Cracked connecting rods: technology you want in an engine

Cracked connecting rods sound like something one wouldn’t want in an engine, but automotive performance enthusiasts know that it’s a way to make the connecting rod assembly stronger and the engine more durable under stress.

Here’s how it works: The connecting rods are what turns the linear motion of a piston sliding up and down in a cylinder to the revolving motion needed to make a wheel go around. If you slide your fist back and forth while making circles with your elbow, your forearm is the connecting rod.

Traditionally, the “big end” of the connecting rod, the end that connects to the crankshaft (the thing that goes round and round that your elbow is connected to) is made in two pieces—the connecting rod and the cap—so it can be clamped around the crankshaft throws (where on the crankshaft your elbow attaches to).

For the cracked connecting rods, the connecting rods are forged as a single piece and then cracked apart (along a pre-configured line). When bolted back together, the irregular surfaces mate together to make a stronger joint. Eliminating pins in the assembly makes the connecting rod lighter as well, which has multiple benefits.

Cracked connecting rod technology is used in the 1.8-liter Honda Civic engine among others. It’s more expensive but it’s something you really do want in an engine.

cracked connecting rod illustration

Illustration by Honda