Re: [CR] stronglight 49d crank bottom bracket bearing size?

(Example: Component Manufacturers:Campagnolo)

Date: Mon, 14 Dec 2009 05:16:52 -0800
From: "verktyg" <verktyg@aol.com>
To: David Snyder <dddd@pacbell.net>, <Classicrendezvous@bikelist.org>
References: <81CB9178E8D1431BAEBA8211E74E2394@BenjaminPC> <0F5372C6B12E4B4A821A759DFDC6958D@ddddPC>
In-Reply-To: <0F5372C6B12E4B4A821A759DFDC6958D@ddddPC>
Subject: Re: [CR] stronglight 49d crank bottom bracket bearing size?


About 45 years ago I took a short engineering course on bearings. I seem to remember that around 1948, maybe 1949 inch dimensions were made the world standard for precision ball and roller bearings (as opposed to the style of bearings found on most bikes).

Metric bearings are made for special high precision applications but I don't know if the actual balls are metric or inch sizes.

I've never heard of metric sized balls being used on bikes.

As others have mentioned, the standard for most classic bike BBs is 11 1/4" ball.

You can frequently find bearing retainers or "cages" with nine 1/4" balls used in BBs. Campy retainers for 1/4" balls held 11 balls.

Retainers are supposed to have the advantage of keeping the balls separate to reduce friction and wear. Also 9 balls might have slightly less friction than 11 balls. But... in my opinion, the main reason for using bearing retainers in BBs and headsets is for ease of assembly.

Bottom brackets are constantly exposed to changing forces while pedaling. Even the most supple riders continuously load and unload the bearings side to side plus BB bearings are subjected to both axial and radial forces.

For this reason I recommend using 11 loose 1/4" balls to more evenly distribute the forces. There's going to be a slight space between them but they will be continuously moving around as you pedal.

I'm sorry to offend by my sense of component vanity does not extend to Campagnolo loose balls! ;-) Campy probably buys balls and has them packaged to sell for an exorbitant amount of money. I doubt that they are any better than standard Grade 25 balls, the best grade commercially available.

http://americandad.biz/ts/gradechart.htm

Buy grade 25 chrome steel balls. Grade 25 specifies the sphericity of the balls. These are round to 0.000025" ±0.000025" with a diameter tolerance of ±00.0001". Chrome steel is a special alloy designed for use in bearings.

You can get them at many bike shops but make sure that they are grade 25 chrome steel not the cheaper carbon steel balls that many LBS use. You can also buy them online for a reasonable price or from this eBay seller: <http://tinyurl.com/ycet5mv>.

David Snyder brings up a good point about mating parts. Most Stronglight BB spindles have the name stamped into them. Early Stronglight cups have a fairly distinctive look, later ones have the name stamped into them too.

Did you inspect the cups and spindle before reassembly? The bearing surfaces should be smooth with no wear or chips. Most worn out BB parts that I've seen have signs of flaking rather than plain wear. See this web page for examples of bearing failure. The first description shows flaking.

http://www.emersonbearing.com/technical-toolbox.html

Most cheap and some better quality BB parts are only case hardened rather than through hardened. The hard surface layer may only be as little as 0.005" deep. Also cheap case hardened parts are usually made from low quality 1018 carbon steel instead of a higher quality alloy steel.

BB parts tend to wear on one side of the bearing surfaces due to the pedaling forces. If you used worn out parts they will be almost impossible to properly adjust and will probably be noisy too.

Chas. Colerich Oakland, CA USA

David Snyder wrote:
> That's very interesting.
> I have heard of at least one reference to the use of 6mm (.236") balls
> in Stronglight bb's, and if so that might allow one add'l ball???
>
> How many of the 1/4" balls fit now? IIR there should be 11, and I've
> taken apart a few factory builds.
> Also, iir, The late Sheldon's site made note of a rolling diameter (ball
> track diameter) discrepancy with respect to using non-Stronglight cups
> or spindles with mating Stronglight parts. This might explain clearance
> differences regardless of ball size.
>
> Anyone have details on this?
>
> Sorry, I don't have a loose Stronglight bb here to look at.
>
> David Snyder
> Auburn, CA usa
>
> ----- Original Message ----- From: "Benjamin I Cole"
>> Are 1/4" bearings correct for the early 70s stronglight 49d crank
>> bottom brackets? With 1/4", there is a gap but not enough for 1 more
>> bearing. This seems to be causing the bb to be noisy. Is this the
>> nature of these? Sorry, i don't work on much french. I checked
>> archives and sheldon but didn't see anything.