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Cleaning Cylinder Heads and Blocks

Cleaning is just as much a part of engine rebuilding as disassembly, machining and reassembly. Cylinder heads and engine blocks (as well as all the other engine parts) have to be cleaned down to bare metal so the castings can be inspected for cracks, wear and other defects.

By Larry Carley

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The cleaning process should remove all of the dirt, grease, oil, rust, scale and carbon deposits that have accumulated over the years. With painted castings, the old paint also has to be stripped away so the surface can be repainted. Even if you’re working with brand new castings, a final cleaning is still necessary after you’ve completed your cutting, resurfacing and honing procedures to remove residual traces of oil, metal chips and honing residue.

Dirt, oil and grease are all soluble to some extent depending on the cleaning solution or chemicals that are used. Chemical solvents are very effective cleaning agents, but their use has been restricted in many areas by rules that limit the release of Volatile Organic Compounds (VOCs) into the atmosphere. Aqueous cleaning solutions that contain detergents or alkalines have replaced many solvents, and typically require a certain amount of heat (130 to 170 degrees F) and agitation to clean effectively.

Hard carbon deposits in the combustion chambers and exhaust ports are probably the most difficult contaminants to remove. Chemical solvents can soften and remove carbon deposits, but they can’t be used universally. If a solvent cannot be used, some type of media blasting may be necessary to dislodge heavy carbon deposits. Combining the scrubbing action of ultrasonics with water-based cleaners can also provide an effective means of removing hard carbon deposits.