Bicycle Mechanics - Tap/thread Size for clipless pedals
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05-29-03, 06:16 AM
My son finally convinced me to buy clipless pedals for the Bicycle Ride Across Georgia this year. I have an old Schwinn Continental. Unfortunately when we took off one of the old pedals, we saw that the shaft size on the Schwinn is smaller. Does anyone know what tap size/thread to use. The shaft is evidently 9/16th.
05-29-03, 06:59 AM
According to Sutherland's your old Schwinn cranks probably are probably tapped old USA standard 1/2"x20 TPI. The current standard is 9/16"x20 TPI. You can probably double check this by heading over to Home Depot and try threading a 9/16x20 nut on the pedal threads. Sutherlands offers this tip: When retapping pedal threads, start from the back of the crank arm. Hope this helps.
05-29-03, 07:12 AM
Thanks for the info & taking the time to provide.
05-29-03, 07:40 AM
Glad to help. Welcome to BikeForums! Hang around and ask questions when getting ready for your ride. There is a wealth of experience and friendly advice available here for the asking.
05-29-03, 09:44 AM
I don't think that tapping out your old, forged, one piece crank is a very good idea.
Drilling out the cranks straight and starting the new threads straight is a project that I wouldn't want to attempt using hand held tools. The reason that you tap from the back side of the crank when refreshing pedal threads is to address that very issue. You also have the issue of removing material from where the pedal attaches to the crank arm.
05-29-03, 10:37 AM
Thanks for the iinput. What do you think then? Am I just stuck without being able to upgrade. My son's next focus is a new bike for me that he plans to grow into.
What about going down to a machine shop and asking them to rethread the crankarms, I figure it could not cost very much and would be professionaly done then.
05-29-03, 12:57 PM
Don't forget left handed thread on the left side. That means buying two taps. It may be just as cheap to have a machine shop do it.
05-29-03, 08:51 PM
Rather than going to the effort of trying to make the pedals work, use toe clips and straps(Not something I reccomend often) and save towards a new bike that will probably come with clipless pedals any way and be a joy to ride aswell.
05-30-03, 06:07 AM
The newbie thanks everyone for taking the time to provide information, advice and input. I have plenty to ponder.
05-30-03, 08:07 AM
Up-sizing from the 1/2" to the 9/16" standard not such a great idea. Look at the crankarm, there is not much material there to work with. You may want to simply change out the arms, going with a three-piece bottom bracket. These use cups to down-size the shell to the 1.37" threading for the bottom bracket unit. Look for BMX conversion kits to do this, any good shop should be able to get you more information.
See also One-piece service (http://www.parktool.com/repair_help/ashtabula.shtml)
(On a technical note, tapping the 9/16" thread requires reaming or drilling of the hole. Use a 33/64-inch drill. The current size of the 1/2" threaded hole will be 29/64. Never use the tap to ream the hole.)
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