Engine Breakin Period

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?
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Happy Trails wrote:

Bearing in mind that I have the mechanical aptitude of a turnip here are some links on engine break-in:
http://ask.cars.com/2007/10/engine-break-in.html
http://tinyurl.com/cb6upt
http://www.ntnoa.org/enginebreakin.htm
http://tinyurl.com/c55n4x
Try a Google search on "GM engine break in".
--
Civis Romanus Sum

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wrote:

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.
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wrote:

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.
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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 cam designs.
Important considerations include the areas of an engine that are lubed by "splash" and/or "oil mist".
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Ditto on what Ashton said ... good info ... IMO and all that rot
sumbuddie on da watchtower
On Sat, 4 Apr 2009 10:27:19 -0700, Ashton Crusher wrote

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