Bent Chain Ring
 

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.

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Wonder if it could have been somewhat out of alignment and pedaling loads caused the condition to worsen until there was collapse.

Sounds quite odd in my experience. Will look forward to reading the observations of others...

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Never heard of that before. Are there any pictures?

Oh yeah.., I forgot to mention that the spider got bent, too, so that's why I had to throw it out. I didn't get any photos of the chainring, but it was folded somewhat neatly in half along that 3-4" section. Alignment could have had something to do with it, I suppose. It happened when I started to pedal harder.
The crank was never 100% straight. I had only ridden about fifty miles on it. Upon closer inspection, it seemed that the metal of the chainrings was kind of soft.
Well.., on to something better.

Like the one Justice Scalia took perhaps?

Alternately, there is always an "Osterman."

The Osterman Weekend (1983) - IMDb

Is there any evidence of the spider starting to separate from the crank? If so, this is why you want a single piece crank-spider instead of a spider swaged onto the crank.

No.., no.., no scali bread (I am cutting down on carbs). Well, maybe with a nice chunk of gouda and a drizzle of.., anyway, this will reveal the secret to my enigmatic signature:


Thanks for the recommendation: I'll put Osterman Weekend on my IMDB Watch List.

[MENTION=160128]1989Pre[/MENTION], please forgive me, but my failure to understand reaches the level of mistrust. What crank is this? Is the ring swaged to the crank arm? Is the ring bolted to the spider? If the latter, was a bolt missing or loose? Has the crank been through a bad fire?
Did you get a piece of rebar stuck in the crank?
Whatever went wrong, it's a new one to me. Need photos. Need more info. Need... Yes, please forgive me, need to be convinced.

I'm disappointed that there were no pictures of gore to accompany the story. ;)

Folks in SS/FG report folding a chainring now and then, but it usually comes out that the chainline wasn't very straight, a bolt went missing, or the chain was loose and jammed as it came off. As it is, we have precious little info to go from.

Gremlins

Therm, what do you mean by "gore"?
You're probably right about some measure of mis-alignment or a jamming of the chain. I went through the links of the chain once I got it off, and they all seemed fine. I think the chain jumped the teeth on the chainwheel and got caught and pulled the un-supported section down. The fact that it is a 3-arm crank probably weighs-in, as-well. I do not own a camera, and have little intent to purchase one. If you have any questions, ask.

I was mostly teasing. ;) Glad you weren't injured when it happened.

I do have a morbid fascination with bike parts that have failed, and David Keppel's pardo.net site is like crack for people with this affliction: http://pardo.net/bike/pic/