Dieselhead wrote:
At AMG, they may specify the exact sizes from the parts suppliers,
(.001mm) or they have the parts picker matching pistons to bore
ahead of time. Modern machining allows all cyl to be the same
within .001mm and the same for pistons. Process control (SPC) and
better machines make this possible. It is the main reason why
american engines routinely go 300k miles , not 40k to 120k as in
the 60s.
I thought it was partly due to better oil but mainly due to the
demise of carburetors and chokes, eliminating wash down of the
cylinder walls and reducing dilution of the oil.
Were the first TBI small block Chevy engines (which routinely went
200k+) that much different from the 1950s versions?
OTOH, the first car I ever took to 200k had a non feedback
carburetor, I drove it for quite some time with a dead choke
pull-off solenoid, and it never saw a drop of synthetic oil. The
engine was heavily worn by the time I drove it to the junkyard, but
it still went over 1000 miles on a quart of oil.
It was a very early 1980 (assembled in the spring of 1979) Chevy
Citation with the 2.5 liter Iron Duke from the Pontiac Astre. The
original owner worked in Detroit and lived in Lansing, so it had
145k mostly highway miles when I bought it in 1985.
Mitch.
Fuel INj may have some part in the improvement, but it mostly is due
to the new automated machining centers. Where most tolerances were +
or - .005" and Pistons etc+ or - .001, now production tolerances can
be .001 and pistons etc can be .0005 or less.
Metallurgy and other factors contribute too. The mid 60s GM 6 cyl
had such bad cast iron they would be too worn at 40k to 60 k miles to
be able to bore them and rebuild. A true throw away engine.
But the order of magnitude more precise machining along with the
tools of quality (re-imported from Japan) made the long life of our
OM60x engines possible. The OM61x engines long life came from
craftsmen carefully selecting and fitting variable pieces together.
with today's possible manufacturing tolerances, it is not out of the
question to grab a block, grab 8 pistons out of a box and have a
perfect fit on the crank and all 8 bores.
Reliability and repeatability of measurement, and of manufacturing is the key.
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