Joined: Jan 2010
Posts: 9,835
Likes: 1,816
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
It takes me 5,000 miles to wear a chain that far.
Cross-chaining couldn't cause such rapid chain wear, but at some point can derail a chain.
If this is "industrial" chain, it won't be appropriate for bicycles, but a $12 KMC "Z" derailer chain always lasts a couple of thousand miles or more on a road bike.
3/32" over 12" is worn out to the point that rapid sprocket wear will follow.
What conditions is the bike ridden in? Swamps?
I have to agree that the bb is appropriate if the little ring now has only 1 or 2mm of clearance with the frame.