classic crank threads
 

I have a late 70s classic with Campagnolo components. The original Campy pedals mount easily on the Campy cranks, but I can't use them (too small). When I try some current pedals, I find some thread on cleanly and others just don't want to go. For example, I have a pair of MKS Sylvan touring pedals of which the right one installs nicely but the left meets heavy resistance halfway in. There's no junk in the threads getting in the way.

I suppose a good shop would have taps (left and right threaded) that might be used to clean up these threads. I find it strange though that the orignal pedals go on easily.

Have threading standards changed, or were threads just not as accurate back in the 70s?


[update] I cleaned out the crank threads (again), put TriFlow on the MKS pedal threads and cranked them in with a sizeable pedal wrench. They didn't seem to be as happy about it as I would like, but I blew past the resistance and they threaded in all the way. Just a question of accuracy in the machining of either the cranks or the pedals I guess.

Yeah, I don't think pedal thread standards (9/16"x20 tpi for good quality bikes) have changed for many decades and AFAIK, there aren't any differing ISO/JIS type standards either. The fact the right MKS pedal went in with no difficulty says the pitch and diameter are the same as your older Campy pedals.

As Hillrider said, there has only been one standard in use throughout the world (except France (figures)) for many decades. However even within the same standard there is tolerance, so there will be some variation in fit. When Campagnolo started aluminum cranks they elected to keep the thread nearer to the lower size limit (as did other alloy crank makers) to ensure a tighter fit. It makes sense because aluminum threads have less strength than the same threads in steel, so good fit is more important.

Odds are that your other pedals have slightly larger pitch diameters (how to measure) and so are just that extra bit too tight. I suggest you check that there are no dinged threads, and if not, grease them and gently force them in. Don't get carried away, and if the force needed is significant, or ramps up as you go deeper, stop.

It's barely possible that your Campy cranks were made for the French market and have the 14mm thread rather than the BSC/ISO thread.

Well, the OP said the right side pedal threaded in with no resistance or problems so I expect the threads are the correct configuration and the left pedal problem is just tolerances.

As I updated above, I got them in and I don't think there was any damage in doing so. I've actually installed a different pair of new pedals in those cranks before without this resistance. So yes, I think it's just tolerance and materials.

I agree, but when I tell someone I don't know, to force something I didn't see, I always try to give them a reason not to go crazy.

No, there was an Italian pedal thread. It's, in true insane italian fashion, 9/16" X 20 tpi, with, like you'd expect, Whitworth thread form. 55 degrees, rounded roots and crests, instead of the 60 degree thread that everyone else used. A tap, or just a bunch of force, will get them to take a standard pedal.

OP: examine your original pedals; if they're Italian threaded, there's a good chance they'll say "D" on the right one, and "S" of the left.

+1. I have a set of Campy cranks (de-anodized and polished Campy BMX) that I used with Shimano clipless pedals for many years. The pedals were always tough to install and remove- they were impossible to thread on without a wrench. I never saw any damage in the threads of the cranks so they're probably OK.