i would open it up see what happened to it but a clunking noise probably not good and yes you can go to a bigger one if you want to just get the numbers off the old one and ask for a direct replacement just make sure of the shaft length and diameter i just replaces the 19.5 horse B&S on my parents John Deere cause the rod broke and i went to a 21 horse bolted right on pluged right in and was cutting grass in 45 mins to a hour it came complete all i had to do was put it on add oil and go