Cummins Factory Wholesale Crankshaft Gear 3628798 Part Crankshaft Cummins K38 KTA38 Diesel Engine Parts Machinery

A gear that transmits power from the crankshaft to the camshaft is doing something more fundamental than turning a shaft. It's dictating when every valve opens and closes. It's the metronome that keeps 12 or 16 cylinders breathing in sequence.

In a K38 or KTA38 engine, that metronome beats at 1,800 rpm. Thirty times a second, the crankshaft gear tells the camshaft gear-and through it, every valve, every injector, every combustion event-exactly when to fire-. Miss that timing by a fraction of a degree, and the engine doesn't just lose power. It loses rhythm. It knocks. It smokes. It fails-.

The 3628798 is the gear that keeps that rhythm. It's not a generic spur gear. It's a timing instrument machined to tolerances that would be excessive in any other application.

The Material – Three Layers, Three Functions

The 3628798 isn't made from one material. It's a tri-metal stratified construction-1.

The base material is vacuum-degassed SAE 8620H alloy steel with a grain size of 6-1. Why does grain size matter? Finer grain means tighter grain boundaries. Tighter boundaries mean cracks have to work harder to propagate. In a gear that sees billions of stress cycles, that's the difference between 10,000 hours and 5,000.

The bronze overlay isn't a coating-it's a bonded layer that actively reduces friction between meshing teeth. And the indium plating? That's for the marine guys. Fifteen years of saltwater exposure without corrosion means this gear survives in engine rooms where the air is thick with salt mist-1.

The Verification – Not Lab Conditions. Real Hell.

The 3628798 has been tested in conditions that would destroy lesser components-1:

Tropical rainforest power station – 100% humidity, 20,000 hours continuous operation. Tooth wear: <3 μm-1. That's less than the thickness of a human hair, after two years of running in a steam bath.

Polar icebreaker – Cold start at -50°C. Impact toughness: AKV ≥55 J-1. At -50, most steels turn brittle as glass. This gear stays tough enough to absorb the shock of meshing teeth in a frozen engine.

Copper ore crusher – Dust concentration of 1,000 mg/m³-that's not dust, that's a dust storm. Gearbox cleaning cycle: extended to 5,000 hours-1. The DLC coating and indium plating keep the gear running in an environment that would lap an uncoated gear to death in weeks.

A timing gear doesn't leak. It doesn't make noise-until it's too late. It doesn't give you a dashboard light.

It fails by gradual wear that shifts timing by fractions of a degree. The engine runs a little rougher. Fuel consumption creeps up. Power drops off. The operator notices nothing-until one day, the engine won't start, or it starts knocking, or it throws a valve through the cylinder head.

The 3628798 prevents that. Not with "high-quality materials" as a vague promise. With AISI 4140/SAE 8620H base, CuPb22Sn4 bronze overlay, indium plating, deep carburisation to 2.2 mm, DLC + MoS₂ coating, laser micro-pits, AGMA Q13 accuracy, 7× pitting resistance, -50°C toughness, and 20,000-hour humidity testing.

It doesn't just turn the camshaft. It times the engine-precisely, reliably, for the life of the engine.

For OEM specifications, torque procedures, and compatibility verification, consult your Cummins parts manual or authorised distributor.