Combines F2 main drive belt

If you mean the belt from the motor to the cross shaft not a bad or time consuming job. You have to take the traction belt off first. If variabale speed your op manual will tell you to either have it in slow or fast speed setting, then remove the hydraulic line and the lower belt. The top belt should have an idler to loosen and maybe a bracket or two. I haven't had to do this for ten or so years.

run vs to fast. Shut off machine. Find a deep well socket or other such item to wedge in between now spread apart lower sheaves and will allow sheave to turn. Back off main drive idler and or pull up and block so no tension and possibley now remove belt from engine pto. Now loosen main shaft hose and pull out on vs sheave on main shaft or pry out. Oil will squirt out of fitting. The main drive belt can be rolled under vs belt wiht a bit of difficulty as is now loose as a goose. New belt can be rolled in and reverse the process . IF you cant get belt in undewr vs belt unscrew main shaft sheave and remove.