Indeed; and being skint and untrusting with an aversion to reliance upon others I always strive to keep what I own to stuff I can (at least to some degree) maintain myself. That said while I agree that to work on bikes can be quite simple (again, manifestations of the impure agendas of others notwithstanding) I am sometimes left in awe at what a pure, efficient and elegant device they are from an engineering perspective
Most are supposedly non-reusable. Apparently KMC state that their Missing Link (below) can be re-used 2-3 times; presumably the failure mode is that the little high spots inside the slot wear; potentially allowing the two halves to slide relative to each other and separate when the chain isn't under load.
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My CdF has one of these links and has done about 1800 miles now on a waxed chain; this gets done every 300-350 mile so must have been apart and back together maybe five times with no apparant ill effects. I guess the time to stop using the link will be when it becomes noticeably easy to open and close.
The exception to these limited-use links are the Wippermann items; which are nice in that they can be removed without tools and apparently infinitely reused (although I guess you'd want to the links when the chain's worn out).
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When I got my 10sp bike I bought a new Wippermann 10S8 chain (£20) and a couple of links (£5.50ea); using one link on my existing KMC chain, keeping another as a spare in my cycling rucksack and rotating the chains when one comes off and needs a wax.
I'd planned to do this with the 11sp drivetrain on the CdF, but so far supply and cost issues have put me off. Oddly Wippermann don't do a direct equivalent 11sp chain to the one above, but there's about a 55% hike in price between the 10sp 10S0 (18 Euros) and 11sp 11S0 (29 Euros). Even more shockingly the links are more than double; 7 Euros for the 10sp and 15 Euros for the 11sp
Again I'm not sure if this can be justified on tolerancing / material spec grounds or whether the manufacturers are just taking the pish
I'd not even considered the wear issue being relevant to the chain spec.. I think my Shimano checker does 0.75% wear and is convincingly showing all my chains to be healthy currently. If the wax hype is to be believed they should go on for many thousands of miles.. at some point I'll measure them with a rule to try and put a number on the wear
Apologies to
@gavroche for the thread hijack - got a bit carried away there!