Disclaimer: The following article shows how to modify a set of cranks. Follow the instructions at your own risk. BrainyBiker.com is not responsible for any property damage or accidents that may occur as a result of this conversion.
I have an old Gitane road bike from the 70s. It’s not one of the high-end models, but it has some nice components, and I’ve used it as a donor bike for another build.
One of the parts that I like are the Solida Cranks.
Solida Cranks were not high-end, but I like their appearance. Also, they’re exceptionally light. (A lot lighter than low-end modern cranks.)
Unfortunately, I ran into a problem.
Solida Cranks are a retro French component from the 70s. As such, they have a 14 X 1.25mm thread for the pedals. (It’s written on them.) Subsequently, one can only use them with French pedals from that era.
I have a pair of French pedals, namely, Lyotard 136R, but the pedals ended up too uncomfortable for me, and I had to change them.
I started looking for a way to convert the cranks to a standard pedal thread which is 9/16” x 20 TPI.
14 x 1.25mm indicates:
A 14mm thread diameter (opening) and 1.25mm distance between threads;
9/16″ x 20 TPI stands for:
9/16″ (14.3mm) diameter of the pedal’s threaded part.
TPI is an acronym for Threads Per Inch and shows the number of threads per 1 inch/2.54cm. In this case, the threads’ density is 20 per inch or 20 per 25.4mm which amounts to 1.27mm between threads.
Or in simpler terms, standard pedals have a 0.3mm larger thread diameter than retro French pedals.
If you have 9/16″ x 20tpi taps, you can re-thread the cranks fairly easily.
However, I didn’t have those nor an intention to buy them since I couldn’t find them locally and had to order from online shops and wait for weeks.
Since I knew that I will more than likely never need them again (I have only one pair of French cranks), I got creative and made my one taps.
Here’s how I did it:
- Old pedal axles
- Triangular file
- Wire brush
- Lubrication oil
- Pedal Wrench
Step 1: Take Out The Axles of The Old Pedals
The first step is to extract the axles of old and/or some cheap pedals.
To do that, you will need a pedal wrench and an 11-12mm socket.
The process is as follows: remove the dust cap —> hold the lock nut with the socket —-> unscrew the axle with the pedal wrench. You will also need a flat head screwdriver to unwind the cone and remove the washer.
Once the axles are out, clean them with a degreaser and a rag.
Step 2: Turn The Axles Into Taps
I turned the old axles into taps by getting each into a vise and filing four horizontal deep lines into the threaded part.
I did my best to make the lines equally spaced, but it didn’t quite work out.
To make the cut, I used a triangular file which worked well for the task.
The purpose of creating those grooves is to “sharpen” the axles and turn them into a DIY tap.
Without the cuts, the axle will just force its way in by destroying the existing threads instead of cutting new ones.
Step 3: Clean The Axles With a Wire Brush
The threads fill be filled with small pieces of metal. Clean them via a soft wire brush.
Step 4: Get The Crank That You’re Going to Work On In a Vise
I think that the procedure can be done without removing the cranks from the bike, but I chose to remove them for extra comfort.
I wrapped the cranks in a rag and squeezed them with my old vise. The rag is there to prevent scratches.
Unfortunately, the drive side was a bit difficult to secure.
Step 4: Making The Threads
Note: It is very important to get the direction of the threads right.
For the drive side, use the axle labeled as “R” or right. The “R” axle has a normal thread (right-hand thread) and tightens clockwise.
For the non-drive side, use the axle labeled as “L” or left. The “L” axle has a reverse thread (left-hand thread) and tightens anti-clockwise.
The threading on each side is different to prevent the pedals from unscrewing while pedaling.
Place some lubrication oil on one of the self-made taps and gently screw it into the appropriate crank arm in the direction described above.
Standard pedal axles work as great taps because their first 1-2 threads actually get into the French crank right from the start. This works to our advantage by ensuring that the axle is straight. It’s advisable to do this part by hand.
Once the axle/tap is in the crank, use a pedal wrench to rotate the axle in the right direction.
For every 1/4 turn, I reversed the axle in the opposite direction to clean the new threads from the metal debris. Some people advise doing this every rotation or 1/2 turn, but I wanted to make the procedure extra slow to minimize the chance of failure.
Eventually, you will start to feel medium resistance. That’s fine because you’re cutting metal after all.
Once the entire axle is in, unscrew it gently. You may have to rotate it forward and back on its way out.
Once the axle is out, clean both the axle/tap and the crank threads with a wire brush. Then, if everything is fine, you should be able to screw the tap into the crank by using only your hands.
For me, the non-drive side was very easy to make as it allowed me to comfortably grab it. The drive-side was a bit annoying because the chainrings were preventing me from effectively securing it into the vise.
In the end, it all worked out just fine.
The most likely problems to encounter during this procedure are:
- Damaging the axle threads while filing them
When you start filing the threads, do it slowly and gently. First, get a very small dip into the axle and only then begin applying more force.
- Screwing the Axles/Taps Into The Wrong Cranks
The right axle will be labeled as “R”. It goes into the drive-side crank (the crank arm with chainrings).
The left axle will be labeled as “L”. It goes into the non-drive side crank (the crank arm without rings.)
- Screwing the Axles/Taps In The Wrong Direction
The right axle/tap tightens clockwise.
The left axle/tap tightens anti-clockwise.
There’s always the possibility of cross-threading. To avoid it, make the initial turn without a wrench. Do not rush the procedure. You can even use a square to see if the axle is perpendicular to the crank arm.
FAQ: Am I damaging the cranks by doing this procedure?
If everything goes right, as it should, one is removing merely 0.3mm of metal from the crank. If a crank deconstructs after 0.3mm of material loss, the problem more than likely lies elsewhere.
But if we have to be extremely precise, the crank technically loses some strength, but the percentage is incredibly miniscule (e.g., 0.3%).
I actually measured the old thickness of the cranks and that after the re-tapping.
The before was 9.40mm, the after – 9.26mm. It’s only a 0.14mm difference, but I didn’t put the caliper at the same place both times. In reality, it’s probably bigger.
All in all, the change is too miniscule to obsess over it.
The downsides of this conversion are:
- You will no longer be able to use retro French pedals.
- If you intend to resell the cranks, you will have to explicitly specify that they’re re-threaded as someone may be interested in them to combine them with French pedals.
The upsides of this conversion are:
- Retro French pedals are a rarity. By converting the cranks, you will be able to use a lot more pedals including modern clipless models.
- The conversion is cheap. You can do it by using the axles of old generic pedals. Alternatively, you can buy the cheapest pedals in a shop and gut the axles out. By doing this, you save money and time.
Good luck! I hope this post was helpful.