How to Paint an Engine Block

You want your engine to shine when you pop the hood, don't you? For most hot-rodders, the engine is the whole point of building, driving, racing, or otherwise owning a kick-ass machine. But it's not as simple as picking up a rattle can from the corner parts store and setting off a spray bomb in your mama's driveway. The news here is both good and bad: Unlike painting your car's sheet metal, an engine paintjob is way easier, can easily be done at home, and involves very few cash expenditures, but as with a full-vehicle paintjob, you really need to sweat the details bigtime. Cut the corners and you won't like the look, and you may discover bigger problems down the line.

We're in the midst of building a 1,000-plus-horsepower 392ci Chrysler third-generation Hemi, but the techniques we used to paint our engine block can be used on any aluminum or iron cylinder block, whether it's a Mopar, Ford, or Chevy V-8. Heck, even a six- or a four-cylinder engine won't shy away from a good coat of paint! We chose to paint our Hemi after the short-block was built but before the rest of the engine was assembled; this stage is the ideal time to paint a block because it's a ton easier to mask off for painting, and the paintjob won't get beat up from the assembly process. Obviously, you wouldn't want to paint your block before it's cleaned, inspected, or machined, but if you want your aluminum parts to be painted for a stealthy effect (intake manifold, cylinder heads, water pump) you might want to wait until assembly is farther along. We didn't want our aluminum parts painted, so the short-block stage worked best for us.

If you want your engine to look great for years to come, it needs to be prepped properly before a drop of paint hits it. This can go two ways: roll the dice with an unknown block, inspect it as best you can, then clean and paint it yourself; or take it to a machine shop to have it professionally inspected and cleaned. The more power you want to make, the more effort and money you'll need to invest up-front, with procedures like hot-tank cleaning, sonic checking the cylinder wall thickness (vintage blocks should have at least .120-inch), and magnafluxing for cracks. With hot-tanking, you'll have the choice of a hot bath with a mild detergent (shown above), or one with caustic soda. If you plan to reuse your cam bearings like we did, go with a hot tank cleaning that uses a mild non-sudsing detergent.

Once you get your block back from hot-tanking, put it on a good engine stand and plan on going over the entire surface again. Any caked-on dirt left in crevices (it tends to collect around gussets and pan rails) will only look amplified after you paint over it. You can pick up a spray can of non-chlorinated parts cleaner or brake cleaner at the same time you buy your engine primer and paint (we found a can of Summit-branded parts cleaner here for $4.99). Our engine is going together at IMM Engines of Indio, California, and here IMM's Johnny Wadlund is shown cleaning the 392ci Hemi BGE block with some parts cleaner around the edges of the pan rail.

People are always searching for ways to cut corners and the question always gets asked: Can you paint an engine without removing it from the car? That's a negatory, big fella. You'll never be able to mask off the areas that don't need paint, and this photo only begins to show how much stuff is still attached to a modern fuel-injected engine after it's been removed from the car. You can't paint a fully dressed engine out of the car, much less while it's still between the fenders in an engine bay. If the engine is partially disassembled—or, more correctly, partially assembled—you'll achieve your best results without the risk of having to redo any of your work.

Our spidey-senses tell us you've made the decision to paint your engine and you want to know how many cans of paint you'll need. Before we get to that, we'll reiterate that you need paint specifically for engines and other high-temperature things like exhaust manifolds. To summarize Dupli-Color's description of their spray-can engine enamel: It contains ceramic resins for maximum heat dissipation and gloss retention, and for protection from exposure to excessive heat and automotive fluids. Dupli-Color Engine Enamel is designed for racing, street-rod, and vehicle-restoration enthusiasts, resists temperatures up to 500 degrees F intermittently, and produces a superior finish that won't blister, flake, crack, or peel. We've painted bunches of engines with it at HOT ROD, and unless your engine block powers an ocean-going yacht, you'll only need one can of primer and one can of color coat.

For this 392ci Hemi build, we bought one can of Dupli-Color Primer (DE1612) and two cans of Chrysler Hemi (DE1652) at a total of $41.97, but we only used one can of color coat (laying down two coats) so we could've spent only $27.98 on paint supplies. Beyond that, we secured a can of non-chlorinated parts cleaner (Summit, SUM-941241) at $4.99, a roll of green 3M "frog" masking tape (TES-7000048805) at $11.99, a pack of disposable utility-knife blades (WMR-W744) at $1.99, and got our engine builder IMM Engines of Indio, California, to inspect then hot tank our block with a mild soap solution for another $100. Altogether, we spent a total of $146.95 to paint this 392ci Hemi, but if you'd rather have Brian Hafliger (above) at IMM paint your engine block as part of an engine-building program he gets $200 for the job—a good deal considering the roughly three hours of labor involved in prepping, masking, and painting the block.

