There are two sources for oil to get up from the crank to the piston / small end. The main bearings and the big end. The leakage from the cam chain sides of the mains goes either up the cam chain tunnel or down to the oil pump.
Anything on the big end side of the main bearings gets flung up to the big end (on the hollow inside of the pin) so that leave only one source.
Doing a little math on the possible escape routes, which all have the same pressure oil behind them.
a) the side of the big end
b) the slots cut into the big end
Taking the sides first. The bore of the con-rod is 31 mm so the curcumference is PI x D which is about 97.5 mm. To get the area of the escape path we need the side clearance of the rod. I set mine to around 3-4 thou (0.003-0.004 inch). I know that Jerry uses around 9 to get more oil flowing out but I think 4 is about right for a road engine.
Consider 4 thou or 0.101mm clearance. That gives an escape area of 9.7 square mm. You can share that between the two faces of the rod but it is the same figure.
Now, taking the 12 O'clock slots in the later rod (right picture) which are around 5.5mm wide by 2mm deep, that gives an area of 11 sq mm each but there are two vertical slots per rod so that is 22 square mm.
That means that 2 1/4 times as much oil is directed upwards toward the small end than escapes randomly past the rod faces. Closer clearances at the sides of the big-end means that even more goes up top where it can do something useful. If you could run with 1 thou side clearance, more would go to teh small end.
Is that a significant amount?
When I have a moment, I'll build a test rig and measure it and the flow from good / bad pumps.
Regardless of all this, the cleaner you can get the insides of a used crank, the longer it will last..... :-)
Have fun at the Barber Vintage Festival. I'll be on a plane to New York but I shall be back home for the Stafford Classic Bike Show.
G
LOUD MOUSE wrote:I'm on my way to BARBER and will read your reply when I return.
A quick look still didn't seem to explain your idea that any real amount of oil is sent to the bottom of the piston from the design of the big end of the rod.
I didn't include the oil path to the center bearings as that is very visible as one looks at the cases and outer race of the center bearings.
I'm respond more when I return. ...............lm