mororian

Two questions here- one, I'm refurbishing a late 70s Motobecane Mirage, and the dust caps on the cranks would not budge from the threads, so I had to break them and take them out in pieces. I was shopping around for new dust caps, but they don't seem to be widely available- any pointers as to where to get them? Preferably ones with a chrome finish, to match the originals.

Second question- I don't know all that much about chains, and there seem to be a bewildering variety. The original one was 1/2 x 3/32, 116 links, which seems to be pretty standard, but then there's different chains for different gearings? I was looking at the KMC Z51, and saw this in the description: "For 6, 7, and light 8 speed use. Compatible with 6-12-18-21-24 speeds." Compatible with 12-speed is what I want, but what does the first part mean? What's the difference between, say, a 7 speed and a 10 speed chain?

dsbrantjr

Chain "speeds" refer to the number of cogs in the rear. The higher cog count chains are narrower; they all have the same 1/2 inch pitch, the rollers and side plates are narrower to accommodate the closer cog spacing.

JohnDThompson 

What kind of crank is it? Most cranks use 22 x 1mm thread for the extractor/dustcap, but in France in the 70s when your bike was built TA cranks with 23 x 1mm thread and Stronglight cranks with 23.35 x 1mm thread were also commonly used.

Any chain designed for 6-7-8 speed use will work. I'd avoid narrower 9-10-11 speed chains, especially with old cranks where the narrower chain might jam between the ring and the crank arm with a mis-shift.

HillRider

Correct for all but the bolded item. The internal width of derailleur bike chains is 3/32" irrespective of the "speed" designation so the roller width is all the same too. What changes, as the number of speeds goes up and the cog spacing gets narrower, is the sideplate thickness and the pin length so the outside width gets smaller.

Here is Lennard Zinn's description:

Tech FAQ: Chain width explained, compatibility queries answered - VeloNews.com

As noted, higher speed number chains have progressively thinner sideplates and the pins have been narrowed to the point they are flush with the outside of the sideplates and the ends flared to rivet them in place. That's why you can't push out a pin to shorten a new chain and push it back to rejoin the ends. It leaves a weak point since the pin is no longer riveted. Current chains (7-speed and above) must be joined with a specific joining pin (Shimano and Campy) or a master link (KMC, Wipperman and SRAM)

mororian

Well, I've been doing a bit more research, and it turns out that this Mirage is actually from '83. It's a Stronglight crank, but a number of sources I've seen claim that they standardized their threading in '82, so I believe it would be 22 x 1.

SlowJoeCrow

On modern stuff I just use the capless bolts like these FSA parts https://www.universalcycles.com/shop...06&category=63 instead of trying to find and keep dust caps. For French stuff with odd extractor sizes a self-extracting crank bolt is an even better idea since once they are installed all you need is a big enough hex key.

JohnDThompson 

Yes, a post-1982 Stronglight crank should have standard thread. In which case, something like this ought to work:



Sunlite Crank Dust Cap CP Bike | eBay

HillRider

If it is a standard 22x1 cap, check with some older bike shops. They might have a bunch lying around in their "misc crap" drawer and would be happy to give you a pair.