We painted a IH 140 tractor many years ago and used gray primer--BIG MISTAKE. We had removed several pcs for cleaning and mechanical repairs prior to painting. Used rattle can gray for primer. It was very hard to get all the primer covered with the tractor assembled. If we weren't real careful we would get drips and runs. I had to specifically paint thin coats on those pcs, which was hard since you couldn't really get the gun close enough to target those areas. I was especially glad when the last gun of paint went on that machine. Seems we were constantly going over it with a drop-light looking for areas that didn't cover.
