Crankshafts
About Crankshafts
The crankshaft turns the up-and-down motion of the pistons into the rotation that drives the transmission. Its bearings and seals wear over time, and a crank that is bent, has worn bearings or leaking seals causes vibration, noise, oil leaks and eventually failure. Riders replace a crank in a bottom-end rebuild or choose a different one to change the engine's stroke.
The first choice is the crank assembly itself, offered as OEM stroke, which restores the original specification, or stroker, which has a longer stroke and raises displacement. A stroker crank is normally paired with matching pistons and cylinders, so confirm what the listing requires. Bottom end kits combine a crank with other parts for a full refresh, and the contents are listed per model. If the crank is sound and only the bearings and seals are worn, a crankshaft bearing and seal kit is the simpler fix. Listings cover Honda, Yamaha, Kawasaki, Suzuki and Arctic Cat models, and each is made for a particular engine and year range.
Brands in this category include Athena, Hot Rods, HardDrive, ProX and All Balls. Related categories are Connecting Rods & Parts, Engine Bearings and Engine Crankcases. The full group is Engines & Engine Parts. Pick your machine in the Ride Finder at the top of the page.
FAQs on motorcycle crankshafts
What does a crankshaft do?
A crankshaft converts the straight-line motion of the pistons into rotation. The connecting rods attach to it, and it passes that rotation on to the clutch and transmission. It runs on bearings and is sealed at each end to keep oil in.
What is a stroker crankshaft?
A stroker crank has a longer stroke than the original, so each piston travels farther and the engine displaces more. It changes how the engine behaves and normally needs matching pistons and sometimes other parts. Follow the maker's listing for what else is needed.
Which symptoms point to worn crankshaft bearings?
Signs include a rumbling or knocking noise from the bottom of the engine, vibration, excess play when you move the crank by hand and metal in the oil. Seal leaks at the crank ends are another sign. Have the bottom end inspected before using the bike.
Is a bottom end kit the same as a crankshaft?
Not exactly. A bottom end kit combines a crankshaft with related parts for a rebuild, and what is in it varies by model, so read the listing. A crankshaft assembly is the crank itself.
Can I replace the crankshaft myself?
It is advanced work. The engine has to be removed and the crankcase split, and the crank needs correct alignment and tolerances. Many riders have a shop do it. Use your service manual for procedures, and replace the bearings and seals at the same time.
