To my amazement a Sachs-Sedis chain will absolutely not exceed 0.5%
stretch after more than 5000mi, despite some hills where one has to
stand in the pedals. Never had a chain last this long. However, the
rollers have developed a lot of play, about 0.040" or 1mm. How much is
too much? I guess it's almost finished because of those rollers.

Getting older, I'd like to increase the large cog to at least 40T from
my current 32T. Of course, that will require me to retire the trusty old
Shimano 600 derailer. I don't want the cassette to become ever wider and
also need to maintain 7-speed spacing so I can use the more robust
old-style 7.3mm pin length chains such as KMC Z50 (can't find the Sachs
anymore). In the past I hacked cassettes, installed the cogs I wanted
and re-used the old spacers. Can the larger cassettes like in the link
below still be hacked apart? I don't mind drilling or dremeling stuff to
get them apart. If memory serves me correctly I've installed a Shimano
STX-RC freehub on the road bike after the last UG freehub had croaked.

https://www.ebay.com/itm/SunRace-CSM...k/132325285327

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Regards, Joerg

http://www.analogconsultants.com/