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stripped thread on crank

Old 05-15-17, 07:55 PM
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mrclean167
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stripped thread on crank

my left pedal stripped the threads on the crank...is there a shim repair kit i can purchase?
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Old 05-15-17, 08:17 PM
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for the left crank arm
it is cheaper to just replace the crank arm itself
that's a 20$ part

while the Helicoil re-threading operation to repair the damage, is usually a 30$+ repair

The Right Crank arm, with the sprockets attached is a different story, that one costs more and is worth the repair.

Just buy a new left arm; make sure its the same length and direction (square hole, vs diamond hole)


And Next Time you buy a bike Online and assemble it yourself, Don't. There's a reason you're supposed to have a shop do it.
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Old 05-15-17, 08:35 PM
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You can have a helicoil insert installed to repair the damaged threads, but because of the cost of the repair, it might be cheaper to replace the crank arm. It depends on how expensive your particular crankset is.

As for whether or not you should have a shop assemble your bike... It depends on your mechanical experience and aptitude. And even if you don't score well in those departments, feel free to turn your own wrenches if you enjoy doing it (and can afford to deal with the mishaps).
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Old 05-15-17, 08:35 PM
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Originally Posted by mrclean167 View Post
my left pedal stripped the threads on the crank...is there a shim repair kit i can purchase?
Depending how stripped they are, find out the size of your threads and buy a thread tap, use it to chase the stripped threads and you might get lucky and fix them. You should get a new set of pedals though regardless because the repaired threads will most likely cross using your old pedal.
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Old 05-16-17, 10:51 AM
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Originally Posted by Scooty Puff Jr View Post
Depending how stripped they are, find out the size of your threads and buy a thread tap, use it to chase the stripped threads and you might get lucky and fix them.
The left side crank arm uses a bicycle-specific 9/16" x 20tpi left-hand thread; purchasing this tap for a one-off job is unlikely to be cost-effective. The right side arm uses 9/16" x 20tpi right-hand thread, which is a common spark plug thread.
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Old 05-16-17, 11:34 AM
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Originally Posted by JohnDThompson View Post
The left side crank arm uses a bicycle-specific 9/16" x 20tpi left-hand thread; purchasing this tap for a one-off job is unlikely to be cost-effective. The right side arm uses 9/16" x 20tpi right-hand thread, which is a common spark plug thread.
Ahh, you are correct sir ! I forgot all about that being a left handed thread, thanks for correcting me.
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Old 05-16-17, 12:19 PM
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Originally Posted by JohnDThompson View Post
The left side crank arm uses a bicycle-specific 9/16" x 20tpi left-hand thread; purchasing this tap for a one-off job is unlikely to be cost-effective. The right side arm uses 9/16" x 20tpi right-hand thread, which is a common spark plug thread.
Do Australian spark plugs turn the other way?
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Old 05-16-17, 11:15 PM
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Originally Posted by JohnDThompson View Post
The left side crank arm uses a bicycle-specific 9/16" x 20tpi left-hand thread; purchasing this tap for a one-off job is unlikely to be cost-effective. The right side arm uses 9/16" x 20tpi right-hand thread, which is a common spark plug thread.
Or you can get your local shop to do it for $10.
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Old 05-17-17, 08:34 AM
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Originally Posted by JohnDThompson View Post
The left side crank arm uses a bicycle-specific 9/16" x 20tpi left-hand thread; purchasing this tap for a one-off job is unlikely to be cost-effective. The right side arm uses 9/16" x 20tpi right-hand thread, which is a common spark plug thread.
For just chasing threads, take an old set of pedal spindles, grind a flat on one side of the threads and use those. May not work as well on steel Ashtabula cranks, but I'm not sure I've ever seen a steel 3-piece, and the pedal threads are definitely hard enough to chase threads in aluminum cranks.
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Old 05-18-17, 09:38 AM
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Originally Posted by JohnDThompson View Post
The left side crank arm uses a bicycle-specific 9/16" x 20tpi left-hand thread; purchasing this tap for a one-off job is unlikely to be cost-effective. The right side arm uses 9/16" x 20tpi right-hand thread, which is a common spark plug thread.

I just hope no one goes out and chases their sparkplug threads with this "common" size. It's close to 14mmx1.25 but not interchangeable. We haven't used fractional size sparkplug threads since the 30's. The standard is metric available in a few diameters and TPM.
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