There is a massive difference between making one engine that will run for a few hours and making thousands of engines all of which will operate under all foreseen conditions for hundreds of hours. Napier didn't have the knowledge of metallurgy or production engineering let alone the equipment, the fault is as much with those awarding the contract as those bidding.I agree totally.
According to LJK Setright, Napier had been "living hand to mouth for years" and a lot of the Sabre's problems were due to the fact that the production models could not compare to the hand built prototypes. Apparently their factory in London was full of antique lathes etc.