Re: Rebuilt Engine Break in recommendations
Paul, If you must know, here is an article from a pro ( George Van Parys ) hope it helps;<br /><br />Breaking in a New or Rebuilt Engine<br /><br />Whenever an engine's piston rings are replaced whether in part or in entirety it is necessary to break in the engine. Piston rings are replaced at a complete engine overhaul or repair, top overhaul or single cylinder overhaul or repair.<br /><br />When we refer to engine or cylinder break in, we are talking about the physical mating of the engine's piston rings to it's corresponding cylinder wall. That is, we want to physically wear the new piston rings into the cylinder wall until a compatible seal between the two is achieved.<br /><br />Proper engine break in will produce an engine that achieves maximum power output with the least amount of oil consumption due to the fact that the piston rings have seated properly to the cylinder wall. When the piston rings are broken in or seated, they do not allow combustion gases to escape the combustion chamber past the piston rings into the crankcase section of the engine. This lack of "blow-by" keeps your engine running cleaner and cooler by preventing hot combustion gases and by-products from entering the crankcase section of the engine. Excessive "blow-by" will cause the crankcase section of the engine to become pressurized and contaminated with combustion gases, which in turn will force normal oil vapors out of the engine's breather, causing the engine to consume excessive amounts of oil. In addition to sealing combustion gases in the combustion chamber, piston rings must also manage the amount of oil present on the cylinder walls for lubrication. If the rings do not seat properly, they cannot perform this function and will allow excessive amounts of oil to accumulate on the cylinder wall surfaces. This oil is burned each and every time the cylinder fires. The burning of this oil, coupled with "blow-by" induced engine breathing, are reasons that an engine that hasn't been broken in will consume more than its share of oil.<br /><br />When a cylinder is overhauled or repaired the surface of it's walls are honed with abrasive stones to produce a rough surface that will help wear the piston rings in. This roughing up of the surface is known as "cross-hatching". A cylinder wall that has been properly "cross hatched" has a series of minute peaks and valleys cut into its surface. 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. 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.<br /><br />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.<br /><br />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. 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. We must achieve a happy medium where we are pushing on the ring hard enough to wear it in but not hard enough to generate enough heat to cause glazing. If glazing should occur, the only remedy is to remove the effected cylinder, re-hone it and replace the piston rings and start the whole process over again.<br /><br />Understanding what happens in the engine during break in allows us to comprehend the ideas behind how we should operate the engine after piston rings have been changed.<br /><br />The break in process may take as long as 20 hours of operation to complete. You are in control of engine break in for 98 % of the time that it takes to occur. This is a serious responsibility when you consider the expense and aggravation of having to remove, re-hone and re-ring cylinders that have glazed and not broken in.<br /><br />Use regular oil, not synthetic, during break-in.<br /><br />When you first start it up, let it COMPLETELY warm up, not just kinda warm, all the way warm. Liquid cooled engines require that the engine be brought gradually to normal operating temperature to avoid cold seizure resulting from pistons expanding faster than the cylinder liner.<br /><br />Allow 1 hour at idle speed only for break-in of new pistons or rings.<br /><br />While it's still hot, check and see if the head needs to be retorqued.<br /><br />Check the timing again, as well as the valve adjustment.<br /><br />DO NOT RUN ENGINE AT CONSTANT RPM FOR PROLONGED PERIODS OF TIME.<br /><br />After gradually bringing engine to normal operating temp., operate engine in gear at approx. 1500 RPM for 20 minutes.<br /><br />Operate in gear at no more than 2000 RPM for the next 60 minutes.<br /><br />Cruise at 3/4 throttle or less for the next 4 hours.<br /><br />Occasionally reduce throttle to idle speed for a cooling period.<br /><br />Use only enough throttle to plane your vessel and then throttle back to ~3000 RPM.<br /><br />Avoid operating in the 2000-3000 RPM range at all times during the 10 hour break-in period.<br /><br /> During the 6th hour of break-in, plane boat quickly and then throttle back to maintain minimum plane speed.<br /><br /> During this 6th hour, you can throttle up to 3/4 throttle for 1-2 minutes, then return to minimum planing speed.<br /><br />During the final hours of break-in you can operate at full throttle for periods of 2 minutes or less.<br /><br />Avoid continuous full throttle operation for the first 10 hours of operation.<br /><br />Change the oil after 10 hours. Still just the regular oil.<br /><br />Change the oil again after 20 hours. Still just the regular oil.<br /><br />Change the oil again (50 hours). Now you can use the expensive synthetics if you want to.<br /><br />After that, the motor is pretty much broken in, so go run the dang thing to see how fast it is!!!!
