Fordiesel69 271 #1 Posted May 8, 2013 I made a big mistake and ordered the wrong pulley. What I pulled off of my C-121 was a 4" and I ordered a 5-1/4" by mistake. I know this will increase ground speed, but will I also be requierd to get another belt or mod the guard? C-121 K301 12HP engine Share this post Link to post Share on other sites
gwest_ca-(File Mod) 11,509 #2 Posted May 8, 2013 8-speed or automatic? Larger on the transmission will slow it down. Not paying attention Larger on the engine will speed it up. Sounds like you have the 8-speed but what shaft diameter? The Toro Master Parts Viewer is the cause of many mistakes. Garry Share this post Link to post Share on other sites
Martin 2,133 #3 Posted May 8, 2013 i did this mod on my c125 8 speed. went from 4 to 5 1/4, you will have to get a hydro belt and as long as the belt guard on the c121 is the same deal as c125, i.e. used for both 8 speed and hydro, it will work with your existing belt guard...... heres how i did mine...... Share this post Link to post Share on other sites
brandonozz 168 #4 Posted May 9, 2013 I'm on the other side of the fence. I have been thinking about slowing down my C-120 so my 1st gear in low range is a bit slower. I find when using the tiller for breaking ground I have to use the clutch all the time. Not to hijack this thread but any recommendations on pulley size (and which one to change to give the best fit) to slow it down a bit? Ozz Share this post Link to post Share on other sites