Boogered Crank Arm Threads
09-10-16, 06:04 AM
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Boogered Crank Arm Threads
I am wrenching on a friend's Bianchi Osprey that has a left crank arm with pedal threads stripped the first few threads. I'm wondering is a tap could come in from the backside to clean up the threads enough to restart the pedal. There are threads good enough to thread the pedal in from the other side but not long enough to grab the starter threads to do any good.
09-10-16, 06:26 AM
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A tap cannot replace stripped-out metal. If the threads are distorted by cross-threading you may be able to clean them up enough to get the pedal threads started, though.
The hole can be retapped oversized and a Helicoil can be used to install new threads which will be stronger than the originals.
The hole can be retapped oversized and a Helicoil can be used to install new threads which will be stronger than the originals.
09-10-16, 07:53 AM
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Of course that's the left hand threaded one, just to be difficult. Could you take the shaft of a junk pedal and grind the face off that would normally butt up against the crank arm. Then it could be threaded in from the back and right through to reshape the threads enough to get the pedal started from the correct side.
09-10-16, 08:08 AM
#4
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Bike Shops have pedal taps for both sides.. to clean up/chase the threads..
Yes pedal thread repairs with steel thread inserts are VG..
Yes pedal thread repairs with steel thread inserts are VG..
09-10-16, 09:04 AM
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Yes chasing the threads from the back side will work good. Crank arms are fairly soft aluminium and chasing from the back will force the threads back into place.
09-10-16, 09:12 AM
#6
Mechanic/Tourist
Even if you manage to clean the thread entry enough to thread in the pedal you will have fewer threads to keep the pedal secure. A Helicoil repair is the best option.
09-10-16, 12:22 PM
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As soon as I get out of work today I'm headed to our shop to have it chased out. Perfect solution for this situation. If the damage were more extensive I would opt for helicoil first and new crank arm second. After this I am picking up the tap for this.
09-10-16, 12:35 PM
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Its a Pair and somewhat unique to the Bike Manufacturing , so get the shop to order your own pair of taps .
09-10-16, 02:03 PM
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09-11-16, 01:32 PM
#10
Hello
coulda just ran the peddle in from the back side
Last edited by zebede; 09-11-16 at 01:34 PM. Reason: oops didn't read full post
09-11-16, 03:53 PM
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