What Is The Greatest Engine Design Advancement In The 21st Century?

Sound castings with high strength have resulted in great weight savings

I want to talk about the revolution in major castings that has taken place resulting in much lighter motorcycles than ever before. An English engineer a couple of years ago asked me to name the greatest advance in engine practice of the 21st century. As I opened my mouth and nothing much came out, he came to my rescue and said, “Lighter-weight castings” by reason of advanced casting technology.

When aluminum is melted prior to either injecting it into a die-cast mold or to be poured as a sand casting, instantly a layer of aluminum oxide forms on the top of the melt. We’re accustomed to seeing a skin form on the top of gravy when we take the gravy off the burner, and we know that if we take a spoon and stir it up the skin will disappear. But aluminum oxide is durable ceramic; it’s not soluble in molten aluminum.

If you pour liquid aluminum into a mold that highly turbulent pouring process is carrying skins of aluminum oxide into the casting, where they will form zones of weakness when it solidifies. Another English engineer devised ingenious methods of avoiding the entrainment of these films. Filling the mold gradually from the bottom causes those lightweight ceramic skins floating on top of the rising metal to be pushed out vent holes at the top of the mold.

When they began to cast metal in this new way, under improved control, they found that it didn’t take as much metal to achieve the desired strength. All modern motorcycle engines—and indeed the cast frames that most motorcycles now have—are able to achieve amazingly thin sections and have the part be actually stronger than it was in the massive crankcases of yesteryear.