Chainset weirdness

Good thing I went further down the board than usual because of the
mindless helmet flame-thread, or no one would have seen your post!

To answer your "Q", if you have an old fashioned BB, with seperate cups
and spindles, then the extra distance in the lefthand crank is probably
to offset the additional distance the right one sits out because of the
additional thickness of the sprockets.

To check this, measure the distance between the crank ENDS (the pedal
end) and the chainstays when each arm passes. They should be nearly the
same if I'm right.

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Rob said:

I own an old specialized rockhopper from about 1994. The original
chainset was an alivio that used a bottom bracket with 110mm
square taper spindle and 78mm shell.

Do you mean 68mm or 73mm? Specialized changed at some point in the mid
nineties. My '92 Stumpjumper uses a 68mm, while my later ('98?)Rockhopper
uses 73mm.

Quoted message said:

About a year ago the alivio was giving up the ghost, so I managed to
locate an LX chainset that must have been one of the last ones produced
for square taper spindles. I think stamped as FC M589.

Probably a 569.

Quoted message said:

When the LX chainset was fitted, I discovered that the end of the
lefthand crank was 5mm further away from the frame than the righthand
crank. A very unsymmetrical situation. Recently I refitted the alivio
chainset as an experiment and confirmed that the cranks were the
same distance away from the frame, as they should be.

So, howcome the Lefthand LX crank doesn't fit as far onto the spindle
as the alivio?

It probably does, but the LX crank will have a broader flare, putting the
end of the crank further from the centre line of the bike when used on the
same BB.

Quoted message said:

Is the lefthand LX crank defective?

Unlikely.

Quoted message said:

Do I need a different kind of bottom bracket? I tried a 113mm spindle
length, but this just messed up the chainline.

A 107mm BB has 3mm less offset on the left, which will get you close to
symmetry without affecting chainline. Unless you have an e-type BB, the
other possibility that springs to mind is that maybe you have a 73mm unit
in a 68mm frame, but that's unlikely if the bottom bracket you currently
have is original to the bike.

James Thomson

right - one spindle side is longer than the other - check the LX - are
there marks on one side or two circumferential rings on one side but
not the other? the marked side is longer from center outward to the end
than the non-driveside

Further investigations have shown that the new left hand crank (LHC)
does seem to fit onto the spindle the same as the old LHC. This seemed
odd. Placing the two LHC's on a flat surface so that the "flare" of the
LHC's is away from the surface it became apparent that the new LHC
flares a further 4 or 5mm than the old LHC. This is what seems to be
the problem.

I will try a 107mm BB in my LBS to see what happens. If this works,
does it mean that different chainsets require different spindle
lengths? If so, then how do I know what to get?

The marking for the new CS is FC M569. ( I had it wrong before) and
it's a square taper LX CS. the old CS had 175mm arms, the new CS has
170mm arms which is better for me.

My bottom bracket shell is 73mm. Measured with my vernier calipers.

Thanks for any advice supplied, past or future.

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In article <[email hidden]>,

Rob said:

Further investigations have shown that the new left hand crank (LHC)
does seem to fit onto the spindle the same as the old LHC. This seemed
odd. Placing the two LHC's on a flat surface so that the "flare" of the
LHC's is away from the surface it became apparent that the new LHC
flares a further 4 or 5mm than the old LHC. This is what seems to be
the problem.

I will try a 107mm BB in my LBS to see what happens. If this works,
does it mean that different chainsets require different spindle
lengths?

_ Yes. Things are more standardized now than they used to be, but
this has always been true.

Quoted message said:

If so, then how do I know what to get?

_ If you are lucky enough to have the installation instructions
for the crankset it will tell you want BB to get. If not
there is always Sheldon Brown's website[1] with the BB/crankset
compatiblity page.

_ If all else fails, there is almost always a Phil Wood BB that
will work. These are pricey, some people don't think they are
worth the extra money, but they making solving problems like
this much simpler.

_ Booker C. Bense

[1]- Finding this page w/google is left as an exercise for the
reader...

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