[CR]Gear case clearance cranks for 1950's double chainsets


Example: History:Norris Lockley

From: "neil foddering" <neilfoddering@hotmail.com>
To: classicrendezvous@bikelist.org
Date: Fri, 14 Oct 2005 10:09:43 +0000
Subject: [CR]Gear case clearance cranks for 1950's double chainsets

I'm in the process of my first restoration of an early 1950's racing machine (an Ephgrave Number 1) whcih I acquired as a frameset. I believe it dates to 1954.

It was originally fitted with Campagnolo Gran Sport front and rear mechs, which were too far gone to use, and has the appropriate brazed-on cable stops. It also has Campagnolo "open C" rear dropouts.

My questions arise from my attempts to find a suitable double chainset. I've consulted old cycling handbooks and catalogues, and come across the term "gear case clearance", often shortened to GCC. In regard to bottom bracket axles, I understand that it originally referred to a slightly longer bottom bracket axle, to allow clearance for a chaincase between the inside of the crank arm and the bottom bracket. I also understand that, when double chainsets became more widely used, gear case clearance axles were stipulated to allow for the inner chainring.

If this is incorrect, then I'm happy to be set straight.

I've also come across a couple of references to GCC cranks. The most detailed reference was in a 1950 Fonteyn catalogue, in reference to Simplex double chainwheels, and I quote:

"Durax Cranks (For Double Chain-wheels)

Although the Simplex chain-wheels have a normal three-arm fixing, it is necessary to fit them on a right-hand crank which has the extra clearance away from the chain-stay, to allow clearance for the front derailleur to operate. An ordinary gear-case clearance crank will do, but we strongly recommend using the Durax cranks for double chain-wheels, the right hand of which has the exact clearance required.

Note - gear-case-clearance cranks need to be fitted on a gear-case clearance bottom bracket axle."

A mid-50's Ron Kitching "Everythin Cycling" catalogue refers to cranks in N.G.C.C. (Non Gear Case Clearance), G.C.C and Semi-G.C.C.

I shall possibly be using 46/49 Gnutti chainwheels.

My questions are:

1. Did all makers use GCC clearance cranks for doubles, or did some achieve the clearance some other way, (e.g., by simply using a longer axle with double rings attached to the same cranks as used for their single chainsets)?

2. Is it possible to identify which maker did what?

3. How do I identify GCC cranks, as opposed to non-GCC ones? (Short of buying a load, that is, and comparing them!).

4. What pitfalls are there in mixing and matching chainrings by one maker to cranks by another, assuming, of course, that the BCD and the crank bolt hole diameters are the same?

5. Is there a correct way of selecting axle width? I've noticed that double axles come in various widths.

Thanks!

Neil Foddering
Weymouth, England