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Chainline weirdness with fc-m460 square taper chainset

davee128davee128 Posts: 26
edited April 2017 in MTB workshop & tech
So I have a 2005 vintage Specialized with 68mm BB shell that I bought 2nd hand. It came with BB and cranks (Deore m460). I believe the cranks were original to the bike when new. No idea about the BB but the axle length was 117.5mm. I replaced the BB when it died, with a 118mm as that was all that was available. The front mech I've been using was a circa 1995 Alivio. It's never been 100% reliable shifting to the granmy, but has been ok most of the time with the limit screw out at max (only just making contact).

I tried to upgrade the ancient front mech to a 9 speed deore triple in the hope of getting better shifting and found that it wont go anywhere near the granny!

Investigating this I found that the chainline is way off. Having trouble measuring it accurately, but I find that the chainline is below 45mm.

The cranks have never come loose so I'd be surprised if the taper was knackered.

Any ideas why?!

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