Chain Rub on the Front Derailleur, Finding the Problem on my Vintage Gitane Bike

My Gitane road bike had some chain rubbing on the front derailleur, caused by lateral movement on every turn of the crank. Finding the problem wasn’t straightforward.
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[@steelcrazy409]

pretty interesting.I've got a similar problem with a Gitane that has a Suntour crankset on it 53/42 on a modern sealed BB,not bent but the smaller chainring passes very close to the chainstay which looks to have a very short relief bent into it for chainring clearance.Toying with the idea of replacing the 42 with a 40 or 39 in order to get a bit more clearance.