New Engine Break-in Procedure
This is a summation of many articles on the subject
found on the internet. Some of the information is from MOTORCYCLIST Feb.
1991, titled GIVE IT A BREAK-IN (How to make your bike run stronger and
live longer), and some is from a Textron Lycoming "Key
The first few hundred miles of a new engine's life
have a major impact on how strongly that engine will perform, how much
oil it will consume and how long it will last. The main purpose of
break-in is to seat the compression rings to the cylinder walls. We are
talking about the physical mating of the engine's piston rings to it's
corresponding cylinder wall. That is, we want to physically wear the new
piston rings into the cylinder wall until a compatible seal between the
two is achieved.
Proper engine break in will produce an engine that
achieves maximum power output with the least amount of oil consumption
due to the fact that the piston rings have seated properly to the
cylinder wall. When the piston rings are broken in or seated, they do
not allow combustion gases to escape the combustion chamber past the
piston rings into the crankcase section of the engine. This lack of
"blow-by" keeps your engine running cleaner and cooler by
preventing hot combustion gases and by-products from entering the
crankcase section of the engine. Excessive "blow-by" will
cause the crankcase section of the engine to become pressurized and
contaminated with combustion gases, which in turn will force normal oil
vapors out of the engine's breather, causing the engine to consume
excessive amounts of oil.
In addition to sealing combustion gases in the
combustion chamber, piston rings must also manage the amount of oil
present on the cylinder walls for lubrication. If the rings do not seat
properly, they cannot perform this function and will allow excessive
amounts of oil to accumulate on the cylinder wall surfaces. This oil is
burned each and every time the cylinder fires. The burning of this oil,
coupled with "blow-by" induced engine breathing, are reasons
that an engine that hasn't been broken in will consume more than its
share of oil.
However the ring will only ride on this film of oil
if there is sufficient surface area to support the ring on the oil. When
the cylinders are freshly honed the peaks are sharp with little surface
area. Our goal when seating the rings on new steel cylinders is to
flatten out these peaks to give more surface area to support the rings,
while leaving the bottom of the groove intact to hold enough oil to keep
the surface of the cylinder wet with oil. See illustration. At the point
where the top of the peaks produced by the honing operation become
smooth and the tapered portion of the piston ring wears flat break in
When a cylinder is new or overhauled
the surface of it's walls are honed with abrasive stones to produce a rough
surface that will help wear the piston rings in. This roughing up of the
surface is known as "cross-hatching". A cylinder wall that has been
properly "cross hatched" has a series of minute peaks and valleys
cut into its surface. The face or portion of the piston ring that interfaces
with the cross hatched cylinder wall is tapered to allow only a small portion
of the ring to contact the honed cylinder wall. When the engine is operated,
the tapered portion of the face of the piston ring rubs against the coarse
surface of the cylinder wall causing wear on both objects.
Each tiny groove acts as the oil reservoir holding oil up
to the top level of the groove where it then spreads over the peak surface.
The piston ring must travel up and down over this grooved surface, and must
"hydroplane" on the oil film retained by the grooves. Otherwise, the
ring would make metal-to-metal contact with the cylinder wall and the cylinder
would quickly wear out.
When the engine is operating, a force known as Break
Mean Effective Pressure or B.M.E.P is generated within the combustion
chamber. B.M.E.P. is the resultant force produced from the controlled
burning of the fuel air mixture that the engine runs on. The higher the
power setting the engine is running at, the higher the B.M.E.P. is and
conversely as the power setting is lowered the B.M.E.P. becomes less.
B.M.E.P is an important part of the break in
process. When the engine is running, B.M.E.P. is present in the cylinder
behind the piston rings and it's force pushes the piston ring outward
against the coarse honed cylinder wall. Piston rings are designed to
take advantage of the pressure and us it to push the rings out against
the cylinder wall. Therefore, as pressure builds during the compression
stroke, the rings are pushed harder against the cylinder wall which aids
in seating the rings.
The higher the B.M.E.P, the harder the piston ring
is pushed against the wall. The surface temperature at the piston ring
face and cylinder wall interface will be greater with high B.M.E.P. than
with low B.M.E.P. This is because we are pushing the ring harder against
the rough cylinder wall surface causing high amounts of friction and
thus heat. The primary deterrent of break in is this heat. Allowing to
much heat to build up at the ring to cylinder wall interface will cause
the lubricating oil that is present to break down and glaze the cylinder
wall surface. This glaze will prevent any further seating of the piston
rings. If glazing is allowed to happen break in will never occur. Also,
if too little pressure (throttle) is used during the break-in period
glazing will also occur.
