Cold Case - Chain falls off largest ring
Hi. I don’t have this bike anymore. I don’t know how appropriate it is posting an old problem here but I virtually lost a bike over it. It is a 20+ year old mystery that I would like an answer to and I thought this forum might help me out. I had a mountain bike that the chain used to inexplicably fall off the outside of the big chain ring. I took it to three different bike shops and they could not solve my problem. I replaced the chain after the second shop of the bike shop visits and this did not solve the problem. I presume that because the problem occurred while I was peddling, not on or just after a gear change, that the de-railers were properly aligned. The bike had bio-pace chain-rings (yes, it was that long ago). Only one bike shop offered any solution, which was possible bent teeth on the chain-ring. It used to get a stiff link after it came off the cog that no amount of ‘wiggling’ the links could fix properly; either that or I did not have the ‘guts’ to wiggle the stiff link any further. Eventually, the rear de-railer broke a pin (maybe known as a pivot) that joined it together after it ‘slapped’ itself to death from the stiff links going though it. I was a bit younger then and did not know much about bikes, so I traded the bike in on a new one. In my current knowledge and personality I may have tried to change the big-ring (large chain ring that the chain kept falling off on the outside) on it to see if that helped, however, like I said, I did not know much about bikes and no-one offered that solution to me. Like a car with bad mechanics (and you’re not a mechanical person) I got rid of it because it was turning into a ‘money bucket’ of problems.
What do you think caused the chain to fall off the big ring?
As a post script: I was in the Navy at the time and personalities are such in that organisation that I would not rule out sabotage – maybe that will help with an answer.
If you’re young you probably want to know what Bio-pace chain-rings are: they were elliptical chain-rings brought out by Shimano that were designed to smooth-out your peddling stroke. For some reason they did not survive as an idea and Shimano reverted back to round chain-rings. As an addition to the above I used to ride with someone who had Bio-pace chain-rings and the chain did whip to a small degree because of them.