Vintage French cotter pin problem

[swee'pea99]

It just will not stop working loose. And every time it does I have to drive it a bit further in. To the point where now the head has disappeared into the crank and the nut on the other side won't hold it, even with the new added washer. Wah!

 

[swee'pea99]

Don't suppose there's anything to be learned from the failed pin?...

 

[Deleted member 26715]

That is not the correct sized pin

 

[midlife]

The French had 2 sizes of cotter pin, in the 70's anyway. Maybe you have the "thinner" French cotter pin. Or it's not French?

 

[tyred]

Is the crank a tight fit on the spindle? In that photo it looks like l see space but maybe I'm imagining it.

The crank can stress and deform if it was used with a loose pin for years.

Are both sides the same?

 

[midlife]

Ah, see what you mean, the crank should be a snug fit on the spindle.

 

[silva]

A thick washer to make it not bend, but it should be a larger surface / diameter too, in order to spread the pressure over the alu of the crank. And considering the directions of the forces exerted, a rectangular shape with the long side front/back, a thick plate with a hole drilled in it, would give the forces more support surface in their directions.
It's abit a flawed design. The benefit that square taper is for crank mount, is here the drawback.

 

[swee'pea99]

A little postscript to this little tale...

After yet another pin effectively disappeared through the crank, I admitted to my daughter that I was out of ideas, and the only thing I could think of would be to ask at the bike shop over the hill that opened a couple of years back, see if they had any idea/other cotter pins/other.

Well, she just got back and...."He took one look at it and said it's the crank that's worn, which is why the pin won't hold it. But he said he had one round here somewhere, and he took the old one off and put the new one on, and fixed it proper tight. And he wouldn't take a penny." She's delighted, as you can imagine! The benefits of actually knowing stuff, eh?

I do like a story with a happy ending.