Chicago Al 

My Motobecane Grand Record is nearing completion and I took it out for a spin today. It came to me with the clearly original Atom 700 pedals, on TA Professional (3 arm) cranks. I had everything apart for cleaning, etc. The crankarms had a bit of wear around the pedal openings, apparently from the pedals having been overtightened, but otherwise they looked fine.

As I put together the bike I thought I'd try other pedals, and a pair of Maillard 700 platforms were handy. The Atom pedals appear to be English thread as they are marked R and L; also nothing else on the bike is actually French thread, it's an export model.

The only French pedals I have are clearly marked D(roite) and G(auche). And actually those aren't French pedals but SR from Japan, but were on a PX-10 with Stronglight cranks...so Japonaise.

So the Maillard pedals, also marked R and L, threaded in easily, and I was off for a ride. They felt okay, but I have another pair of pedals I thought I'd try this afternoon, SR PD-11s, a knockoff of the much loved Marcel Berthet platform style. They're also marked R and L...and they won't thread on. Rather, they'll do a bit of thread and then get very tight. Of course I'm not going to force them.

Now it gets strange. Because I went back to the Atom pedals, original to the crankset, and they now feel the same. They won't go back on.

The Maillards fit on again just fine, actually I can thread them on with my fingers. Now I brought out the other SRs, definitely French, and they fit on too, a bit loosely. Which is how they should feel in an English threaded crankset, right?

I know that English pedals, being very slightly larger or more coarsely threaded, can be forced onto French threads and they'll essentially tap themselves (not well). But the reverse can't happen, can it? Did I somehow go from English to French?? I wouldn't have thought the Maillard pedals were French...but maybe they were? (I don't have the Stronglight crankset anymore or I'd use that as a comparison.)

Any suggestions?

I'm not forcing anything until I figure this out!

rhm

Damage to either pedal threads (not likely; it's hardened steel) or the crank arm (more likely, being aluminum) can cause this. But that's not necessarily your answer.

A couple weekends ago I had some guests and we wanted to change the pedals on the TA cranks on my Cera so Justin could ride it with his own pedals; and they wouldn't go on. I have some Nashbar SPD's on there that fit fine, but Justin's Shimano SPD's did not fit and we did not force it. I don't know why they wouldn't go. We took the Nashbar pedals out, tried (and failed) to put the SHimanos in, then put the Nashbars back in. Clearly there was no damage to the crank; but the Shimanos did not fit. Like you I cannot explain it.

auchencrow

Silly question, but do BOTH original Atom pedals now not want to thread in, or just one?
If it's one side or the other I would suspect a burr.

Chicago Al 

Actually that's a good question, Auchen. I was concentrating on one side but tomorrow will check the other. For sure the SP11s didn't want to go on either side.

I went back and did try some very *gentle* force on the Atom on the L side, figuring that it HAD to go on, and it did, but only with the pedal wrench. No sign of aluminum being cut. Maybe just lack of precision in machining? The Maillards can be threaded on by fingers, the 'known' French SRs easily thread on with fingers and are noticeably loose until the threads bottom out.

Trying to measure the width of the pedal threads with digital micrometer, on the 'flats' of the micrometer...hard to get an even reading, but looks like:

French SRs: 13.7mm

Maillard: 13.9something mm

SR SP-11: 14mm

Atom 14mm

Random extra SR: 14.1mm

So possibly the Maillard is just on the small side of English.

rhm

In the case I described, both Shimano pedals were reluctant to thread into the TA crank while both Nashbar pedals were perfectly willing.

unworthy1

I think you have experienced what in the engineering game is called "tolerance": there's a range of sizes that will pass inspection/ measurement/ testing, and it can result in poor fit when one part is at the one end of one manufacturer's tolerance, and the mate is at the other extreme of some other (or the same guy's) tolerance.
Keeps things interesting...

big chainring

Pedal threads on cranks can get weird over the years. I have a TA crank and changing pedals is always a dodgy thing.

The wear around the pedal opening on the crank may be where pedal washers may have sat. The French were big into pedal washers.

Chicago Al 

Pretty sure you guys are right, its a matter of tolerance. On the drive side I threaded in the French SR, which stayed rather loose, then the Maillard, an easy fit, then with the pedal wrench the Atom. The SR PD11 resisted too much, I didn't want to force it. Yet with the micrometer the Atom and PD11 are the same size. My guess is that the crankset is actually a bit smaller than spec. So no room for slight differences in the pedals.

Not too surprised at this, I started a thread in the mechanics forum about the dubious finish of the TA cups in the BB.

But..I'll put those pedals on another bike, and in general I like the Motobecane very much.

teetime

Pro tip:

You can try to thread in from the rear, with plenty of oil, to clear the threads.

Failing that, re-tap the threads before you ruin it.

Chicago Al 

I'll try that, thanks...never thought to try it from the rear.

I mean...oh, never mind.

Also a friend could retap the threads if necessary, I know he has the right tool.

Oh boy. I give up!

Chombi

I think I am experiencing the same "problem" with my Topline crankset. I first tested Maillard quill peds on it and it threaded in almost all the way mostly by hand, but when I try to screw in MKS quill pedals into the Topline cranks, it stops threading in easly about mid way into the threaded holes. Looks like I can screw it in all the way with a pedal wrench, but the amount of building resistance worries me that I might damage the threads on the crank if I do so, so I didn't go through with it for now. Weird thing is, both Maillard and MKS pedals easily threads into the 1st gen DA crank I have on one of my bikes. I'm thinking that the finish on the threads of the MKS pedals (chrome?, which the Maillard pedals do not have) might be making it tighter to screw on to some cranks with tighter tolerance cut threads?? Should I go ahead and screw in the pedals into the Topline cranks all the way? Would I be in danger of possibly cross threading or stripping the threads if I wrench (with the neccessary substantial toque needed) them in??

Chombi

Jeff Wills

I've had the same problem putting Shimano pedals on Campy cranks. (Save the hate mail for later!) IIRC, the thread is the same, but the thread profile is a little different. This causes resistance when installing "Japanese" pedals on "European" cranks.

Chicago Al 

Reviving this thread to note that I took my Motobecane by my favorite old-school bike mechanic's house today. He has a great love for old French and English bikes, and a tool collection to match. First step was to confirm what everything was. The Maillard pedals fit the French thread profile on his set of gauges almost as well as English, the SR pedals fit the English, not the French so well. He chased the pedal threads on the TA cranks with a VAR tool, which did remove a bit of metal but only a bit, and afterward the SR pedals threaded in snugly but without a problem. I did a test ride with the pedals, FWIW, and think they're going to work out nicely. I'll keep my eyes open for a pair of the Lyotard 'Marcel Berthet' (Englsh thread!) but until those turn up at the right price these may do perfectly well.