Onetrack:
However, the problem remains with high-volume production tooling, whereby wear on tooling has to be very carefully scrutinised, or tolerances commence to go out of spec. When this happens on large-scale production, all engines suffer from tolerance problems.
I was under the impression the high cost of the aircraft engine is related to total dis-assembly, and hand re-assembly... with blueprinting and modification of the engine, the main aim, to meet the more rigorous requirements of aircraft useage. Component balancing to much tighter levels than automotive requirements is high on the list... as is checking of all components for meeting precise specifications. Few people realise how many automotive engines are often assembled with components that barely meet specifications.
I was told a story about Holden engine assembly, many years ago... and have never been able to determine the story as true, or urban legend. I wouldn't be surprised if it was true.
The story goes that the Holden engine assembly line had a bloke checking component specs, and colour-marking them accordingly.
This gent doing the specification measuring was reputed to have had three colored chalks. Green, yellow, and red.
Green-chalked components fell into the ideal levels of meeting specifications. These components went into Export engines. Yellow-chalked components just met specifications. These components went into local production, private-sale vehicles. Red-chalked components were outside specifications, but could be passed with a shove. These components were installed in company fleet, and Govt-order vehicles...
True or not? I don't know... but one things for sure... if we actually saw what happened when our beloved automotive motors were assembled in the factories, we would quite likely be appalled...
1. Production tooling doesn't "wear" like that any more. Furthermore statistical quality control has been in place for at least Forty years in Japan and any out of tolerance condition will be picked up by trend monitoring long before it causes problems.
The problems with the engines may well be due to environmental factors or design issues, such as coping with Australias hot summers. Be aware that most Japanese cars have an infinite number of variations to suit local markets, right down to the level of dust sealing applied. It could easily be that the engine concerned did not have a cooling system that could cope, or the torque curve of the engine was not matched to the gearbox and vehicle weight. You put a free revving engine in a situation where it can't rev and guess what happens?
2. Regarding the colour marking of parts on the Holden assembly line, what was seen was most probably correct, however the interpretation was most probably wrong. Where extra tight tolerances are required, for example con rod bearings and mains, we often use
selective assembly.
While each component is within tolerance (say + or - 1 ), we measure each one individually and grade it within say three bands eg; Nominal -1, Nominal, Nominal +1. - mark them with your red white and blue chalks.
Measure the mating components the same way and mark them accordingly. By matching our components that both have tolerance bands of + or - 1, we can reduce the spread of tolerance on assembled units from 4 units to 2 units.
Of course if your process doesn't put out equal spreads between bands, you can end up with some head scratching engineering guesstimates to make.
My summer job one year was to sort out all this stuff for Medical gas fittings at the old CIG.