What we have to think about here is the basic theory of a two-stroke engine. Remember that the spark-plug fires once every revolution in a two-stroke engine and not every two revolutions like a four-stroke. Because of this, the fuel and air in the cylinder are compressed, and when the spark plug fires the mixture ignites. This resulting explosion drives the piston downward and as the piston moves downward, it is compressing the air/fuel mixture in the crankcase. As the piston approaches the bottom of it's stroke, the exhaust port is uncovered and the pressure in the cylinder drives most of the exhaust gases out of the cylinder. Once the piston finally bottoms out, the intake port is uncovered. What this does is pressurize the mixture in the crankcase, so it rushes into the cylinder, displacing the remaining exhaust gases and filling the cylinder with fresh fuel. Now the momentum in the crankshaft starts driving the piston back toward the spark plug for the compression stroke. As the air/fuel mixture in the piston is compressed, a vacuum is created in the crankcase. This vacuum opens the reed valve and sucks air/fuel/oil in from the throttle body. Once the piston makes it to the end of the compression stroke, the spark plug fires again to repeat the cycle all over again. It's called a two-stoke engine because there is a compression stroke and then a combustion stroke with a vacuum and a pressurization of the cylinder in one revolution. With understanding how a two-stroke works, it is pretty easy to assume there is not pushing and pulling of air or oil in that center cavity, otherwise it would affect the opposite cylinder and they would not be able to counter-act each other. Am I saying there is no seepage at all between the inner bearings, no. What I am saying is I can't see those inner bearings relying on any oil being pulled into them through that center cavity, or the theory of it being a two-stroke wouldn't work. In my testing of the stock oil pump on the bench, I found that the lower banjo fitting supplying this center cavity drips about 1/20th the amount of oil or less the injection fittings do. My conclusion, for what it is worth, is that it is important to get some type of lube in that center cavity to lube the gears and possibly the shaft bushings, but by no means lubes the inner crank bearings to the degree that it is detrimental to the engine for these bearings to survive. Like I said in my post above, to be on the safe side, I am installing a small bottle that will provide oil to this center cavity. Do I need it? Who knows. I believe it is still unconfirmed, but it is certainly a cheap insurance to me.
Aaron
