What's The Best Way To Break-In A New Engine ?
The Short Answer: Run it Hard !
Nowadays, the piston ring seal is really what the break in process is all
about. Contrary to popular belief, piston rings don't seal the combustion
pressure by spring tension. Ring tension is necessary only to "scrape" the
oil to prevent it from entering the combustion chamber.
If you think about it, the ring exerts maybe 5-10 lbs of spring tension
against the cylinder wall ...
How can such a small amount of spring tension seal against thousands of
PSI (Pounds Per Square Inch) of combustion pressure ?
Of course it can't.
How Do Rings Seal Against Tremendous Combustion Pressure ?
From the actual gas pressure itself ! It passes over the top of the
ring, and gets behind it to force it outward against the cylinder wall.
The problem is that new rings are far from perfect and they must be worn
in quite a bit in order to completely seal all the way around the bore. If
the gas pressure is strong enough during the engine's first miles of
operation (open that throttle !), then the entire ring will wear into
the cylinder surface, to seal the combustion pressure as well as possible.
The Problem With "Easy Break In" ...
The honed crosshatch pattern in the cylinder bore acts like a file to
allow the rings to wear. The rings quickly wear down the "peaks" of this
roughness, regardless of how hard the engine is run.
There's a very small window of opportunity to get the rings to seal really
well ... the first 20 miles !
If the rings aren't forced against the walls soon enough, they'll use up
the roughness before they fully seat. Once that happens there is no
solution but to re hone the cylinders, install new rings and start over
Fortunately, most new bike owners can't resist the urge to "open it
up" once or twice,
which is why more engines don't have this problem !
An additional factor that you may not have realized, is that the person at
the dealership who set up your bike probably blasted your brand new bike
pretty hard on the "test run". So, without realizing it, that adrenaline
crazed set - up mechanic actually did you a huge favor !
Here's How To Do It:
There are 2 ways you can break in an engine:
1) on a dyno
2) on the street
On a Dyno:
Warm the engine up completely !!
Then, using 4th gear:
Do Three 1/2 Throttle dyno runs from
40% - 60% of your engine's max rpm
Let it Cool Down For About 15 Minutes
Do Three 3/4 Throttle dyno runs from
40% - 80% of your engine's max rpm
Let it Cool Down For About 15 Minutes
Do Three Full Throttle dyno runs from
30% - 100% of your engine's max rpm
Let it Cool Down For About 15 Minutes
Go For It !! Frequently asked Question:
What's a dyno ?
A dyno is a machine in which the bike is strapped on and power is measured.
It can also be used to break in an engine.
NOTE: If you use a dyno with a brake, it's critical during break-in that
you allow the engine to decelerate fully on it's own. (Don't use the dyno
brake.) The engine vacuum created during closed throttle deceleration
sucks the excess oil and metal off the cylinder walls.
The point of this is to remove the very small (micro) particles of ring
and cylinder material which are part of the normal wear during this
process. During deceleration, the particles suspended in the oil blow out
the exhaust, rather than accumulating in the ring grooves between
the piston and rings. This keeps the rings from wearing too much.
You'll notice that at first the engine "smokes" on decel, this is normal,
as the rings haven't sealed yet. When you're doing it right, you'll notice
that the smoke goes away after about 7-8 runs.
Many people ask about the cool down, and if it
means "heat cycling" the engine.
No, the above "cool down" instructions only apply if you are using a
dyno machine to break in your engine. The reason for cool down on a
dyno has nothing to do with
"Heat Cycles" !
Cool Down on a dyno is important since the cooling fans used at most
dyno facilities are too small to equal the amount of air you experience
at actual riding speeds.
This will happen to a brand new engine just as it will happen to a
very old engine.
If you're breaking your engine in on the street, the
high speed incoming air will keep the engine temperature in the
What about "heat cycling" the engine ?
There is no need to "heat cycle" a new engine. The term "heat cycle"
comes from the idea that the new engine components are being "heat
treated" as the engine is run. Heat treating the metal parts is a
very different process, and it's already done at the factory before
the engines are assembled. The temperatures required for heat
treating are much higher than an engine will ever reach during
The idea of breaking the engine in using "heat cycles" is a myth
that came from the misunderstanding of the concept of "heat
On the Street:
Warm the engine up completely:
Because of the wind resistance, you don't need to use higher gears like
you would on a dyno machine. The main thing is to load the engine by
opening the throttle hard in 2nd, 3rd and 4th gear.
Realistically, you won't be able to do full throttle runs even in 2nd gear
on most bikes without exceeding 65 mph. The best method is to
alternate between short bursts of hard acceleration and deceleration. You
don't have to go over 65 mph to properly load the rings. Also,
make sure that you're not being followed by another bike or car when you
decelerate, most drivers won't expect that you'll suddenly slow down, and
we don't want anyone to get hit from behind !
The biggest problem with breaking your engine in on the street (besides
police) is if you ride the bike on the freeway (too little throttle = not
enough pressure on the rings) or if you get stuck in slow city traffic.
For the first 200 miles or so, get out into the country where you can vary
the speed more
and run it through the gears !
Be Safe On The Street !
Watch your speed ! When you're not used to the handling of a new vehicle,
you should accelerate only on the straightaways, then slow down extra
early for the turns. Remember that both hard acceleration and hard engine
braking (deceleration) are equally important during the break in process.
Yeah - But ...
the owner's manual says to break it in easy ...
Notice that this technique isn't "beating" on the engine, but rather
taking a purposeful, methodical approach to sealing the rings. The logic
to this method is sound. However, some will have a hard time with this
approach, since it seems to "go against the grain".
The argument for an easy break-in is usually: "that's what the manual
Or more specifically: "there may be tight parts in the engine and you
might do damage or even seize it if you run it hard."
Due to the vastly improved metal casting and machining technologies which
are now used, tight parts in new engines are an extremely very rare
occurrence these days. But, if there is something wrong with the engine
clearances from the factory, The real reason ?
So why do all the owner's manuals say to take it easy for the first
thousand miles ?
This is a good question ...
Q: What is the most common cause of engine problems ?
A: Failure to: Warm the engine up completely before running it hard !
Q: What is the second most common cause of engine problems ?
A: An easy break in ! Why?
Because, when the rings don't seal well, the blow-by gasses contaminate
the oil with acids and other harmful combustion by-products !
Ironically, an "easy break in" is not at all what it seems. By trying to
"protect" the engine, the exact opposite happens, as leaky rings continue
to contaminate your engine oil for the rest of the life of your engine !
What about running it in the garage ?
Maybe you have a new snowmobile and it's not quite winter yet, or a new
bike and it's snowing...
The temptation to fire up a new vehicle in the garage just to "hear"
the new engine run can be very strong.
This is the worst thing for a new engine, in fact, my advice is:
don't even start it up until you're ready to warm it up for the first
The reason is that brand-new rings don't seat all the way around the 360
degrees of their circumference. The gas pressure from hard acceleration
forces the rings to contact the cylinder around their entire
circumference, which is the only way the rings can properly wear into the
exact shape of the cylinder to seal the combustion pressure.
Now, imagine if the engine is run in the garage. There is no load on the
engine, so the rings are just going up and down "along for the ride". Only
a small portion of their surface is actually contacting the cylinder wall.
The ring area that does contact the cylinder wears down the roughness of
the honing pattern on the cylinder walls. Once the roughness of the
cylinder is gone, the rings stop wearing into the cylinder. If this
happens before the entire ring has worn into the cylinder and sealed, you
will have a slow engine no matter how hard it gets ridden after that