Crankshafts
About Crankshafts
The crankshaft is the engine's main rotating shaft, and it turns piston motion into the power that drives the machine. It runs on main bearings and carries the connecting rod. Owners replace one for a knock from the bottom end, a bent shaft, worn bearing journals, or as part of a full rebuild.
Listings come in three common forms. OEM-stroke assemblies keep the stock stroke and are the usual like-for-like replacement. Stroker assemblies have a longer stroke to increase displacement, and they need matching pistons and cylinders and often a tune, so they are not a direct swap. Smaller kits, such as bearing and seal kits and a crankshaft and rods kit, refresh a crank or supply one with rods fitted. Check which one the listing is, and measure end play and runout against your manual's limits when the engine is apart.
Brands in this category include Hot Rods, Prox, All Balls and Wiseco. Pick your machine in the Ride Finder at the top of the page. Cranks are usually fitted with new Engine Bearings and Gaskets, Seals & Kits, and Connecting Rods & Parts, Pistons, Rings & Piston Kits and Engine Rebuild Kits & Components are close by, in Engines & Engine Parts.
FAQs on crankshafts
What is a stroker crankshaft?
A stroker crankshaft has a longer stroke than the original, which increases the engine's displacement. It needs a matching piston and cylinder setup and usually a tune. It is a performance modification, not a like-for-like replacement for a stock crank.
How do I know if my crankshaft is bad?
Signs include a knocking or rumbling noise from the bottom end, vibration, metal in the oil, and play in the shaft. A bent crank can also be found by measuring runout. If you suspect a crank problem, stop riding and inspect it before it damages the cases.
Do I need new bearings with a new crankshaft?
Usually yes. Fresh main bearings and seals go with a new or rebuilt crank, and bearing and seal kits are listed for many machines. Fitting new bearings and seals to a worn case or shaft journal will not last, so inspect those too.
What does OEM stroke mean?
OEM stroke means the crank has the same stroke as the factory original, so the engine keeps its original displacement. It is the right choice if you want a standard replacement rather than a change in engine size.
