Radial Engine, Master Con Rod

[skmetal7]

Hey guys, so I'm designing a 5 cylinder Radial, with a bore diameter of 1.1" and 1" stroke (might increase stroke length). I'm having trouble with the Master con rod. I'm unsure of where to put the 4 slave rod connecting points. It can't be the typical 72 degrees (360/5), since TDC and BDC isn't 72 Deg on the crank relative to the master con rod.

I've taken some pics of the assembly, and drew an approximate motion path of the 3rd con rod connection point. It's sort of an ellipse, but not quite. I've tried making the master con rod longer and shorter, and moved the connection point around, but still doesn't make a circular path.

Is this typical for this type of crank/ con rod arrangement on radial engines?