Classification depends on how the goods are presented at entry. A diesel engine imported separately from the alternator is classified as an engine under SITC 71382. A complete generator set — engine and alternator assembled or imported together as a functional unit — is typically classified under the generator set heading. Importers should review the condition of the goods at time of importation and consult a licensed customs broker when the assembly status is ambiguous.

Off-road compression-ignition engines must meet EPA Tier emissions standards under 40 CFR Part 1039, with the applicable Tier level determined by the engine's rated power output. An EPA Declaration Form must be filed at entry, and the engine must carry a valid certificate of conformity. Engines that do not meet current Tier standards may qualify for limited exemptions (e.g., replacement engines for older equipment) but require specific EPA authorization.