Boneheaded question about Shimano chainrings

[Matt Barmack]

As with most of my efforts to maintain my bike, this most recent one
has ended poorly. I removed my Dura Ace chainrings to get at some
well hidden grit, but I forgot how they went on the bike. I already
know from trial and error that I got the smaller of the two, the 39,
wrong the first time. The big one seems OK, but I am not sure that it
is right. There is some kind of small post protruding to the outside
of the ring, i.e. away from the bike. I don't know whether this is
intended to prevent the chain from coming off to the outside or to
help with shifting, in which case I probably put the big ring on
backwards. Any guidance would be appreciated.

Thanks,

Matt

[Mike Jacoubowsky]

Matt: First, make sure the 39t (inside) chainring has the indented side of
the chainring holes facing towards the inside. That's a recess for the
chainring bolt head. On the larger chainring, that recess goes to the
outside, facing away from the bike. For orientation, each of the chainrings
should have a little triangle (sometimes a little extension out from the
chainring, shaped like a V), and this is lined up with the crank arm.

--Mike-- Chain Reaction Bicycles
http://www.ChainReactionBicycles.com

"Matt Barmack" <mbar...@alum.mit.edu> wrote in message
news:84242d33.02033...@posting.google.com...

[Spooky]

The protrusion you mention lines up with the crank arm.. it's to stop
the chain droping between the ring and the crankarm should the chain
'overshift' off the large ring

On the smaller ring, line up the small triangle on the ring with the
crankarm

[Weiwen]

www.shimanoeurope.com should have the diagrams online.

"Matt Barmack" <mbar...@alum.mit.edu> wrote in message
news:84242d33.02033...@posting.google.com...

[Matt Barmack]

Mike,

Thanks for your reply. That was my intuition, but when I installed
the small chainring with the indentations in the bolt wholes towards
the frame, my drivetrain was very crunchy. I am guessing that the
small ring was installed incorrectly when I bought the bike and is now
worn in the "wrong" direction. It has never bothered me before. Any
major issues with installing a chainring backwards?

Best,

Matt

"Mike Jacoubowsky" <mik...@pacbell.net> wrote in message news:<BAUp8.4517$yU1.330...@newssvr21.news.prodigy.com>...

[Mike Jacoubowsky]

On many cranksets, the inside chainring is designed with teeth that have an
offset to one side, to preserve the correct distance between it and other
chainrings. Reversing it may either cause the chain to scrape on the large
chainring (when in the small chainring) more than it should, or perhaps
allow the chain to drop in-between the two chainrings.

--Mike--
Chain Reaction Bicycles
http://www.ChainReaction.com

"Matt Barmack" <mbar...@alum.mit.edu> wrote in message

news:84242d33.0204...@posting.google.com...

[Matt Barmack]

Mike,

Thanks again for your reply. I found the Dura Ace manuals that came
with my bike and I also checked my wife's bike with Ultegra, which
presumably is similar enough.

I have one nagging question which probably just reflects my continued
confusion. When I orient the triangular mark on the small ring with
the crank arm so that it is visible, as the manual instructs, i.e. so
that it faces the bike rather than the big ring, the recesses in the
bolt holes face the big ring so that they seem to serve no purpose.
Am I losing my mind? Your original advice to position the recesses in
the bolt holes on the big ring away from the frame seems to make sense
and is consistent with the manual.

Best,

Matt

"Mike Jacoubowsky" <mik...@pacbell.net> wrote in message news:<70vq8.2191$nJ1.101...@newssvr14.news.prodigy.com>...

[Mike Jacoubowsky]

Yes, the recesses should serve a purpose, and that purpose is to accept the
back end of the chainring bolts. The visible triangle shows to the inside
of the crank, not the outside.

--Mike--
Chain Reaction Bicycles
http://www.ChainReaction.com

"Matt Barmack" <mbar...@alum.mit.edu> wrote in message

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