The first 20 minutes of run time is to break in the cam. The rest of the time is for the cylinders. There should be no break-in required on the bearings. You'll know when your cylinders are broken in when the engine stops burning oil. I burnt a quart within the first 1200 miles, I haven't burnt a drop since with over 12,000 miles on the engine. I am doing oil changes on conventional oil at 5000-6000 miles (mostly highway).