There are many studies showing that the performance results for engines operating with biofuels are acceptable, although very few long-term analysis of wear and maintenance problems are shown. Three mono-cylinder compression ignition engines were tested for approximately 1000 h each, with pure diesel oil (0100), pure soy methyl ester (SME100) and pure castor oil methyl ester (CME100). The lubricating oil analysis didn't reveal any excessive amount of metals compared to the engine with pure diesel. Viscosity decreased very soon to values below the minimum recommended due to dilution with the methyl esters, especially with SME100. The injection system analysis showed that opening pressures, hydraulic flux and corrosion levels were acceptable. The SME piston showed a very small crack. A higher amount of carbon deposits and gum formation was found over biofuel pistons, indicating poor combustion. Piston ring seating and gap were inside specification. Cylinder liners presented no damage on running surface. The valves presented abrasive and adhesive wear, contact fatigue for SME100 and marks at valve seating for CME100, considered acceptable after 1000 h of test. The results obtained show that the use of pure methyl esters fuels was acceptable for these engines regarding wear and maintenance problems. (C) 2010 Elsevier Ltd. All rights reserved.