The Definition needed is to REMANUFACTURE:
A Re-manufactured Engine is one that is fully re-machined to the Manufacturers Original Engine Specifications and had all of the consumable components renewed!
This can be further explained by simply viewing the BS AU257 standard on the British Standards site. The 12 month guarantee applicable, demonstrating the confidence of work.
It is the only standard that the AA and RAC, The RHA, MoD, Dept. of Transport approve!
Engines appear to go wrong for many reasons; But usually its because of a previous problem with one of the 3 x liquids ! The Oil, Water or Fuel.
The lack of the first two:- OIL & WATER will give you sudden, extreme and expensive failures,
while any irregularity in fuelling, can give you, excess smoke, poor performance and cause premature wear with eventual failure!