New Engine Break-In:
One of the most asked questions is how do I break in
my new motor? The short answer is that no break-in is
necessary. The only thing that is necessary is to seat
the rings. All clearances and fitments should be perfect
after blueprinting and precision assembly. So how many
miles do you have to drive it to seat the rings? The
cylinders are round, the rings are round, the bore is
freshly honed and therefore your engine should be ready
for tuning immediately. They will continue to seat better
over a short period of time but you should be ready
to go tune right away.
Do I need to drive it 500 miles before I tune it? Absolutely
not. How about 50 miles? No. Perhaps the best thing
to do is to drive it all the way to your trailer and
tow it to a competent tuner. In second position on the
things NOT to do list is trying to break
in an un-tuned engine by driving it. Too lean an air/fuel
will begin to heat and distort parts, too rich will
wash the oil off the cylinders causing premature wear.
What is in first place on the things NOT to do
list? Boost on an un-tuned motor. Within 2 to
3 seconds the pistons and cylinders can be ruined.
Well I did put in a new base map or Im just running
off the stock Honda computer. Cant I drive it
like that for a few miles? Im not even boosting.
Well what is the base map? Just someones idea
of what numbers will start your car. Just an educated
guess by someone who does not have a clue what components
you are running in your set-up. Its not intended
to drive on for any extended period of time. The same
with that stock Honda computer. It could be ok but it
could also be dangerously wrong.
So what exactly do I do at the first engine start-up?
Pull the spark plugs and crank the motor with your starter
for a maximum of 30 seconds or until you see the oil
pressure gauge begin to register. Re-install the plugs
and wires and fire up that candle. While keeping one
eye on the oil pressure gauge, use your other eye to
scan for fuel leaks. If there are no fuel leaks, look
under the motor for any major oil or coolant leaks.
If that is ok, run the engine for 5 to 10 minutes while
keeping an eye on the temperature and pressure gauges.
Keep the rpms between 1000-3000. Shut the engine
down and double-check everything. You are now ready
But my engine was already tuned from my previous set-up.
Well, what happened to your previous set-up? Did you
melt a stock piston or crack a cylinder? No problem
because now you have forged pistons and sleeves? Wrong.
Although you now have stronger components that will
take more abuse, you are still not right on your air
fuel mixture. Get that thing tuned properly ASAP.
OK, I did it my way instead of yours and now Im
burning a lot of oil. What happened? Well basically
you scarred up the skirt of the piston, messed up the
surface of the cylinder wall and maybe even egg shaped
the cylinder. New pistons are tapered smaller on the
top to larger at the bottom of the skirt. Your piston
to wall clearance is measured at the bottom of the skirt.
As the engine warms up to operating temperature, the
upper portion of the piston begins to expand slightly.
The bottom of the skirt does not expand much. When you
boost in a lean condition, the upper part of the piston
expands quickly. Since the ring land area is cut smaller
than the tapered skirt below it, the first part of the
piston that pushes into the cylinder wall is just below
the oil ring. Thus you will see the worst scarring on
your piston right under the ring lands where the excess
heat is the highest
The more heat that is generated, the harder the piston
pushes into the cylinder wall. The uninformed would
blame the piston damage on bad piston to wall clearance.
Untrue. If that were the problem, the damage would show
up at the very bottom of the skirt. What has happened
is that you have expanded your piston to the point that
it has just ground itself into the cylinder wall. Keep
expanding the piston by super heating it and it will
push your cylinder egg shaped and maybe even balloon
out the cylinder slightly. At the same time this is
happening, your ring lands will begin to distort to
where they will never seal properly again. Sometimes
after doing this, the engine will still run but it will
be a smoker. This all happens in a few seconds of high
boost with a lean air fuel ratio. Also it can happen
from 500 freeway miles of driving where the tune up
is off enough to build excess heat at a slower rate,
thus doing the same damage over a longer period of time
the end results are the same. Death to your pistons
and cylinder walls.
OK, Im just going to turn the fuel pressure way
up and run extra fat, that way I wont hurt anything.
If you run too rich, you will wash out the
rings. First, excess fuel will run down the cylinders
taking the lubricating oil with it. This promotes direct
metal-to-metal contact between the rings and the cylinder
wall. This contact does several things. The upper ring
begins to wear quickly. The middle ring is actually
designed as a tapered oil scraper (it is not used for
compression control at all) and the taper will begin
to wear down to where it becomes flat rather than angled.
When that happens, it can no longer control oil away
from the combustion chamber. The last thing that happens
is that pretty cross hatch design begins to wear off
of the cylinder wall. While most people think that the
cross hatch is there to help seat the rings, it also
has a secondary purpose. That is to hold microscopic
amounts of oil in the grooves to help lubricate ring
to cylinder walls. With the walls smooth and no oil
control help from the middle ring and a tired upper
ring, oil will begin to mix with fuel in the combustion
chamber. When this happens, your 93 octane fuel probably
hits a value of about 80. Then detonation comes into
play and begins to beat holes in the pistons, among
So whom can I blame for this mess? The blind machinist
that honed my piston to wall clearance? That poor quality
Brand X piston manufacturer? The idiot pro engine builder
that assembled my block? My ex-friend that helped me
put this all together? Those ignorant engineers that
gave me a bad base map with my engine management system?
The guy on the internet message board whose buddy knows
that it takes at least 1000 miles of break in before
you can tune an engine properly? All of the above? Probably
none of the above. Go look in a mirror and ask
started this engine and had no idea what the air fuel
ratio was? Who just wanted to jump on it one time to
see if it would haul? Who didnt know that their
injectors were at 100% duty cycle at 4000 rpm but they
wanted to see how it would run at 6000 rpm? Why it was
you. Get that thing tuned right away. You will notice
that the more you drive a tuned motor, the stronger
it will feel. This is just the rings seating in their
final 5-10% as they thank you for tuning first.