Is this vintage fork safe to ride?
 

I have been enjoying learning about and taking apart my dad's ~1973 Gitane Super Corsa since I got it a few weeks ago. However, I noticed yesterday upon removing the fork that a crack has propagated within the flattened section of the threaded portion of the steer tube. I have no idea how long it has been there. It seems to me that threaded steer tubes would be subject to less stress than their threadless counterparts, but I still would like some feedback regarding the sanity behind riding this fork. I am not planning on making this bike my daily commuter, but I would like to ride it regularly. Would it be wise to find a replacement fork before I ride this bike? Thanks for your input.

Don't risk your life. The crack will only propagate slowly until there isn't enough metal to hold. The stem would probably retain the fork but pieces of cracked metal could jam your steering or something.

I wouldn't allow anybody that I cared about to ride on that.

good candidate for a "steering column transplant"...you could even have a standard ISO thread column stuck on and never have to worry about FR headsets or stems again. Bernie Mikkelsen in Alameda, CA is currently doing that job for $80.

Turn it into a wheel truing station.

+1 Great chance to have a frame builder do a transplant.