There’s a reason new motors are ‘tight” and not as responsive as ones that have had several miles put on them and that’s because all the moving parts haven’t “broken-in” yet. Friction is a key factor in a new motor because of how tight everything fits together and with a high amount of friction, you end up with a loss of power.
A new motor will actually work against itself until all the internal moving parts develop the wear pattern of least resistance. Because of the tight fits of the components there’s friction and friction produces heat, which in turn causes the motor to expand which causes the parts to work against each other instead of functioning in a smooth uniform way.
If you’ve just bought a new motorcycle or have installed a new motor in the one you currently own, if you start running it real hard without going through the “break-in” process, you will cause the engine to produce excess amounts of friction and heat, the number one enemy of an air cooled engine. These two elements will shorten the life of all the moving parts inside the motor and end up producing a significant amount of metal filings and grindings within the motor and that’s not a good thing.
This is the reason that someone who has taken a brand new engine and rides the crap out of it may initially experience better performance than someone who takes the time to follow a proper break-in process because the carefully broken in motor is still developing a minimum resistance wear pattern.
So which motor will last longer? Which one is faster? A correctly ridden V-Twin custom motorcycle or Harley Davidson really doesn’t get completely broken in until somewhere between 5,000 and 10,000 miles. At that point, you’ll start to notice your bike will pick up speed and power because the friction on the internal parts has been gradually and carefully reduced as much as possible setting the stage for a long lasting motor.
On the other hand, the motor that has been run hard will still be running good and loose, but you can bet components such as piston rings to cylinder walls and valve to valve seat fitment is going to be aging well before its time and this will cause less compression which will affect the performance. It may not happen at 10,000 miles or even 20,000 miles, but it will happen much sooner that a properly broken-in motor.
You probably know the general rule of thumb is to ride a new motorcycle or new engine replacement at least 500 miles for the initial break-in. But the break-in process can actually happen in as little as 100 miles or as much as 800 miles depending on the metallurgy of the internal components, the type of oil used and what your riding habits are.
If you ride your motorcycle at a constant speed during the break in period, it’ll cause the rings to glaze and lose their sealing qualities. What you should do is slowly increase and decrease the revs as you go through the gears. It takes some patience to do this for 500 miles, but it will work out for you much better in the long run.
Another thing you want to try to avoid is letting a new motor sit and idle especially on a hot day. Keep in mind that the V-twin motor is air-cooled and with all the excess heat being generated from the break in of new components, you need to keep air flowing over those cooling fins. If you live in an area where it’s real hot you may want to consider night riding for your break in period. The key thing is to just use some common sense in how you treat your bike. Take care of it and it will take care of you!