Interesting to note that the USA version has a different timing spec on the 603.970 than other markets: 14+/- .5 All .971 engines have the same 14*ATDC spec, and earlier versions all are timed at 15+/-1 ATDC.
(REF: FSM RA 07.1.1044-1100/3)

So, the timing was actually advanced 1* for the USA engine (and other engines starting 1989/1990) with the tolerance tightened up. Didn't seem to have any negative effect on the US market 602s, but I wonder why the timing advance was specified. Emissions likely.

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Gone to the dark side

- Jeff