Harley Davidson Engine Break In
- Part 2 -
Continued from : Part 1 of Engine Break In
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 beak in of any engine including those from S&S 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 particularly for the high performance engines of today such as S&S. 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.
To assist the wearing in of the piston rings the surfaces on new or overhauled cylinders are honed with abrasive stones.
This process of producing a rough surface on the cylinder walls is known as cross-hatching. A series of minute peaks and valleys cut into its surface exist on a cylinder that has been cross hatched.
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.
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 has occurred.
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.
- End Engine Break In -
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Back to : Part 1 of Engine Break In
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