This is why I almost never post in these types of threads. There is ALWAYS heavy opposition to this type mindset and an unwillingness to investigate.
Originally Posted By: BigCahuna
I'll bet the conversation between you and your rebuilder would go something like this. After you inform your rebuilder that your motors not running right, they inspect it and ask if you followed their break-in procedure. You say no, I did what that motoman said, and broke it in hard like he said to. They would in turn say to you, then have HIM fix it then. I tend to follow what a company with thousands of motors under their belt,says to do then what some guy on the internet with a hundred or so motors under his belt has to say. What does he care if YOUR motor goes bad?.,,
Not running right? Could you elaborate? Yes, of course telling them that I gave it a vigorous break in could end up with them not wanting to help. But it would be done arbitrarily - without any real investigation or fact finding.
Have you actually read the content of the articles?
While I don't have inside info on auto makers, I do have inside info on what John Deere does in their dyno test cells. Yes, it's a diesel, but the same principles apply... Guess what? they bring them to temp and flog them to WOT. This comes from a guy who worked the dyno cells at the Deere engine works plant in Waterloo Iowa.
Much of today's mind set is borrowed from yesterday's wisdom, when machining quality, techniques and materials wasn't as good as it is today. BUT, THINGS HAVE CHANGED, and still yesterday's mind set remains. What does it actually hurt? Nothing. BUT, the ring seal won't be optimal.
If an engine is going to have problems, it's going to have problems no matter how you break it in. There is no "wearing together of parts". If bearings are rubbing journals to the point of needing to be cautiously and gently operated, it's a bad thing. I've seen (personally) and read of countless other performance gas engines that are brought to temp on the dyno and flogged through various load cycles with no ill affect. I have even seen them torn back down after use in their end use vehicle and again, they were fine. In fact if you were to measure bearing clearances before putting a new engine into service and after 20k miles, you'd be hard pressed to find any difference. This, of course is ASSUMING accurate machine work and clean and correct assembly.
I have built numerous 2 cycle engines (yes, it's applicable - they still have pistons, rings and cylinder walls as well as a need for ring seal) and can attest to a vigorous break in vs. an easy one. The level of ring seal is quite evident. Both quantifiable (measured compression) and visually (blow by). Also, amazingly, the pistons didn't self destruct. If you like, I can provide pictures (my own) to illustrate the differences.
Bottom line... IF the machine work is accurate and the [engine] assembly is proper, then the engine will live a long life REGARDLESS of break in procedure. But a "hard" break in assures better ring seal than an "easy" break in.