Crankshafts

Which stroke should your engine project be built around, and can your current crankshaft handle more boost and higher revs? This category brings together crankshafts, crankshaft kits and related parts such as crank hubs for you who are rebuilding an engine or building it up for more power.

The role of the crankshaft in the engine

The crankshaft converts the up-and-down movement of the pistons into rotation, and its stroke, together with the bore, determines the engine's displacement. With more power, higher boost or more revs, the load increases, and the stock crank can become the weak link. Under crankshafts you will find, for example, lightweight cranks in 4340 billet steel from Brian Crower and crankshaft kits from Wiseco, while crankshaft hardware includes crank hubs from ATI, among other things. Hot Rods and S&S Cycle are also among the brands in the category.

How to choose a crankshaft

The right choice depends on several factors, not just the material:

• Engine code and model year: the crank must fit your specific engine. Check the part number, bearing dimensions and any differences between model years.
• Stroke: a changed stroke places new demands on connecting rods and pistons and piston rings, which must be matched to the crank.
• Material and manufacturing: forged steel and billet are typically chosen for high loads, but the need depends on power goals, revs and use.
• Weight: a lightweight crank can make the engine respond faster to the throttle, but it also affects how the engine runs and how it works with the flywheel.
• Balancing: a new crank may require the entire rotating assembly to be balanced together.

Installation and maintenance

Bearing clearance should be measured during installation, and new bearings selected based on the measured values. End play, torque specs and correct installation of the crank hub and harmonic damper also matter for the crank's service life. Scoring on the journals can be caused by dirt or insufficient lubrication, so the engine should be cleaned thoroughly and the oil system checked before the new crank is installed.

Frequently asked questions

What is the difference between a forged and a billet crankshaft?

A forged crank is formed from heated steel under high pressure, while a billet crank is machined from a solid block of steel. Which type suits you depends on the engine, power goals and use.

Do connecting rods and pistons need to be replaced along with the crankshaft?

Not necessarily. If you keep the stroke, existing parts in good condition can typically be reused. If the stroke is changed, connecting rods and pistons normally need to be matched to the new crank.

What is a crank hub used for?

The crank hub sits at the end of the crankshaft and typically connects the crank to the pulley or harmonic damper. ATI offers versions with one or two keyways, so choose based on your engine and the damper you use.

How do I detect wear on the crankshaft or bearings?

Typical signs are knocking from the bottom end of the engine, dropping oil pressure and metal particles in the oil or oil filter. The cause can be both worn bearings and a damaged crank, so the engine should be taken apart and measured.