Retapping French threaded cranks
 

Has anyone ever tried re-tapping french pedal threaded cranks to english (using actual taps, not pedals)? This may have been covered, but search does not work well on my Blackberry.

Thanks

The French threads are 14 X 1.25mm and can be retapped using a 9/16" X 20tpi tap with no issue.

Yes, it's pretty straight forward. You'll want to use sharp taps, not ones that have been used to chase threads for years. Most important part is to go in square or you'll end up with a wobbly feeling pedal. Check it with a good square on all sides as you start, having the arm clamped to a flat surface will help as well.

Just did this 45 minutes ago. Use oil, it's easy. Be careful to get the tap in straight. I did it on stronglight 93's.

You just missed a discussion:

http://www.bikeforums.net/showthread...Threaded-Crank

Someone has retapped French cranks using pedals?

Regular threads are not intended to cut material, so I do not believe that un-modified threads would stand a chance. It is possible to take a hack saw and file to the pedal threads and modify them. Take a look at a self tapping screw to see what needs to be done. However, it would be a large pain in the butt and much easier to simply buy the taps. You could also explore sending them off to have them done (local bike shop?)

Tom

In a pinch, you can use a hard bolt, by comparison, to chase, not cut, threads in a softer metal.

Take and old left pedal and an old right pedal, ones that you will not use again. Using a very find blade hacksaw, cut a slot or two or three equal distance from each other. The slots run parallel to the center line of the bolt.

Now, using lots of lubricant, thread the correct pedal spindle into the correct crank arm. In a wee bit, back out to clear the groove, and in a wee bit more.

That's how one chases threads when there is no proper thread chaser, or tap(s) to be had.

^^^^^ This is old school for sure:thumb:.... Being an automotive technician by trade, I've done this many times in the past 35 years when at a loss for a needed tap, and it works. I do however suggest a practice run on something other than your cranks before diving in to your beloved crank using this method. This is how us old guys did things back in the day;)......

You won't find a bolt with the correct 9/16" X 20 threads. You'll only find bolts with 9/16' X 18 threads. Pedal threads have a unique pitch, so what are you talking about?

Perhaps a sacrificial spindle from another pedal?

You use a pair of old pedals as the self made tap..... Everyone has a pair of junk pedals lying around.

Using pedal taps is the only correct way to do it. They're not that expensive and you can help out your friends. I've tapped more of other people's cranks than my own.

Have taps
Have cutting oil (aluminum even)
Have machinist square
Have vice with leather jaw covers
Have Stronglight cranks with french threads
Have a white Ford Econoline Van name "Vincent" (van go...spelled per my 4-year-old)
DO NOT have french threadded pedals I care to use on the Mercian build

One of these things in not important

I don't think you could get the tap started crooked even if you tried really hard. It threads right in and just removes a little bit of material. Fourteen millimeters and 9/16" are very close. You don't need special cutting oil for this. Any oil will do. In fact, no oil at all will do.

[QUOTE=Grand Bois;12258007Any oil will do. In fact, no oil at all will do.[/QUOTE]
True, dish soap will do. That said, use oil.

Two sacrificial spindles, one right hand thread and one left, right? And that is exactly what I meant, except in industry, I rarely had to chase the threads on a bicycle pedal.

I'm afraid you're wrong there, old boy. I managed to do exactly that on a 1950s NOS Stronglight 49D. The crank side worked fine. I still regret it. The local engineering shop says they can repair it for $60 but I'm hesitating...