Originally Posted by
mawn
its a triple "Shimano SG A-52-42-30", the previous owner removed the 30.
next thing to do is price a 30t small ring of the correct bolt pattern, price a left side triple shifter that matches the one on your bike, and price a front derailleur that is made to do a triple shift if the one on the bike is not a "triple".. the part number for the Front derailleur is on the back of the chain cage... post that part number here, or look it up on the internet, to see if it's a "triple"....
once all the costs and availability is figured out, then you can make the correct decision for your riding needs...
The Crank swap will be the easiest, and best choice for lowest price total, eh?
the "triple" install will have other hidden costs too... possibly shift cable, cable housing, bar tape(depending on Shifters used), and possibly a rear derailleur...
installing a hollowtech II crank is easy.. remove pedals, remove old crank and bottom bracket, CLEAN everything, put a dab of grease on the BB threads, install Bb, slide new crank in place, side new Left crank arm on, tighten clamp screws, adjust chain length and front derailluer,.. then go ride!