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Brompton folding pedal with aftermarket cranks

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Brompton folding pedal with aftermarket cranks

Old 12-03-23, 02:36 PM
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tcs
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Brompton folding pedal with aftermarket cranks

So as part of a box-of-parts for box-of-parts local swap, I've wound up with a brand new left/right pair of folding Brompton pedals [with Bromfoots (Bromfeet?)].



Well, okay, they're kinda cool so I thought I'd give them a try.

Yeah, no. The top bar won't fit over end of my cranks.



These inexpensive aftermarket cranks are cast (or maybe forged, but I doubt it) in a universal pattern and then they drill the pedal threads @ 170mm, 172.5mm or 175mm. When they make 170s, it leaves too much 'forehead' for the Brompton pedal to fold over.

So to make a short story long, got any crank recommendations here? (And I bet you can guess: something less expensive than the 'authentic' Brompton replacement part.)

Thanx.
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Old 12-03-23, 05:26 PM
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Originally Posted by tcs
These inexpensive aftermarket cranks are cast (or maybe forged, but I doubt it) in a universal pattern and then they drill the pedal threads @ 170mm, 172.5mm or 175mm. When they make 170s, it leaves too much 'forehead' for the Brompton pedal to fold over..
Really, that does not seem to make much sense. They could index the thread hole from the pedal end. That is what I thought they did.
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Old 12-05-23, 03:24 PM
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Originally Posted by Schwinnsta
Really, that does not seem to make much sense. They could index the thread hole from the pedal end. That is what I thought they did.
Should be pretty standard. Maybe your cranks are weird?
On my wife's bike, I replaced her nonfolding pedal with an aftermarket pedal from MKS for standard cranks.
Fit fine. Her old pedal fit my mountain bike with no issues (was just checking for fun)
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Old 02-18-24, 05:10 AM
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I know, slightly stale thread, but not too bad.

OP: I grasp what you are saying; Same crankarm "blank", drilled and tapped at different lengths from BB center, so the "170" length has more aluminum sticking out on the end, pedal won't clear that to fold.

Solution: Find yourself access to a stationary belt or disc sander, or clamp the crank in a vise with padding, and use a hand belt sander; Gently take off the material you need, with coarse-grit belt or disc, with the following cautions:
- USE PERSONAL PROTECTIVE EQUIPMENT (PPE), MEANING, SAFETY GLASSES (GOGGLES EVEN BETTER, TO PREVENT AIRBORN DUST FROM GETTING TO YOUR EYES AROUND THE GLASSES), GLOVES, AND A RESPIRATOR (BREATHING FILTER) THAT HAS A TIGHT FIT ON YOUR FACE, NOT JUST A PAPER MASK, YOU DON'T WANT TO BREATH IN ANY ALUMINUM DUST.
- KEEP A FIRE EXTINGUISHER CLOSE AT HAND, AS THIS MAY GIVE OFF SPARKS. CLEAN ANY SAWDUST FROM SANDER BEFORE DOING THIS.
- If you only need a little off the "corner(s)" to clear, just take off that. If more...
- Leave at least enough radial "thickness" from the threads to the end of the crank arm, as there is on the sides of the arm at the threads. Lay out a scribed line with a compass or around a washer or coin, don't just eyeball it. Layout blue will help, or black sharpie the area before scribing a line, to help it stand out. After sanding, remove sharpie with rubbing alcohol, I think that may work on layout blue as well, can't remember, been over 40 years.
- Go slow on the sanding, frequently pouring cold water on it or dipping it in a bucket, so you don't overheat the aluminum, which will both damage it, and may cause aluminum to embed in the sandpaper. Most cloth-backed sanding belts and discs, should be able to get a little wet, but still, dry the crank arm before sanding again. Take your time, be patient, perhaps don't do all at once. If there is a lot of excess material to remove, you may want to cut most of it off on a bandsaw, either taping over the arm so you can lay the outside of it flat on the bandsaw, or laying it with the outside up, on top of a block of wood to keep it square with the bandsaw blade, then rough sand it to shape.
- Final shaping should be with finer grade sanding, then ideally, polish on a buffing wheel with appropriate buffing rouge.
- Wash crank afterward, taking special note to clean any sanding dust from theaded hole.
- Do NOT use a grinding wheel to do this, big mistake, the aluminum will immediately embed in the wheel, ruining it, unless you can "dress" that surface of the wheel clean by removing wheel material.
- Admire your craftspersonship. Pat yourself on the back for a job well done.

If I had access to a vertical milling machine, I would "contour-mill" it, much easier and faster, then dress it smooth with aluminum files and sanding.

Last edited by Duragrouch; 02-18-24 at 05:20 AM.
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