I have a 21 speed mountain bike. I'm thinking of removing the large chainring in the front since I never use it and replacing it with a chain guard ring (if that is what you call it - it's just a plastic disk - something like this: http://www.amazon.com/gp/product/B00...pf_rd_i=507846 ).

I have no experience removing chainrings though. Is it realistic to do this myself? Could something like the product above simply replace the spot where the chainring is now? I realize that I will also have to set the limiter on the derailleur too - I'll have to figure that one out later.