A review of the casting design pointed to the casting gating as the primary reason for shrinkage porosity in the connecting center shaft. 

The tooling design used two gates to feed molten metal into the main cylinder on the top and into the cup on the bottom.

• The thick center shaft was remote from the two gate inlets with no direct metal feed into the heavy section during solidification. 

• As the thin-wall cylinder on the top and cup on the bottom solidified, metal feed into the center shaft was restricted and porosity shrinkage formed in the shaft.