FYI, this is from 6speedonline.
"This is from a post to another list originally made 9/16/1999. I have
been using this procedure for many years (at least 18 years). I both
agree and disagree with the link you posted. I'll explain why after
you see my procedure.
I have a standard break in procedure that I use, it takes about an
hour if you are diligent, and when you are done, break in is complete.
The biggest point of grief with a new engine is the unrelieved
stresses in the pistons. You want to heat and cool them in a
predictable way with an incrementally increasing thermal load. I
usually start at 20% throttle and go in 10 or 15% increments until I
get full throttle. Bursts should be 15 to 30 seconds, followed by 5
minutes part throttle cruise to let the pistons cool and resize
themselves. You can figure out that 30 seconds in top gear at full
throttle will have you going pretty fast down the road, so you need a
clear stretch to do this, but I have never had a problem with leak
down or bad piston fit using this technique. That crap about "XXX"
miles is just so the average driver doesn't blow things up.
Also, I assemble the cylinders dry, but turn the engine over for about
15 seconds with no fuel or ignition before my initial start up, then I
run it up to about 25% of redline as soon as it catches for 30 seconds
or so. Once I have my initial 30 seconds and no gushing leaks, I take
it out for a drive right away. I want to put pressure on the rings and
valves to get them to seat well and that can't be done without a load,
so off we go down the road for about 5 minutes, then return to the
shop to check for oil or coolant leaks. If all is OK, back out on the
road for final break in.
OK, that's what I have recommended. I disagree with Motoman because he
is ignoring the whole issue of grain structure in the pistons. If you
are using used pistons, then there is no need for any kind of loading
tactics like these, just a few full throttle runs at soon as the oil
is up to temperature to seat the rings and you are done. Cast pistons
have not aligned their grain structure after casting, and forged
pistons have unrelieved stresses from the forging process. Both
require heating and cooling cycles to allow the grains the opportunity
to align themselves under thermal load. It isn't possible to do this
in the manufacturing process because pistons are not heated evenly in
service. This process is no different than heat cycling your tires, a
well known science among racers. I completely agree with Motoman's
assessment of the manufacturer's recommendations. They are crap. I
also completely agree with getting a load on the engine as soon as you
can. I didn't notice any admonishments about allowing a new engine to
idle, but I NEVER allow a fresh engine to idle, it is the kiss of
death IMO.
Ken, in your situation, you have little or no control over how the
engine was initially fired, and BMW being reasonably intelligent and
diligent have already used an initial firing procedure designed to
seat the valves and rings quickly. Just take it out and drive it, put
a load on it, and be happy with it.
Lance Wolrab
