Just thought I would add this post I wrote for the COG. After reading all the break in misguided information, I thought some facts about what happens in the first hours of new bike ownership might be interesting.
Happy reading.
The biggest myth expounded on motorcycle forums and new bike manuals is the need for easy break in. Mostly it is thought that that crank/rod bearings, trans. bearings and gear surfaces require a certain amount of break in before you can ride it like it was designed. I'v read these posts and manuals time and time again and there are some incorrect assumption.
Babbit bearings that are used on most modern day crankshafts and connecting rods (except HD engines) DO NOT REQURE ANY BREAK IN. Bearing are designed to run on a film of oil that cannot be compressed. Any extended metal on metal contact, except at rest, would destroy the bearing surface, main or rod. This is why most engine wear occurs at startup. In addition, the surface of a babbit bearing is as soft as lead. The purpose of this soft metal layer is so that any minute metal fragments in the oil supply not filtered will hopefully embed into the soft bearing surface and remain there, leaving the crank unharmed.
Ball bearings found in transmissions (and HD connecting rods) are among the most closely dimensioned parts in the world of manufacturing. The balls and races are polished to 1micro inch or 1,000,000th inch tolerances. There is NO BREAK IN REQUIRED ON ANY ROLLER BEARING.
Even gears and valve seats are so finely polished in today's manufacturing techniques they require NO BREAK IN.
Due to the vastly improved metal casting and machining technologies which are now used, tight parts in new engines are not normal. A manufacturing mistake causing a tight clearance, or out of spec part, is an extremely rare occurrence. But, if there is something wrong with the engine clearances from the factory, no amount of gentle running-in will fix the problem.
The only break in on a modern engine is piston ring to cylinder wall. The very reason the cylinders are cross-hatched honed is to facilitate mating of the ring and cylinder wall and provide the tightest possible seal in the combustion chamber. The majority of this seal, whether successful or not, happens in the first 50 miles or so of riding. The tighter the seal the higher the compression the more power and less oil loss and contamination.
Contrary to popular belief, piston rings don't seal the combustion pressure by spring tension. Ring tension is necessary only to "scrape" the oil off the cylinder walls to prevent it from entering the combustion chamber when not under any load. The rings seal from the actual combustion gas pressure itself !! The pressure gets behind the rings forcing them outward against the cylinder wall.
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. If the rings aren't forced against the walls soon enough, they'll use up the cylinder wall roughness before they fully seat.
With less than a perfect seal in the combustion chamber you have less compression and power, and a lifetime of leakage contaminating the oil with blow-by gasses which contain acids and other combustion by products. A badly leaking cylinder will eventually burn a piston skirt and cause scuffing and cylinder wear.
And it wouldn't hurt to do an extra oil change very early, like after the first 50-100 miles. With the metal being scrubbed off the cylinder walls and rings, the last thing you want is that metal floating around your engine. The cam chain will act as a conveyor belt moving that contaminated oil up into the valve train. Not a good thing. Worth the extra couple of bucks. And stick with Kawi petroleum based oil for at least the first couple of oil changes before, and if, you switch to synthetic.
Hard break in (not following the owners manual break in instructions) may seem controversial and will test a persons knowledge of the physics involved. Easy break ins will not necessarily harm an engine, but from the standpoint of power and durability race teams will always use the hard break in rule where seconds and a couple of extra HP make the difference between winning and losing a race and durability may mean a winning or losing race season.
My personal take on easy break ins has more to do with manufacturer's liability. Getting used to the power of a new motorcycle over time is certainly a safer way to break in a new rider.
