Interesting discussion - Here is some more conventional wisdom masquerading as facts - LOL
Glazing - Glazing is the deposition of oil
on the cylinder walls that becomes very hard and smooth. The problem with glazing is that the cylinder wall actually has to have some imperfection in it. Honing a cylinder is the process where cross hatching is ground into cylinder walls. The reason you don't want a smooth cylinder wall (think glass smooth) is that the oil doesn't film properly on the wall and the rings can't "scrape' the oil off the wall. This results in excess oil being left on the wall that burns in the combustion cycle. This results in high oil consumption
To avoid glazing during the break in period many overhaulers recommend not idling the engine beyond the normal warm up times, not operating the engine at full rated RPM for a set period of time and to vary the operating speeds so that the engine sees a variety of temperatures and conditons. This is also part of the process that seats the rings to the cylinder walls although with modern materials in rings and cylnders manufacturers may have different break in recommendations based on the materials used.
Coking - Coking is the biggest concern with idling any engine. Fuels are designed to burn completely at a given temperature and pressure. idling the engine is far below the operating spec of the fuel
. The fuel
actually has split seconds to burn completely - at 3,000 rpm there are 1500 combustion events
per minute or 25 per second, for a 3 cylinder engine that's about 8 combustion events
per cylinder per second. Lower rpm and lower temperatures result in the fuel not burning completely or burning too cool. Unburned fuel deposits as coke on injectors and in exhaust
cans. It can also deposit on exhaust valve stems and exhaust ports
. High rpm, pressure and temperature can often blow out or burn away light carbon deposits. A heavily coked engine can be a problem, however.
Oil Circulation - Almost every recreational engine has a constant volume / positive displacement
oil pump. That is the flow is a function of speed. Pressure is a function of resistance in the system and maximum oil pressure is a function of the bypass valve setting. This is a technology that has been around since the earliest internal combustion engines. At low rpm there is low flow and because system drag is fixed a lower pressure results. However, your manual will indicate a minumum oil pressure, usually around 10psi. Oil pressure changes over time. As the system wears, clearances between bearing races, valve components and any precision celarance items increases. When the clearance increases there is a natural escaping of oil from the lube circuit into common areas (the sump, the valve galleys etc) - Ambient and oil temperature and the viscosity of the oil can all impact oil pressure. It is not necessary but the pedantic can trend oil vs pressure over time as one indicator of engine health
. Oil SOAP (spectrographic oil analysis program) monitoring can identify metals in the oil. For a given sample the soap results can be meaningless but over time trending oil can be useful and is a common aircraft industry practice.
So my habits for a properly broken in engine are this -
At the dock
- Fire up the engine - once oil pressure is stable and the coolant
temperature starts to rise - increase to around 1,000-1,200 rpm. This gets our alternator in the charge zone. I have left the boat for up to an hour at this level.
On the hook/mooring - fire up the engine to idle. By the time I have readied the boat to get underway (3-5 minutes) drop the hook and get going. We usually try to preceed any races or events by at least 30 minutes. We will run the engine at about 3/4 power the whole time we are setting sail and goofing around. 5 minutes before the race
gun we shut down. When we are going cruising we will probably run 50% power for about 15 minutes while getting underway.
If the winds are great we occasionally run the donk 5 minutes and shut it down.
We also always have occasion at least once a month to motor
for at least an hour and often 2 at full power. It is important to work the engine hard periodically. High power operations can take care of coke depostis.
We also change the oil every 3 months regardless of hours made on the engine. Oil contaminants are the biggest killer of any engine. As my father always said - you can't hurt an engine by changing the oil.