[CR]Re: BB Length

(Example: Framebuilders:Jack Taylor)

Date: Mon, 13 Jan 2003 10:57:00 -0800 (PST)
From: "Bruce Schrader" <bcschrader@yahoo.com>
To: classicrendezvous@bikelist.org
In-Reply-To: <CATFOODko8C7wyfwjHN000003f6@catfood.nt.phred.org>
Subject: [CR]Re: BB Length

I run into this problem quite often while working on bicycles that have had either the crank or the bottom bracket spindle replaced in the past. I have several copies of Sutherland's Manual dating back to the early 70's and the most current one as well. But I find it's easier to take a few measurements and determine on my own what length and offset BB would be correct.

By "sighting" from behind the rear cluster up through the chainwheels, I can move my head left or right so that I'm viewing a straight line that the chainwheel will take and see which rear gear it lines up with. Ideally, in a triple crank/7sp cluster, the chain wheel that I sight on is the center one and the line it should take is through the center gear on the cluster (three on either side of the center one). If your eye sight is not that good, then a piece of string tied to a tooth on the front side of the chainwheel, running along side the chainwheel and back to the cluster will show where the chain line goes.

The problem is almost always that the spindle is too long. I take a measurement of the distance between the chain stays and the crank arm (at the pedal, both left and right side) and the distance between the inner chainwheel to the chain stay to see how far the crank will go in before anything starts hitting.

I can then do a simple subtraction to see what length spindle would be optimum and then get out the parts book and see what's available in that length or closest to that length.

I just changed a 121mm spindle with a 107mm this last week using this method and everything came out perfect and the shifting is nice a smooth and the chain is quiet on the extreme angles and the derailleur adjustments are well within their limits now.

One other thing to consider is the offset (if any) that's necessary on the chainwheel side to accomodate one, two or three chainwheels.

Now that I've written this simple explanation, it seems complicated to me.... but I still find it easier to determine (and more accurate sometimes) than spending much time in Southerland's manual trying to determine the correct length especially if I'm working with newer than Nuovo Record or Super Record stuff. I'm not that familiar with the different models of Campy that have emerged since then and those are the one's with the low "q" factor that require the shorter spindles. If it's Japanese or other European makes, then my methods work well also.

Good luck, Bruce Schrader San Francisco

____________________________________________________ From: GPVB1@cs.com Subject: Re: [CR]BB Length

One word Benjamin: Sutherland's Manual!

(OK, that's two actually...).

Greg "bookish" Parker Ann Arbor, MI USA ___________________________________________________

Date: Mon, 13 Jan 2003 12:23:25 +0200 From: Phil Grizic <pgrizic@haggie.co.za> To: classicrendezvous@bikelist.org Subject: [CR]BB Length

I hope that someone on the list can help me. I have quite a few bikes mostly with Campy equipment - Nuovo Record, Super Record, Grand Sport, Croce d'Aune, and various generations of Record. I seem to sometimes have a problem with the BB length and the chain line. Some of the bikes run very smoothly but some seem to object in the lower and the higher gears. As these bikes have been built up over the years with parts that I have managed to acquire - I think that maybe some of the BB's are not really the rights ones for the Cranks, either too long or too short. Does anyone have a chart of the recommended BB lengths matching with the various Campy Cranks? Or is there something else that I am doing wrong. Any suggestions will be welcome Thanks Phil Grizic Durban - South Africa

===== "Not all those that wander are lost." -J.R.R. Tolkien (1892-1973)

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