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View Full Version : what oil to use for engine run-in???



David
01-15-2001, 06:31 PM
A recent argument raged on another list as to what oil should be used during engine brake-in, well my feelings are as follows :

The key to run in is the finish of the cylinder bores. Modern machining
> > technique now achieves what is called "plateau" honing.
> > The bores should be as close to perfectly round and perfectly straight
as
> > possible within economic reasons.
> > The microsurface reflects two different types of friction on it, from
the
> > rings and from the pistons and the way the oil forms a lubricating film.
> > The pistons press against the side of a cylinder because of the
geometry
> of
> > the connecting rod and the crankshaft throw. During the power stroke,
the
> > connecting rod pushes the crank shaft in one direction but pushes the
> piston
> > with equal force in the opposite direction, with the center of piston
> force
> > at the level as the piston pin.
> > These forces vary on the walls during compression, part throttle, or
> other
> > high vacuum periods. So the piston varies in both the levels of force
and
> > the direction of force upon the walls.
> > The rings work in quite another way. Gas pressure from the combustion
not
> > only pushes the piston down, but the ring as well, through the gap
between
> > the piston and cylinder wall. The ring presses down against the
descending
> > piston and also gets behind the ring and forces it against the cylinder
> > wall.
> > "Seating" the rings means much less for the rings and MUCH more for the
> cyl
> > wall surface. It is the initial frictional wear of the engine block
during
> > the run in period that we should be concerned with.
> > Plateau honing can achieve this finish virtually eliminating the need
for
> > both run-in and ring seating. Final honing should be of a grit of at
least
> > 280.
> > In a perfect world the surface should retain just enough crankcase oil
> > thrown up by the spinning crankshaft journals to keep the minimum amount
> on
> > the surface for ring lubrication for one cycle up and down.
> > Lastly and most important is the final hot soapy water cleaning before
> > reassembly.
> > Any grit left behind will stay on the rings indefinitely and cause
> premature
> > wear.
> > The choice of oil is, well, what ever you want.....
> > Dave@Taos Garage Annex in Albuquerque
> >

> >

Basil
02-10-2001, 08:43 PM
Well, I think I would use as close to what the original manufacturer recommended

Basil