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Hi All, I came across this post on Engine breaking-in(running-in) in an old forum - am pasting it verbatim as it gives a reason for it's actions.
Am biting my fingernails after reading it as I just took my Jul 26 delivery Swift for a long drive this weekend - anyway here goes -
Ben's guide to 4-stroke engine break-in:
The Practice. For the first 100 miles, only take short trips of <15
minutes. Do not rev above about 3500 rpm. Use full throttle in short
(2-3 second) bursts at low rpms (say 2500) - 5th gear on the freeway
is ideal for this. Do not do more than one full-throttle burst in the
same 2-minute period. Avoid driving for more than 2-3 minutes at the
same rpm - if you are on the freeway, vary your speed and alternate
between 5th and 4th gears.
>From 100-500 miles, increase the peak RPM you reach by 200 rpm each
time you drive the car (but don't go higher than redline). Do not rev
to your new peak under heavy throttle; instead, let the engine drift
up to the rpm under light load. For instance, pulling away from a
stoplight, leave the engine in first and accelerate lightly until you
reach the desired RPM, then shift. Continue the full-throttle-burst
procedure. Do not rev the engine high under full throttle, and do not
do either the peak-revving or the full-throttle procedure more often
than once a minute. Avoid driving for more than 5 minutes at any one
rpm - again, alternating between two adjacent gears and varying your
speed will work.
You will notice that each time you reach a new peak rpm, the engine
will be quite loud at that rpm, but after a few runs up it will quiet
down. This is a sign that the break-in is proceeding well. You will
want to have revved the engine to 6500(5500) rpm a few times by the
time you reach 500 miles. At that point I recommend you change the
oil, as most of the metal wear and contaminants from break-in are
released in the first 500 miles.
>From 500-3000 miles (the extended break-in) you can operate your
engine fairly normally. Most of the work is done. You should still
run the engine at higher RPMs on a regular basis (assuming you don't
in the normal course of driving ;-) ) and you should avoid prolonged
high-speed/high-stress operation, like racing or cruising at 110 mph.
I personally change the oil after 1500 miles since it will be dirtier
at that point that it would be after 3000 miles of post-break-in
operation, but it isn't critical. Be sure to change it at 3000 miles,
however. Although there is some difference of opinion on what KIND of
oil to use during break-in, the general consensus is to use normal
(non-synthetic) oil of the recommended weight (5- or 10-30).
>From 3000 miles onward, your engine is considered broken in. It will
probably continue to "loosen up" a bit over the next 3000-6000 miles,
so look for a small increase in gas mileage. Other than that, your
engine is now be ready for a long and productive life. Enjoy!
***** BEGIN TECHNICAL SECTION *****
The Theory. The primary goals of engine break-in are: 1) achieving a
good seal between the piston rings and cylinder walls, and 2) allowing
the engine to operate correctly throughout its RPM range. The major
enemy during the break-in period is localized heat buildup, mainly in
bearing surfaces (most notably the crankshaft bearings).
Initial state: When the engine is machined at the factory, many
wearing surfaces (places where parts rub against each other - cylinder
walls, bearings, etc) are purposely machined more roughly than they
could be. The reason for this is that it allows the engine to
complete the machining/polishing as it operates, thus allowing for the
individual variations inherent in any manufacturing process. This
wearing process, when complete, produces parts which will fit together
with very tight tolerances. However, the process also involves a
great deal of friction, which in turn means a great deal of heat. As
metal parts heat, they expand slightly. If the expansion goes beyond
a certain point, the parts will tend to bind with and/or score each
other. This must be avoided.
[To put this in plain english, the parts which rub against each other
are left a bit rough, and as the engine runs the parts will scrape
against each other until they wear down a bit and have a proper fit.
While they're still in the process of scraping, they can get very hot;
if they get too hot, they will damage each other in a permanent way.]
Since this sort of heat buildup is very localized, it will not show up
on the engine temperature gauge. Therefore, it is important to
operate the engine in such a way that the heat buildup will not reach
a dangerous level. More on this later.
Stress and Variation: Although the engine parts are metal and, as a
rule, quite rigid, they are still subject to slight deformation when
stress is applied. The largest stress in a piston engine is that
produced by reciprocating parts. The forces involved increase with
the square of the RPM. Any deformation will necessarily involve a
change in some tolerances inside the engine. Thus, in order for the
engine to operate properly over a range of RPMs, it is important that
it be exercised over this range during the break-in process so that
the wearing parts will experience the range of tolerances they will be
subjected to during normal (post-break-in) operation. Further, for
the wearing surfaces of reciprocating parts (most notably the piston
ring/ cylinder wall interface) operation at a single RPM for an
extended period of time will cause the machining process to progress
significantly further within the confines of the part's range of
travel without progressing at the point just outside that range, thus
building up a small ridge of metal just above the point of maximum
excursion.
[In order for your engine to run well from 1000 to redline, you need
to operate it at all those rpms while it is breaking in. If you
don't, the parts won't be used to working at the rpms you neglected,
and they won't work as well at those speeds]
Piston Ring Sealing: The seal between the piston ring and the cylinder
wall is crucial to getting good economy and performance from the
engine. A bad seal will allow more blow-by, reducing the amount of
power the engine can produce with each power stroke and thus reducing
both its horsepower and fuel economy, as well as allowing combustion
gasses to get into the crankcase and contaminate the oil AND allowing
oil to get into the combustion chamber and be burned, producing the
characteristic blue-smoke-from-the-tailpipe syndrome (note that oil
can also get into the combustion chamber via the valve stem guides,
but that's not something we can do much about during break-in). The
key to getting a good piston ring seal is high combustion chamber
pressures. Embarrassingly, I don't know why (can someone fill me
in?). High combustion chamber pressure is produced under hard
acceleration; also, the lower the RPM the longer that pressure is
maintained during each power stroke. SO - to get a good piston ring
seal, hard acceleration at low RPMs will give the best results.
Since hard acceleration also produces more heat and more stress
(leading to friction and still MORE heat), it should only be used in
brief bursts, followed by a couple of minutes of "normal" low-stress
operation to allow the heated parts to cool down.
Localized Heat Buildup:
As previously mentioned, wearing parts will produce inordinate
amounts of heat as they polish each other. This produces local points
of intense heat inside the engine, with temperatures far higher than
the engine as a whole (which shows up on the temperature gauge) or
even of the surrounding parts. The most susceptable points in an
engine for this kind of heat buildup are the crankshaft bearings,
which must withstand enormous stress and pressure. If the bearings
are allowed to get too hot, they will expand to the point of scoring
each other or (*gulp*) binding, producing a spun bearing. During the
initial stages of engine break-in, there is no satisfactory way of
keeping these bearings cool during even mild engine operation except
to turn the engine off after every 10-15 minutes of operation and
allow the bearings to cool down.
The theory I have outlined about should now be sufficient to explain
the "practice" section of the break-in instructions. For the first
100 miles, keep the rpms low and the trips short to minimize the
stresses and heat buildup in the bearings, and use short full-throttle
bursts to seal the piston rings. From 100-500 miles, gradually
increase the RPMs to allow the wearing surfaces to correctly mate, and
continue using full-throttle bursts to ensure ring sealing. Use
cooling periods (the 1-minute rule) to minimize the heat buildup
produced by the high RPM operation and the full throttle bursts. At
500 miles, change the oil to flush out all the metal particles
produced by the wearing process.
Hope this helps all of you new car owners!
- Vinay | 
1st August 2005, 16:24
