Ask a couple of mechanics in the same room about how to break in an engine and you’re likely to start a heated discussion. Engine break in is a topic with a wide variety of opinions. Each with varying degrees of validity and each based on experience. There is virtually no published widely available engineering study backing the opinions and advice so often given as gospel.
We are not here to purport that the advice given in this article is the last word. It is solely the accumulated knowledge of experience, obtaining information from manufactures such as S&S, speaking with factory team mechanics, and reading as much published text as we were able to get our hands on.
Engine break in is not something to take lightly. Whether it be a brand new Harley or a re-built Evo break in determines maximum horsepower the engine can generate and the amount of oil the engine will consume. The initial five hundred miles of an engine‘s life have a major impact on how the engine will perform and ultimately the life of the engine.
First a little background. Break in is the process of seating the compression rings to the cylinder walls. It is the physical mating of the engine’s piston rings to it’s corresponding cylinder wall. Achieving a good compatible seal between the piston rings and the cylinder wall is done through the initial wearing of the rings and cylinder. In turn this reduces the amount of combustible gases escaping the combustion chamber past the piston rings into the crankcase section of the engine.
The term blow by was coined to refer to the escaping gas. Reducing blow by enables the engine to run cleaner and cooler. 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. The piston rings serve a few purposes. Among these purposes is managing the amount of oil present on the cylinder walls and sealing the gases within the combustion chamber. Without the rings seating properly excessive amounts of oil will accumulate on the cylinder wall surfaces. Every time the cylinder fires this oil is burned. Add to this blow by induced engine breathing and you have the engine consuming oil.
Breaking in an engine is a process. Manufactures by there very nature are very conservative in their advice. They also tend to keep it simple which for a lot of things in life is usually good. Manufacturers advice on break in, with minor variation, is to keep the RPM low for the first 1000 miles, change the oil after 1000 miles, and then gradually raise the RPM In our opinion lugging an engine by keeping the RPM too low is equally bad if not worse then the advice to run the engine as hard as you usually do when riding.
Lugging the engine or using low power will not expand the pistons rings to the degree required to avoid forming a film on the cylinder walls. This film is referred to as glazing and the only method to remove it is to re-hone the cylinders by removing them. This can be a very expensive job. The break in process stops with the result of excessive oil consumption when the cylinders are glazed.
Engine break in is separated into two parts. Initial pre-ride and the first 1000 miles. To ensure the head gaskets do not fail the initial start up is important. Run the engine approximately one minute at 1250-1750 rpm. Do not crack throttle or subject the engine to any loads during this period. Check the oil pressure and ensure it is normal. Verify oil is returning to the oil tank, and that no leaks exist. Shut off the engine. Check for leaks or other problems. It is important to let engine cool to the touch. After engine has cooled, start up again and allow the motor to build some heat. Engine should be run no longer than three to four minutes. When the cylinders become warm or approximately 150 degrees shut the motor down and let it cool to room temp. Check for leaks and verify oil is returning to the oil tank.
Repeat this procedure 3 or 4 times. Each successive time let the engine run a little hotter, may 10 degrees or so. Apply a little more throttle each run up to 2500 on the last cycle. If running a carbureted bike do not attempt to set the best idle speed and mixture at this time. Get these setting close. Until the engine is operating at normal running temperatures these setting can not be dialed in.
Also do not let the engine temperature become excessive. For most garage mechanics as my wife says, take it outside. After the last cycle allow the engine to cool to room temperature. Check for leaks.
Your bike is now ready for the second part of the break in. The first 1000 miles is what most people think of when breaking in a bike. This is because the dealer has already performed the preliminary break in.
The most crucial part of the break in is the first 50 miles. It is during these miles that engine damage will occur if not ridden properly. First and foremost do not exceed 2500 RPM and do not lug the engine for the first 50 miles. In other words stay in the lower gears. Vary the RPM. Vary the load. Do not hold the RPM steady for any length of time. Stay off the freeway. If it is really hot day wait till it cools down. Excessive engine temperature is damaging. A common myth is that using synthetic oil during breaking reduces the necessary wearing. This has not been proven. After the first 50 miles change the oil to remove any debris.
Run the engine no higher than 3500 RPM for the next 500 miles. Again vary the RPM and load. Avoid steady speeds and do not lug the engine. After 500 miles we recommend changing the engine oil, transmission oil, and primary oil if running a wet clutch.
The next 500 miles increase the RPM without hitting the rev limiter. Continue to vary the RPM and be conservative. Operate at normal highway speeds. Do not engage in drag racing, dyno runs, and excessive speeds. After 1000 miles if you have a carbureted bike check the jets and make appropriate adjustments.
Change the engine oil. Your engine is now broken in.
Mark Nemets, Axiom Cycles