Abstract The manuscript discusses the issue of diagnostic informativeness of measurement signals recorded during electronic indication of marine engine cylinders. It was noted that the “ fault-syndrome” relations of the diagnostic model determined on this basis are usually ambiguous, which forces the need to search for additional symptoms that ultimately confirm the diagnosis. A method of multi-symptom recognition of disturbances in the engine’s working process is presented by means of measurement experiments carried out on a real object and numerical experiments, with the appropriate usage of its “digital twin”. In the first part of the manuscript, the possibilities of carrying out diagnostic conclusions about the technical health of the valve timing system of a single-cylinder, naturally aspirated Farymann Diesel type D10 marine engine were examined based on simultaneous measurements of its standard operating parameters, exhaust gas composition, in-cylinder pressure and acoustic vibrations generated from the cylinder head by the working fuel injector and cylinder valves. Selected metrological issues of conductiong such measurements. As a result of the engine tests, extensive wear of the camshaft cams was identified, which resulted in premature closing of the exhaust valve and delayed opening of the intake valve. The shifts in the valve timing were so significant that there was practically no valves openning overlap in the cylinder flushing phase. To finally verify the primary formulated diagnosis, dynamic measurements of the engine valve timing were conducted using external inductive sensors, and then the camshaft was dismantled from the engine and subjected to direct optical examinations..