Flywheels & Flywheel Parts
About Flywheels & Flywheel Parts
The word flywheel means two different parts here. On a Harley-Davidson V-twin, the flywheel assembly is the crankshaft: a pair of flywheels joined by a crank pin that carries the connecting rods. On many single-cylinder and dirt bikes, the flywheel or rotor mounts to the end of the crankshaft, adds rotating weight and carries the magnets for the ignition and charging system.
For V-twin flywheel assemblies, the stroke is the main number: listings show 4-1/4, 4-3/8, 4-1/2 and 4-5/8 inch. Stroke and bore together set the displacement, and a longer stroke needs cylinders, pistons and clearances worked out to suit, so it is an engine build rather than a bolt-in swap. Also match the engine family and year range, such as Evolution, Twin Cam or M8, and read whether the assembly includes a sprocket bearing race. Pullers are sold by thread size, for example M16 x 1.5 or M28 x 1, which must match the thread inside the rotor. Flywheel weights add rotating mass to certain dirt bikes.
Brands include Jims, S&S Cycle, Motion Pro, TMV and Eastern Motorcycle Parts. Related categories are Crankshafts, Connecting Rods & Parts and Engine Bearings.
FAQs on flywheels and flywheel parts
What does stroke mean in a flywheel assembly listing?
Stroke is the distance the piston travels between the top and bottom of its movement, set by the crank pin offset in the flywheels. A longer stroke increases displacement, but the cylinders and pistons must be chosen to match.
Do I need a puller to remove a flywheel or rotor?
Yes, in most cases. The puller threads into the rotor and pushes against the crankshaft end, so the rotor comes off without prying or hammering. Using the wrong tool can damage the crank or the rotor.
Why does a flywheel puller list a thread size such as M28 x 1?
The numbers are the thread diameter and pitch in millimeters. The puller thread has to match the internal thread in the rotor, and the thread is listed as right hand or left hand. Check the manual for your engine.
Can I fit a bigger-stroke flywheel assembly to my stock engine?
Not as a simple swap. A longer stroke raises the displacement and changes clearances, so the cylinders, pistons and other parts must be matched to it. Follow the assembly maker's instructions or use an experienced engine builder for the job.
What does adding flywheel weight do on a dirt bike?
More rotating mass smooths the way the engine picks up power and can help with traction, but it also slows how quickly the engine revs. Use only the weights listed for your model, and check the maker's notes before fitting one.
