I was having a wonderful ride for myself, yesterday, on my Grubb, arranged, as-it-was, as a single-speed. It was a pretty flat ride on the M.U.P., but on the way back, there is one relatively long, gentle decline. I began pedaling faster, and suddenly, I could pedal no more. Something had caught, I thought. I slowed and looked down, to find my 3-arm, 40T steel (unbranded) chainring dramatically bent (folded, almost) between two of the chainring bolts.., bent out at least 2.., maybe 3 inches. Total collapse between the chain bolts.
My chainline was good. My chain tension was just right (not too-tight). I am not a particularly powerful rider, nor presently in remarkable shape. I was lucky to have been only 2M from home. It was a nice day, so my walk was not bad at all.
This strange occurrence has serendipitously given me some "wiggle" room concerning what kind of build I would find most satisfactory for the Grubb. I've decided to modernize the bb and crank, because I can't have this happening again. I found a good deal on a new cartridge bearing b.b., and a Stronglight Impact square-taper crank. It will obviously be much lighter than the Duprat? cottered one that is coming off today.
It must be that some (cheaper?) 3-arm rings are more prone to this kind of abrupt failure than their more-modern, 5-arm brethren.