Like we said up front, the devil is in the details. There are a lot of precision-machined surfaces on engine blocks that need to be protected from paint and overspray—these are sealing surfaces for gaskets, fastener holes, motor mounts, and other sensitive areas that can't see paint. Cover all of these areas with 2-inch-wide green masking tape. (Most gearheads call this tape "frog" tape because of its generic green color, but note that Frogtape is a brand of green tape known for its clean edge lines that is used for the same purpose.) Make sure that the surfaces are clean and dry for maximum adhesion. It is not necessary to completely cover cylinder bores, the open crankcase, bellhousing flange, and timing-chain access area since you'll be painting the block with a masking board made of a random square of cardboard—just make sure there's ample tape coverage at the edges to be painted.

Of all the operations involved with painting an engine block, it's the masking trim-job that takes the longest time and makes the biggest difference in the cosmetic and functional outcome. Here the idea is to carefully trim away excess masking tape along the edges of the block, using the razor's edge to scrape rather than using the point to cut. Green "frog" tape is well-adapted to this operation and produces sharp edges that seal the block effectively against paint seepage into the covered area. When used in this fashion the razor blade is a consumable item, so you'll need to start with a box of these. (A set of five blades from Summit costs $1.99 but they can be found virtually everywhere.) In our accompanying video you'll see that trimming the paint mask is fairly involved.

The 392ci Hemi block, like many late-model fuel-injected V-8 engines, has a lot going on in terms of machined areas that need masking; besides the pan rail and timing cover sealing surface seen here, you can see another 17 additional machined areas within view that needed masking. If in doubt that a machined surface, dowel, or attachment hole needs masking, just do it.

If you've done everything right, doing the actual painting will be the fun part, starting with the primer coat. Don't skip straight to the color coat because primer is designed to aid the adhesion of the paint, improve the paint's durability, and give the color coat an even color brightness. It's also another layer of protection against harsh chemicals. You'll need a thick, straight-edged piece of rectangular cardboard the length of your engine that can be used as a handheld mask to keep paint droplets away from the cylinder bores, pistons, crankshaft, rods, timing chain, and other paint-averse areas. Shake the spray-can vigorously and hold it 12 to 18 inches from the surface. Dispense paint only while moving the can gradually over the surface, being careful not to let the spray stop or dwell over any area too long. You don't want to get this far only to create ugly drips and runs.

After an hour's dry time for the primer coat—about the time it takes to eat lunch—you can apply the first color coat. (Dupli-Color recommends painting in temperatures between 60 and 95 degrees F, and around 70 percent relative humidity.) Here is where you get to let your freak flag fly; you may choose to go with the color associated with your particular engine's brand loyalty (in our case Dupli-Color Chrysler Hemi Orange), or you may want to step out on the wild side. Before choosing to paint your engine block the same color as your car, research whether there is a vendor that makes custom colors in a high-temperature formula. (Dupli-Color offers 34 colors in its engine enamel lineup that you can check out here.) A second color coat is highly recommended, and there is a one-hour recoat window, after which you must let the paint fully cure (one week) before laying down another coat.

For color-conscious hot-rodders who pay attention to such things, Chrysler Orange and Chrysler Hemi Orange are not the same; Chrysler Orange is slightly darker and less vibrant (more pastel) than Chrysler Hemi Orange, which is the most vibrant of all the Dupli-Color orange engine paints available over the counter. Chevy Orange by contrast is whiter (also more pastel) and is visibly redder in hue than either of the Chrysler Oranges. To complicate things, there are two shades of Chevy Orange, Chevy Orange and Chevy Orange-Red, the latter of which is quite nearly a tomato-red. Always test your color on a piece of cardboard first to see if it's the right shade and whether you've shaken the can enough!

Removing the masking tape after the final color coat is one great feeling! The trick is to do this while the paint is still a bit tacky; waiting until the paint is dry can cause cracks in the color coat at the edge where the tape is pulled off. Dry time is only an hour, after which you'll be good to complete your engine assembly.