A rebuild is one person's work on one afternoon. Its quality depends on who did it, what was on the shelf that week, and how carefully anything was measured. Some are excellent. Plenty are not, and you find out in month four, on a motorway.
Most of what is sold as a rebuilt engine is a gamble on a stranger's care, sold with a warranty that covers the part and not the labour bill you pay twice.
Remanufacturing to production standard answers that objection directly:
Block restored → every other component new → assembled on a line → tested.
It happens on a production line. The same sequence, the same tolerances, the same checks, on every unit. Not a judgement call.
The block is restored. Every other component is new. Not "whatever looked worn", and not a mix of whatever was on the shelf that week. One casting is measured, machined and brought back to specification. Everything that bolts to it, turns inside it or seals against it is a new part.
The finished engine is tested under the conditions used for new engines. The same test regime, applied to confirm it meets the original design specification.
It carries our 12-month commercial guarantee, because a controlled process is something you can stand behind. A workshop rebuild rarely comes with terms this clear, and when it does, read what they exclude.