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I removed the pedals of a Göricke bike from 1934 or 1935 (according to the bike number). It has a Glockenlager (What is that in English? Bell shaped bottom bracket?) as seen in the picture. The crank threading for the pedals however is quite messed up and I would like to re-cut it. I measured 4 threads at about 4,8mm (or 4,9mm) with an 14,2mm external diameter on the pedals. The diameter is a tipical 9/16 pedal threading, but the thread steapness only results in about 20-21 threads per inch, and not 24. 24 is the normal amount of threads per inch for pedals.

EDIT: I noticed 20 tpi is normal and not 24 tpi. Therefore it should be a normal threading.

Is this some other threading they used in these days or shall I just cut it with a normal pedal thread cutter? The pedal make is K&B (the logo is in a cloveleaf) Bottom bracket

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It may be "old French": sheldonbrown.com/gloss_p.html#pedal –  Daniel R Hicks Mar 17 '13 at 13:30
    
If you go to a decent machine shop, they can measure the pitch/depth/diameter/threading of anything - that'd be your safest bet considering the age of the bike. (In fact, if they are good they'll likely have taps and dies to fit it.) –  WTHarper Mar 17 '13 at 13:59
    
Thanks for the ideas. It might actually be a normal thread. It is fatter than 14mm, more like 14,2mm, therefore it can't be French. After measuring again it could be 20 tpi. Somehow I though 24 is normal, but it is actually 20 tpi. Some shop was selling 24 tpi drills, that must have thrown me off. Because I can only there 4 threads it isn't very accurate, but I will just try my luck. –  Franz Kafka Mar 17 '13 at 16:54
    
If you try threading the wrong size tap into your crank, you run the risk of cutting out the original threads. If you can't get a hold of a pitch gauge, look into heli-coil or some other sized thread repair slugs for pedal threads (if you do indeed cut out those out threads.) –  WTHarper Mar 17 '13 at 23:30
    
I don't know much about old cycles and have limited knowledge of German but I do know 'glock(en)' pertains to bell(s) and 'lager' in a technical sense is bearing The Germans love compound nouns so this could be the translation you are looking for. Sorry I can't shed any light on the engineering side of this topic –  stew Apr 25 '13 at 7:34

1 Answer 1

Just try chasing the threads with the normal taps (remember the left side is reverse threaded) then try the pedals. Sometimes just chasing and cleaning will be enough, and what have you got to lose if the threads are already damaged. Some pedals have a longer section of thread than others, certain pedals may work better or contact the intact threads better.

Otherwise there are insert kits that cut a larger diameter hole then insert a brass threaded part that has normal pitch threads on the inside. These kits are expensive and may only be made for aluminium cranks so check that out first.

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