Bottom Bracket/Chain Line Woes
#1
thanks Karl Von Draise
Thread Starter
Bottom Bracket/Chain Line Woes
So i just bought a used steel framed road bike, made in oakland ca. by a guy named mikkelsen. Its from 1993 with a mostly complete Campagnolo c-record group. It has a sachs new success rear derailleur and im told a phil wood bottom backet. After a series of measurements i have determined the front chain line is 48.38mm which is about five mm off of what it should be according to shimano which specifies a 43.5mm front chain line for bikes with a double chain ring.
I have adjusted everything else the best i can and i feel the chain line has to do with the shifting problems i am having, (it sounds kind of like the chain is binding or rubbing when i torque it up hill on the small chainring and the biggest three cogs, and if im in the big chainring it sounds like the chain is rubbing on the adjacent cogs in the rear on any of the three smallest cogs and on the biggest cogs, as is expected for those) So i have limited gear choices in addition to having a eight speed cassette already.
So my question is what are my options to fix the problem? I only have experience with overhauling Loose/caged ball BBs, which dont have lateral adjustment ability. Do cartridge BBs have the ability to adjust out the 5 mm i need to move the drive side crank in? Do i need a new BB? How do i measure for the correct length? Thank you in advance for your wisdom
I have adjusted everything else the best i can and i feel the chain line has to do with the shifting problems i am having, (it sounds kind of like the chain is binding or rubbing when i torque it up hill on the small chainring and the biggest three cogs, and if im in the big chainring it sounds like the chain is rubbing on the adjacent cogs in the rear on any of the three smallest cogs and on the biggest cogs, as is expected for those) So i have limited gear choices in addition to having a eight speed cassette already.
So my question is what are my options to fix the problem? I only have experience with overhauling Loose/caged ball BBs, which dont have lateral adjustment ability. Do cartridge BBs have the ability to adjust out the 5 mm i need to move the drive side crank in? Do i need a new BB? How do i measure for the correct length? Thank you in advance for your wisdom
#2
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 38,658
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Mentioned: 140 Post(s)
Tagged: 1 Thread(s)
Quoted: 5762 Post(s)
Liked 2,535 Times
in
1,402 Posts
If I remember Phil bottom brackets of that era. neither lockring had a shoulder so you could walk the BB cartridge a few millimeters to either side of the centered position in the shell. If it's already as far to the left as possible, then you need a new cartridge with a shorter spindle.
Note that chainline calculations depend on the cassette width and axle width. Since you know your chainring centerline, check your cassette's, by measuring from the inside of the right dropout to the center for the cassette and subtracting that from 1/2 the axle width. ie. 130/2 -17mm = 43mm. The goal is to have both chainring and cassette chainline offset equal.
If you have a straight edge about 18" or so, you can also double check the chainline by laying it edge-on against a chainring and carrying the line back to the cassette. You need to allow for the difference from where you measure, ie outside face of outer ring, to the centerline between both chainrings, which should line up with the center of the cassette.
I'm not sure a 5mm difference is enough to cause all your problems, since that corresponds roughly to one sprocket over on the cassette, but you might as well get things as close as you possibly can without spending money, then see how it goes.
Note that chainline calculations depend on the cassette width and axle width. Since you know your chainring centerline, check your cassette's, by measuring from the inside of the right dropout to the center for the cassette and subtracting that from 1/2 the axle width. ie. 130/2 -17mm = 43mm. The goal is to have both chainring and cassette chainline offset equal.
If you have a straight edge about 18" or so, you can also double check the chainline by laying it edge-on against a chainring and carrying the line back to the cassette. You need to allow for the difference from where you measure, ie outside face of outer ring, to the centerline between both chainrings, which should line up with the center of the cassette.
I'm not sure a 5mm difference is enough to cause all your problems, since that corresponds roughly to one sprocket over on the cassette, but you might as well get things as close as you possibly can without spending money, then see how it goes.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
Thread
Thread Starter
Forum
Replies
Last Post
mrrhtuner
Bicycle Mechanics
1
07-21-16 10:51 PM