on video How to change motorcycle connecting rod kit crank from Harley

 In automotive practice—and in motorcycles—a one-piece crankshaft and split-and-bolted connecting rods, with plain bearings, is the best solution.

The earliest motorcycles had five-piece crankshafts. There were two main shafts, a crankpin, and two flywheels—five pieces. The main shafts fitted into the flywheels with tapers and nuts, and the same thing for the crankpins.

The connecting rod was a one-piece affair. You assembled the bearing on to the crankpin, slid the rod on to the bearing, put the other flywheel on the end of the pin, did up the tapers and nuts, lined it all up with hammers and dial gauges, and you had yourself a crankshaft.

As you can imagine, a crankshaft being assembled from all those pieces meant there were at least that many failure modes. Very early there was a desire to simplify matters by making a one-piece crankshaft and having the connecting rod come apart into two pieces.

During the 1960s, Honda elevated the art of tiny racing engines by building 50cc twins, a 125cc five-cylinder, and 250cc and 297cc six-cylinders. All of those engines had one-piece connecting rods and crankshafts that were assembled by pressing all of these pieces together.

Honda realized that was never going to be the key to making a mass-produced product. The 1969 CB750 inline-four had split-and-bolted connecting rods and a one-piece forged steel crankshaft—very rugged. That’s the way MotoGP and Formula 1 engines are built to this day.

 In automotive practice—and in motorcycles—a one-piece crankshaft and split-and-bolted connecting rods, with plain bearings, is the best solution.

The earliest motorcycles had five-piece crankshafts. There were two main shafts, a crankpin, and two flywheels—five pieces. The main shafts fitted into the flywheels with tapers and nuts, and the same thing for the crankpins.

The connecting rod was a one-piece affair. You assembled the bearing on to the crankpin, slid the rod on to the bearing, put the other flywheel on the end of the pin, did up the tapers and nuts, lined it all up with hammers and dial gauges, and you had yourself a crankshaft.

As you can imagine, a crankshaft being assembled from all those pieces meant there were at least that many failure modes. Very early there was a desire to simplify matters by making a one-piece crankshaft and having the connecting rod come apart into two pieces.

During the 1960s, Honda elevated the art of tiny racing engines by building 50cc twins, a 125cc five-cylinder, and 250cc and 297cc six-cylinders. All of those engines had one-piece connecting rods and crankshafts that were assembled by pressing all of these pieces together.

Honda realized that was never going to be the key to making a mass-produced product. The 1969 CB750 inline-four had split-and-bolted connecting rods and a one-piece forged steel crankshaft—very rugged. That’s the way MotoGP and Formula 1 engines are built to this day.