Originally Posted by
thefultonhow
I just replaced my old three-speed crankset with a 42-tooth largest chainring (don't know the other ones, and I never used them) with a single-speed crankset with a 50-tooth chainring. I also replaced the cassette on the rear with a new one for two reasons -- one, the 7th gear (smallest chainring) on the old one was worn and so the chain was skipping, and two, I wanted a larger ratio spread with lower gearing on the first couple of gears due to the larger chainring up front. I tried seventh gear once, in rush-hour traffic, but I missed shifting down when I had to brake suddenly, and when I tried to accelerate and put pressure on the drivetrain in order to do so, the chain fell off the rear chainring. When I hadn't been loading it up, it had pedaled fine and with no skipping. I also had replaced the chain at the same time, so I had basically a completely new drivetrain that should have meshed fine.
I was wondering if it's possible to block the chain from coming off. Can I put any kind of guard in the way that will prevent the chain from moving any farther outboard? (In the current setup, it can fall onto the spindle that attaches the wheel to the frame.) Are there any other methods? TIA.
Your semantics appear to be off.
If you are referring to the rear sprockets as the place the chain came off, you probably need adjust the limit stops on you rear derailleur.
If the chain is coming off the front chainring, you probably have too much chainline angle from the rear sprocket to the chainring. That would be likely scenario. Another possibility is the front derailleur is in the wrong position and you may need adjust it to the right -particularly if you have a friction shifter up front-you could do it with the shifter.
You could but an idler in between the sprocket and chainring to keep the chain on the chainring, but it would rob you of power. Also, the front derailluer could be used to hold it onto the chainring-but that friction also robs you of power. Another option might be to go back to a triple front (or even a double would give you a better chainline).