As I learned from going through this process, painting an engine block (and doing a good job) is no easy feat. The reason for this, as you’ve likely already heard, is that getting a good quality result requires a lot of preparation. From my experience, there are two main things that make preparation difficult. First, used gasoline engines are especially dirty, and you want your nice paint to stick to the raw metal and not whatever contamination is on the surface of the engine. Second, you have to be careful about what you paint because paint can probably cause premature engine failure if it gets in certain places. For example, clogging fluid passages with paint, or getting paint in areas where it could break off and clog fluid passages could easily lead to premature failure.
To deal with the issue of dirt and surface contaminants, I first used engine degreaser and scrubbed everything well. Before this, the block also went through a hot tanking process while at the machine shop to help clean it up. Degreasing removed a lot of the remaining oil on the engine, but there was still a decent amount of rust and oxidation. As such, I used various metal brushes as well as a rotary tool to carefully brush off most of the stuff that I could reach. Afterwards, I degreased the engine again and also used some acetone to wipe down the surface and ensure it was contaminant free before painting.
To control which surfaces got painted, I was very meticulous about applying multiple layers of painter’s tape. Because my block was also freshly machined, I felt that I had to be extra careful. I imagine if you were sending the block to get machined after painting then you wouldn’t have to worry as much about getting paint on certain surfaces because the machining will remove it.
To apply tape to the block, I used a technique that I read about somewhere online. I applied multiple layers of painter’s tape ensuring that I not only completely covered each surface that I wanted to tape but also applied tape extending beyond the edge of each surface. Then, I used a hobby knife to cut the excess tape off the edges of each surface. It took a while to develop a technique for being consistent and accurate, but once I had a technique it actually wasn’t that hard. The technique I developed involved following the edge of the surface with the knife blade while holding the blade at an angle and using a slight sawing motion. When the knife was sharp, I found it would easily glide through the tape and allow me to trace the surface edges. Once you make the cut, then you simply peel off the excess tape.
To paint the engine, I used an automotive high-temperature enamel paint. Once I knew the surface was nice and clean, I started by applying a few coats of primer. The primer is supposed to help the paint stick to the engine while also filling in pits in the surface, which will allow you to achieve a smoother finish.
The primer was surprisingly easy to apply. It didn’t take very much primer to get what looked like an even and effective coating. This was in contrast to the red paint, which was much thinner and required many more coats and cans of paint. Nevertheless, once the primer dried I starting painting the engine red. Following the paint instructions, I applied additional coats within an hour of the previous coat.
After all of this, the engine sat around for a couple weeks drying. I didn’t originally intend to leave the engine sitting for so long, but other stuff came up and, frankly, it was nice to take a break after doing all of this tedious work. Eventually, I came back to the engine and removed all the tape. I think it looks really good! Although, to be honest, now that I’m writing this after the engine has been installed into the car, painting the block probably wasn’t necessary. The valve cover is really the only thing that’s readily visible. Oh well.