[alfa] Re: break-in

["Jim Steck" <4sfed@xxxxxxxxx>]

Dear Digesti,

At the risk of over-simplifying, I'll define break-in as the process of
wearing off the high spots on parts that rub together . . . to the point
that the oil film is thicker than the height of the surface asperities.  The
risk of running too fast, too hard, too soon is that the micro spots will
rub, overheat and weld together.  They break apart immediately, but leave an
even rougher surface.

With modern bearings and finishing techniques, main and rod bearings do not
need any break-in . . . except at startup, the bearings and crank are smooth
enough that they do not touch.  They do require warm-up before being run
hard.  The only way break-in can affect rod bearings is if a ring or a
piston scuffs a cylinder, and the extra friction overloads the bearings.

Rings and cylinder walls, cams and tappets, and to some extent, new oil pump
gears need to be broken in, but after 20 minutes of moderate load and RPM,
the break-in is 90% complete.  Short bursts of high load shorten the time
required to complete the process.  On a new car, the hardened gears in the
transmission and rear axle take much longer to 'mate' and are the main
reason the OEM's recommend an extended break-in period.

-- -- --
Jim Steck, AutoComponenti
8906 Darke County Line
Brookville, OH 45309
ph: (937) 884-5142
fax: (937) 884-5144
email: jim@domain.elided
web: www.autocomponenti.com


> ------------------------- original message ------------------------
> Say what you want, but I'm considerably more concerned about glazing
> the rings during this unfortunately necessary period than I am about
> spinning bearings when revving a fairly fresh engine.


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