Mister Tee
03-27-2008, 12:12 PM
As many engine break-in threads as we have, we need a sticky on it for reference. So what I’m going to do, is go ahead and open this for discussion, let it run a while, and then sticky it.
Engine design has changed very little in the last 50 years. What has changed significantly is electronic engine controls, ignition systems and fuel systems, and of course oil and lubricants. What hasn’t changed significantly is metallurgy, materials, and manufacturing techniques. Engine parts have been typically machined to tolerances within 10,000’s of an inch for the last 30 years.
There are various schools of thought on engine break-in. The two basic ones are 1) Break it in per the manufacturer’s recommendations, and 2) use the “Mototune” method (http://www.mototuneusa.com). Let's talk about what happens inside the engine when its broken in:
When an engine is broken in, these four processes occur:
1. Casting defects, rough machining, and burrs wear off and go in to the oil and filter. This happens over the course of a couple hundred miles.
2. Rings are “seated”. When we talking about seating the rings, it isn’t the rings themselves that “seat”, but wear on the cylinder walls that has to happen just right or they either won’t seat, or the surface will be polished, both of which are objectionable. Steel and cast iron cylinders are honed in a cross-hatch pattern in such a way that after the rings seat and wear the cylinder wall smooth, there are still grooves remaining that can hold oil, which is critical for engine cylinder life. With aluminum engines, the same thing happens, except that it’s rough electrodeposited cylinder lining that has to wear partially to obtain a smooth surface, and provide oil control. If these wear too much, or too fast, the whole process has to be redone. This can happen in a time span ranging from an hour, to about 1,000 miles.
3. Bearing surfaces are polished and work-hardened. Journal bearings work on a combination of a hard metal/soft metal contact, and thin film lubrication. Steel crankshaft, cam shaft and connecting rod bearing surfaces are burnished and work-hardened on the surface during the initial phases of engine operation. Too high of a loading, and/or RPM on these bearing surfaces can score them before work hardening occurs. This process takes a few hundred miles.
4. Cylinder, head and crankcase castings are heat cycled. Heat cycling does two things: It changes the shape of the casting, and alters clearances, and secondly, for some alloys (both ferrous and aluminum) it also hardens and strengthens the metal. What is important here is that the engine is sufficiently heat cycled during initial break-in, while there is still a rapid rate of wear on the mating surfaces. This process typically takes several hundred miles. You don’t want to run a new engine for 500 miles straight if you can help it – you want it to cool down completely a few times.
Once these things have happened, the wear rate decreases to a very low rate, if all went well. And wear will continue throughout the life of the engine. This is actually beneficial, to a point, since mating surfaces continue to burnish and smooth themselves, and FULL OIL CONTROL is achieved. However, once clearances are lost, wear becomes detrimental. The point at which beneficial wear continues ranges from about 5,000 miles, to about 10,000 miles on most engines.
Most motorcycle, automotive and truck engine manufacturers prefer that all four of these process be allowed to play out prior to applying full power to the engine, which is why they typically specify an initial break in period ranging from 1,000 to 3,000 miles, prior to which you can apply full power and RPM to the engine.
Accelerated engine break in procedures (e.g. http://www.mototuneusa.com) are not new. Similar procedures have been researched by engine manufactures, and developed primarily as a means for breaking in new race engines. Race engines are re-built at frequent intervals, sometimes as much as every race. Because of this, standard recommended break in procedures are very inconvenient (and costly) for a race engine due to the time, fuel and distance factors. Accelerated procedures allow for processes 1 and 2 to occur, but not 3 and 4. This isn’t typically an issue for race engines, since they are rebuilt frequently anyway – or, for that matter, the majority of sportbikes which generally meet their demise in a crash before they reaches 5,000 miles. I won’t go in to detail on the procedure, you can read it in the site.
Which method do I use? I always use the manufacturer's recommended method. Deviating from that can potentially void the warranty (although establishing that might be difficult) and I want to guarantee that I have an engine that is capable of lasting 100,000 miles or more. That isn't to say you can't "Mototune" your engine and have acceptable results, but we can discuss both sides and you can choose which way to go.