Pedal Eyes and Re [CR]Broken Cranks..

(Example: Framebuilding)

Date: Sun, 08 Feb 2004 14:06:19 -0500
From: "HM & SS Sachs" <sachs@erols.com>
To: Norris.Lockley@btopenworld.com, classicrendezvous@bikelist.org
Subject: Pedal Eyes and Re [CR]Broken Cranks..


Norris Lockley wrote:

The reason that cranks break at the pedal-eye is, more often than not, = according to TA, because the shoulder of the pedal axle has been allowed = to cut into the surface of the crank thereby creating an "incipient = crack". It is to prevent this happening that TA always supplied thin = brass washers to place between the crank and the pedal. In recent years some manufacturers have beefed up this part of the = crank's surface by adding into the forging or casting a few extra = "thous" of an inch of metal. That might be an improvment but it does not = prevent the axle from actually chafing into the alloy of the crank.

Another reason that might cause the pedal eye to break is fitting a = "tight" pedal thread into a slightly "tighter" crank thread as sometimes = this can lead to tearing of the thread inside the crank. It is always = better in such circumstances to carefully tap out the threads, and = always use some form of lubricant when fitting the pedals. -----------------

Back in the 60s and 70s, I suspect another element entered the equation: In addition to the different It/Eng/Fr threadings, the actual length of the threaded part varied. Since steel is stronger than aluminum, pedals for steel cranks had shorter threaded portions (particularly, in my memory, French ones), and those for aluminum cranks had longer threaded shafts. The combination of a strong rider and short threading on an aluminum crank does not inspire confidence, although I have no documentation of frequency.

Your mileage may vary.

harvey sachs
mcLean va