I think you meant impact wrench, but yeah I'm in the same boat. I just picked this one up:
DEWALT DCF899P1 20V MAX XR Brushless High Torque 1/2" Impact Wrench Kit with Detent Anvil - - Amazon.com
I have a nice Ingersoll Rand pnuematic 231C with 600 ft/lbs impact wrench that wouldn't budge it. I'm probably just not getting enough air to it though as this impact should be able to do the job. This electric cordless one I just picked up has a lot more torque (Heavy-duty impact mechanism with max torque 700 ft./lbs., breakaway torque 1,200 ft./lbs). I actually haven't tried it on a front sprocket yet but I think (hope) it will do the trick.
DEWALT DCF899P1 20V MAX XR Brushless High Torque 1/2" Impact Wrench Kit with Detent Anvil - - Amazon.com

I have a nice Ingersoll Rand pnuematic 231C with 600 ft/lbs impact wrench that wouldn't budge it. I'm probably just not getting enough air to it though as this impact should be able to do the job. This electric cordless one I just picked up has a lot more torque (Heavy-duty impact mechanism with max torque 700 ft./lbs., breakaway torque 1,200 ft./lbs). I actually haven't tried it on a front sprocket yet but I think (hope) it will do the trick.