to arm) I decided that while I wait for my new parts I'd see just how well JB weld would hold up once and for all. This was my JB experiment.

1. My pedal holes in the arm were reamed out. Barely any threads left and the pedals fit in loosely. (don't ask...) The pedal holes weren't completely smooth though, so I figured the JB had at least a rough surface to bond to.

2. I used the original JB weld.

Day 1 - 7:00p.m - took my pedals and wiped down the threads with a cloth sprayed with a SMALL amount of finish line degreaser. Wiped down with dry cloth and let dry. I then did the same to the pedal hole on the crank arms as well so no other oil/grease would mess up my bond.

9:00p.m - mixed the JB weld products 1:1 as per instructions, and applied generously to pedal threads and crank arm holes. Then I placed the pedals in and made sure they were sitting proper to harden in.
So far so good....

Day 2 – 9:00p.m - I figured why not I'll give it another day of curing to make sure those peds’ are hardened in to their absolute full potential . I’ll give them a total of 48 hours (JB says to wait 24 hours) to set before putting my weight on the bike. I mixed up another batch of the JB and reinforced my drive side pedal connection by giving it another coat. Just to see...

Day 3 - 9:30p.m - I take my bike outside and inspect my job. I put hand weight on the pedal. I stand on it. I then jump on it. It looks good actually and feels strong and I am somewhat confident in the bond. I take it for a spin up my somewhat bumpy street.

9:40p.m - My drive side pedal falls off, and with enough stress of uphill pedaling, the other pedal breaks free eventually. Surprised?

So in my conclusion, if you are thinking about using JB weld for this repair, it’s a waste of time/money and a safety issue. I’m sure JB has other uses but bike repair should never be one of them. There is just too much shear stress on the connection that no epoxy would ever do in my opinion. I’m sure I applied it properly too. And believe it or not, one of my local LBS actually recommended I repair my pedal this way?!
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#2
(07-06-2011, 09:42 PM)Wolfie Wrote:  . . . So in my conclusion, if you are thinking about using JB weld for this repair, it’s a waste of time/money and a safety issue. I’m sure JB has other uses but bike repair should never be one of them. There is just too much shear stress on the connection that no epoxy would ever do in my opinion. I’m sure I applied it properly too. And believe it or not, one of my local LBS actually recommended I repair my pedal this way?!

I have heard from other weldors that JB Weld doesn't work as well as regular welding. Never used it myself though, but thanks for the honest critique! Smile

Steve
Junkyard Tools rescued from the junkyard!
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#3
The main issue was the loose fit. If you had a tight fit (jammed tubing as a shim for example) so that all the epoxy was doing was preventing the pedal from coming out sideways, rather than taking the alternating compressive and tensile loads (due to the loose fit); it would have probably held.

Epoxies and other adhesives are designed to work in shear, they are not very good in alternating tension and compression - they have very low fatigue strength.

Yes; I design adhesive joints for a living.
Nigel
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