The basics of reconditioning an engine
The basic steps of reconditioning an engine start with obtaining a good core unit to work with to begin with.
Once good core unit is obtained it needs to be cleaned and inspected. After initial inspection the units get broken down into their component parts for a thorough diagnosis. The cylinder head(s) is removed the connecting rod /piston assemblies are removed, the crankshaft is removed and all individual components are sent to their respective inspection stations to have them blueprinted to spec.
The engine block is stripped bare and sent for machining, cylinder bores are checked for roundness and machined if needed. In some cases the cylinder bores are machined and sleeves are inserted to bring the engine back to original standard sized bores. The block is then flipped over and the mainline journals for the crank are machined to make sure everything is perfectly lined up and within specifications for the reinsertion of the crankshaft once machining is complete.
The cylinder head station initially skims the surface of the cylinder head to ensure there is a flat mating surface and then it is fitted to the pressure testing machine which will identify if the cylinder head has any internal cracks. Once these initial steps are completed the cylinder head is broken down and valves are removed to inspect the valve seats. As long as everything looks as it should, new valve stem seals are installed, valves are reinserted into the seats and lapped into place to create a positive seal and the head is built back up.
Over on the crankshaft station the crankshaft is mounted on a specialty horizontal milling lathe where the cranks are checked for straightness. If machining is needed to bring the main and big end journals to a specific tolerance, it is done now. After machining the crank is then polished on the journals to a high quality finish needed to mate it with the replacement crank bearing sets.
Connecting rods are removed from the pistons and inspected for both cracks and straightness, if a connecting rod is found to be either cracked or bent, it is discarded and replaced with another one that has previously passed these tests. New small end connecting rod bearings are fitted at this time. The piston are cleaned individually and the old ring sets removed. The ring landings are cleared and cleaned to accept the new set of piston rings and then they are reassembled with the connecting rods and sent over to the reassembly station.
When all individual units are completed in their specific reconditioning stations all of the parts then meet up again at this reassembly station so the unit can be built up. Using new quality gasket sets and oil seals the units are reassembled, paying close attention to manufacturers torque specs and sequences. Once the unit is reassembled it then goes for final quality control where the technicians confirm both compression and oil pressure readings and ready the units for delivery.
In a nutshell this is the basic process adhered to for many different reconditioning firms, some add a few more steps here and there but all in all it is the same process to get to the same final result giving you an engine with all internal wearable parts being replaced with new and machine work done to the entire unit to make sure it can have a long and dependable life once fitted into a vehicle.