Can anyone explain exactly why driving at a constant rpm for "too
long" can harm an engine during a breakin period. No manufacturer
ever specifies how long a period is acceptable and what is too long a
period at constant rpm. Why is that?
I've read arm-chair experts opinions about wear patterns and
blah-blah-blah, but no one ever explains exactly what happens that
could be damaging to engine parts.
Who knows for sure?
Bearing in mind that I have the mechanical aptitude of a turnip here are
some links on engine break-in:
Try a Google search on "GM engine break in".
From what I learned the problem with just a constant rpm, like a long
trip, is that you don't load the rings enough to get them to seat well
against the cylinder walls. The rings are held against the cyl walls
by not on the tension in the rings that is pushing them out, but also
the combustion gas pressure goes behind the rings and adds additional
outward pressure on them. When you just loaf along cruising down the
road it's not much load and not much combustion pressure compared to
accelerating so the rings don't get pushed hard against the cyl wall.
While it would seem like you would not want to push them hard against
it to avoid wear, you need that initial "wear" to seat them. All that
said, modern cars are machined to better surface tolerances and
surface finish and supposedly it's not nearly as important now to
worry about "break in" as it was years ago. Nevertheless, following
the typical old school break in practice can't hurt anything and might
help. I suspect it would be still be a good idea on a one-off rebuild
if you want maximum life. Also, you don't want high rpm's right way
on a cam till it's broken in (don't want them too low either for the
first few hours from what I've heard). My routine on a new engine is
to keep drive normally but no "fast" starts from stop lights and no
operation over 3500 rpm for the first 1000 miles and vary the speed as
much as possible (no long cruising). So on teh free way you might
slowly yo-yo the speed from 55 to 75 when possible so you get some
coasting and some acceleration.
Cam breaskin is lo less than 2200 RMP for 6 to 8 minutes.
New engine or cam replacement
Accelleration seats the rings with combustion pressure, hard decell
draws oil up around the rings due to high vacuum with throttle closed
(over-running). The combination helps seat new rings.
Almost a non-issue on today's production engines, but still good to
know with a rebuild.
Yes for the piston rings...
Cam/lifter break in isn't such a concern with modern Ford engines. Cam
followers have been "antifriction" design for quite some time making
localize loads less of a concern over the older "not quite so" flat tappet
Important considerations include the areas of an engine that are lubed by
"splash" and/or "oil mist".
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