Most people seem to operate on the philosophy that
they can best get their money's worth from any mechanical device by
treating it with great care. This is probably true, but in many cases it
is necessary to interpret what great care really means. This is
particularly applicable when considering the break-in of a modern,
For those who still think that running the engine
hard during break-in falls into the category of cruel and unusual
punishment, there is one more argument for using high power loading for
short periods (to avoid excessive heat) during the break-in. The use of
low power settings does not expand the piston rings enough, and a film
of oil is left on the cylinder walls. The high temperatures in the
combustion chamber will oxidize this oil film so that it creates glazing
of the cylinder walls. When this happens, the ring break-in process
stops, and excessive oil consumption frequently occurs. The bad news is
that extensive glazing can only be corrected by removing the cylinders
and rehoning the walls. This is expensive, and it is an expense that can
be avoided by proper break in procedures.
We must achieve a happy medium where we are pushing
on the ring hard enough to wear it in but not hard enough to generate
enough heat to cause glazing. Once again, if glazing should occur, the
only remedy is to remove the effected cylinder, re-hone it and replace
the piston rings and start the whole process over again.
We asked four top motorcycle engine builders what
they do to ensure peak power output and optimum engine life. Here is a
capsulation of their responses.
"If the wrong type of oil is used initially, or
the break-in is too easy, rings and cylinders could (read will) glaze
and never seal properly. A fresh cylinder wall needs some medium to high
engine loading to get the piston rings to seat properly for good
compression but make sure you don't lug or overheat the engine. Use high
quality, low viscosity oil (Valvoline 30 weight), no synthetics, too
slippery. If synthetics are used during initial break in the rings are
sure to glaze over.
An engine's initial run should be used to bring oil
and coolant (air, oil, and/or water) up to operating temperature only,
with little or no load, then shut down and allowed to cool to ambient
temperature. This is important. After each run the engine needs to
completely cool down to ambient temperature. In Texas, especially in the
summer, that's still pretty hot. After a cool down period, start it up
again and take the motorcycle for it's fist ride (you hope).
This time give the engine light loads at relatively
low rpm and stay out of top gear. Lugging the engine, i.e., low RPM with
a lot of throttle (manifold pressure), is more detrimental than high
rpm. Another key is too constantly vary engine load during the entire
break-in period. A constant load is not ideal for breaking in bearing
tolerances. This second run should last only 10-15 minutes before
another complete cool down.
The third run should see slightly higher rpm with
light to medium power loading using short bursts of acceleration to help
seat the rings. Again 10-15 minutes of running should do it and again
avoid top gear. A forth run should consist of light to medium engine
loads with a few more bursts of medium-high rpm, and lasting just 10-15
minutes varying the engine load and again avoiding top gear. Next while
the engine is still warm drain the oil and change the filter. This gets
out the new metal particles that are being worn away. Most of the metal
particles will break away within the first 50 -75 miles. To ensure the
rings seat well, use the same high quality oil and don't be shy about
short duration high rpm blasts through the lower gears after the oil has
A few more 15-20 minute sessions should be used to
work up to the engine's redline gradually increasing the engine loads.
After some definite hard running and 250-500 miles it's a good idea to
check the valves. After 500 miles re-torqueing the head is suggested.
Switch to synthetic oil but not before 500-1500 miles. Most of the
engine experts warned of the danger of breaking in the engine too easily
and ending up with an engine that will always run slow whether it is
from tight tolerances, inadequate ring seal or carbon buildup. Engine
load is more detrimental than rpm because of the head created
internally, so avoid lugging the engine but rev it freely especially in
the lower gears. Basically, be sure not to get it too hot but be sure to
seat the rings properly.
So that's it, sure a lot different than keeping
under 4000 rpm for 500 miles then under 5000 rpm for 1000 miles. Maybe
bike manufacturers are being super cautious at the expense of your
motor's performance? I think that they take the cautious route that
works over time (1000 miles, or about 20 hours of break in) versus a
faster route that can be more easily screwed up."
Copyright © 2000 NTNOA All rights reserved.
Revised: November 23, 2018.