The pin that’s mightier… - Why a broken piston pin spells disaster

“It was a catastrophic engine failure. It cracked my cylinder block, destroyed my crankshaft and several connecting rods as well as one of my cylinder heads!” The man was angry—fuming that one broken piston pin led to the total devastation of his supercharged race engine.

Two weeks earlier he had taken advice on piston pin statistics, but his advisor had made an error in his choice of wall thickness. Reckless incompetence? Maybe, but to avoid similar troubles it pays to take advice on piston pin specifications from a reputable manufacturer. Ernie Elliott, the veteran NASCAR engine builder, says “When we consider the implications of rotational and reciprocating engine loadings our greatest concerns always lie with the latter.” And oval track dirt racers using 0.165in wall piston pins know that when compression ratios approach 14:1 it’s time to increase wall thickness to 0.185in.

Since there is always a balancing act of cost-versus-benefit, we asked Andy Anderson, engineering director of Trend Performance, to tell us what’s working and what isn’t working for today’s professional racing teams.

The top contenders for honors in racing piston pin construction are chrome molybdenum, H13 tool steel, C300 and C350 maraging steels, and M2 tool steel. The black-colored DLC coating extends pin life by a factor of four or more, reducing friction and wear and virtually eliminating pin bore troubles.

“The most prevalent piston pin materials currently in use are alloy steels,” says Anderson, “particularly 4130 chrome molybdenum, and H13 tool steel. To cope with extreme loadings, professional teams are using C300 and C350 maraging steel and M2 tool steel.” Perhaps, though, the greatest advances recently in piston pin durability have been achieved by the application of diamond-like carbon coatings to the pin’s outer surfaces. Still, selecting the right material and the correct wall thickness are the first essentials.

Here as follows are the top four contenders: chrome molybdenum; tool steels, H13 and M2; and two variations of maraging steel.

Anderson opens the topic by explaining, “Chrome molybdenum 4130 is used in naturally aspirated race engines. It’s superior to the common mild steel 1018 material."

"Tool steel H13 is often the material of choice for premium piston pins. It is considered the best all around material for most applications, especially for power-adder (nitrous, turboharging,turbocharging) uses. It has also been a popular choice in Pro Stock drag racing engines.” The H13 pin has a Rockwell hardness value of Rc54. Because it tempers at around 1,000 Fahrenheit, it lends itself to DLC coating and proves superior to 4130 and the more common 9310 steel, which tempers at around 300 degrees Fahrenheit.