Originally Posted by Sangetsu

I had the same problem with two Birdies which were not equipped with the original chain guards.

Installing a new crankset for the front is an easy job, but getting a front derailleur to work is easier said than done (and without the derailleur, the chain still hops off). I installed an Dura Ace 7800 crankset on my Birdy, it was a job that took only 30 minutes or so. But installing a derailleur was quite difficult. First I had to find an adapter, and of the three different adapters I tried, only one got the derailleur in the right position. Next, the swing arm pivot and the swing arm itself is so close to the chain rings on the crankset that the derailleur cage would come in contact. I remedied this by cutting away about one-third of the derailleur cage (some might be a little queasy about cutting up a brand new Dura Ace derailleur). The derailleur cage would now move enough to shift the chain from one ring to another, but when in the small ring, the derailleur lever came in contact with the right crank arm. I had to machine down the adapter to bring the derailleur closer to the seat tube.

I could have kept hunting for a better derailleur adapter, but having already tried three, I was getting tired of playing around with them. Another option would be to get a spacer for the right crank arm, and move it out a few millimeters to give more room.

But in the end, i got it working. It's nice to increase my gearing range, and I no longer have a problem with the chain falling off.

The aftermarket has a few chain keepers which will keep your chain from hopping off. You can also get a variety of chain rings with guards which keep the chain in place. And, finally, you can use an XTR derailleur which reduces chain slap when going over bumps.