Standto;
I remember reading an article about motorbike parts once. The cost of the bike if bought in component form and assembled accordingly, was about ten times that if bought brand new from the showroom.
There is justification for some of this price difference. I am assuming that the following is applicable to all automotive manufacturers. The values given are approximate.
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GM in Australia would shut down a component production line (say camshafts) every few months. All of the machines would be refurbished so that the production tolerances could be brought to 0.0001". The first 2,000 new camshafts would be assigned to 'replacement parts'. The remaining 50,000 camshafts produced would then go to the engine assembly line. The camshafts going to the assembly line would have lower tolerances, of course.
This was done for two reasons. One, they wanted to be sure that replacement parts worked, and two, the cost of refurbishing all of the component production line every 2,000 parts would significantly increase the price of a new car.
I assume that the helicopter industry requires a tolerance of 0.0001 on
all parts produced.