The first time I saw .7854 I was like what the crap too, but when you do the math... Area of a circle = Pi*r^2 = Pi*(D/2)^2 = (Pi*D^2)/4 = D^2*(Pi/4) = D^2*0.7854 Then for dispacement multiply the area by stroke and # of cylinders. Displacement = 0.7854*D^2*Stroke*# of Cylinders. 0.7854 is also easy to remember cause it's a counter clockwise circle in the upper left on the calculator :Brow:
Also another viable method. I was in a time crunch and didn't have to deal with a machine shop. But still wouldn't require the use of spacers.
