Spray Paint Engine
Applying a few coats of paint to your rebuilt engine provides protection as well as good looks. Here's some tips to spray paint engine block and parts from an aerosol spray can.
Prepare The Surface
The key to every good paint job is in the preparation. To get paint to stick to a cast-iron engine block or cylinder head, the metal must be clean and dry. Cast-iron is porous, kind of like a sponge. It soaks up oil, and when something is painted that has oil in it, the paint may eventually peel off because the paint itself cannot soak into the cast-iron so it can grip or adhere to it. Clean the surface with mineral spirits or brake parts cleaner. Use painters quality tape to mask off anything you don't want painted.
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Generally, spray paint fumes aren't as harmful as other paint, but good ventilation provides you not only with fresh air, it also helps the finished product dry faster. Select an area that is well-ventilated.
Most likely the engine block will be on a stand, but for painting engine parts, place them on a piece of cardboard or cover the area with paper. You can prop up the items to be painted with pieces of wood or cinder blocks. Try to keep your work piece off the ground where dirt and dust settle.
When To Prime Metal Before Painting
If you're spray painting something for the outdoors, you want to protect against moisture and rust. A metal paint primer is needed here. If the metal is not primed, water can seep in and oxidation will start.
Some metals, like aluminium, aren't easily painted and require a metal paint primer. The surface is not adhesive enough and the paint may flake off. A primer will provide a good base-coat to help the paint adhere correctly.
If you decide a metal primer is necessary, you have a choice between a rust paint primer or a galvanized metal paint primer. A rust primer is best for stabilizing and minimizing rust and making the rust easier to paint over. A galvanized metal paint primer is best for painting aluminum-like metals.
If you are priming the metal surface with spray-on primer, allow it to dry for at least one hour before spraying the top coat. Thicker applications dry slower than thinner coats.
Shake Spray Can Thoroughly
Shake the paint can vigorously to mix the paint. Turn it from top to bottom in your hand for at least one full minute. You will hear the mixer ball rattle in the can. Repeat the mixing process throughout the painting process.
Test Before Painting
Always test the spray paint on scrap material or a piece of cardboard before aiming it at your metal project. There are two important reasons for this. First, it's a check to make sure the nozzle is clear. I've sprayed a few brand-new cans (after shaking well) and had paint dribble out on my hand. The quick fix for this is to take a spray nozzle off an old can that worked well.
Another reason why you should test the spray can before you spray paint the engine is to get used to how the paint flows. As you do a little "test painting" on something other than your project, you'll get a feel to how close you can get before getting sags and runs. Try holding the can as close as 6 inches from the surface, then back away if the paint starts running.
Spraying The Color Coat
There's several ways to spray paint, the most common being starting at the top and slowly sweeping downward from left to right with slight overlap. Hold the can approximately 10 to 12 inches away from the metal surface. Getting too close causes drips and runs, and painting too far causes brittle, uneven spraying.
You can pause after each sweeping motion by letting go of the trigger. Once the first coat is done, allow the paint to dry for 30 to 60 seconds. Continue to apply a 2nd light coat, then stop and observe the surface. Sometimes two coats is all that's needed.
Spray Paint Engine Parts
The oil pan seen in the following pictures was sanded down to bare metal, scuffed, then painted GM "corporate" blue (no primer needed).
Allow Paint To Dry
When you are satisfied with the appearance. stop and allow paint to dry. Allow the last coat of paint to dry before handling the object. Don't rush the drying process, let it sit at least overnight to be sure.
Sanding Out Imperfections
If you see dirt or grit in the paint, first allow the paint to thoroughly dry (one day minimum). Then, take a small 600 or 1000 grit strip of wet/dry sandpaper (folded over) to lightly smooth out the imperfections. Keep the surface area wet, and sand lightly to avoid cutting through the color coat.
When Not To Paint
Avoid windy conditions. Humidity greatly affects how paint dries and adheres. Choose locations and times of day accordingly. Spray painting metal in between 50 to 80 degrees is optimum.
Where To Buy Spray Paint
Most of the time, I'll stop at a favorite auto parts store, but you can also find spray paint at home improvement and hardware stores. Be sure you buy a brand of spray paint that was intended for metal surfaces. I've had good results with Duplicolor, Plastikote, Krylon, and Valspar. These are only four of many top-name brands.
Proper Spray Paint Can Disposal
Don't toss empty spray paint cans into your garbage can. Even if it's empty, they contain paint residue and are considered toxic waste. Make a habit of disposing spray cans properly.