Cylinder Works - YZ250 Complete Cylinder Kit

The Cylinder Works complete cylinder kit is a ready-to-install top-end replacement for the Yamaha YZ250 two-stroke. Rather than sending a worn, scored or flaking cylinder away for re-plating and waiting on the turnaround, you fit a brand-new standard-bore cylinder that bolts straight on and looks near-identical to the original Yamaha item.

Everything needed for the rebuild comes in the one box, including a matched Vertex piston, cylinder head, top-end gaskets, wrist pin bearing and a power valve kit. The matched piston-to-bore pairing is what gives the kit its consistent ring seal, quieter running and longer service life.

It suits riders and workshops rebuilding a tired YZ250 top end, and anyone who wants a fresh, known-good cylinder rather than a reconditioned one. Please confirm the part suits your machine's model year before ordering.

• Complete bolt-on top-end kit for the Yamaha YZ250 two-stroke
• Brand-new cylinder — no re-plating or cylinder repair work required
• Standard bore, 66.400 mm cylinder diameter
• Matched Vertex piston supplied with the cylinder for consistent fit and ring seal
• Standard compression ratio, so no fuel or tuning changes are implied by the kit
• Cylinder styling and fitment closely mirror the OEM component
• Includes cylinder head, top-end gasket kit, wrist pin bearing and power valve kit
• Suits 250 cc two-stroke applications

• Cylinder
• Cylinder head
• Piston kit
• Top end gasket kit
• Wrist pin bearing
• Power valve kit

Confirm the kit matches your YZ250's model year and engine configuration before removing the old top end — power valve and cylinder designs changed across generations.
Carry out the fit-up and all torque figures, tightening sequences and squish/clearance checks to the Yamaha service manual for your model; do not rely on generic values.
Check piston ring end gap in the new bore before assembly, and confirm the wrist pin bearing and circlips are seated correctly with circlip openings positioned as the manual specifies.
Use the supplied top-end gaskets and a fresh base gasket set-up as specified; avoid sealants on gasket faces unless the service manual calls for them.
The cylinder bore is plated and ready to run — do not hone, deglaze, bead-blast or machine it, and never use abrasives or wire brushes inside the bore.
Clean the new components with a lint-free cloth and clean solvent before assembly, then coat the bore, piston skirt and wrist pin bearing with two-stroke oil prior to first start.
Run a proper break-in: several gentle heat cycles with varied light-to-moderate throttle, allowing the engine to cool between cycles, before any sustained hard riding.
Use fresh fuel and a quality two-stroke oil at the premix ratio specified by Yamaha for your machine; lean or stale mixtures are the fastest way to damage a new piston and bore.
Fit a clean, correctly oiled air filter and inspect the intake tract for leaks or dirt ingress — grit passing the filter will score the new bore.
Keep the power valve components clean and free of carbon build-up, and inspect them at the service intervals in your manual along with the exhaust system.
Inspect the piston, rings and bore at the top-end intervals given in the Yamaha service manual, and replace wear items rather than running them out.
Store the kit in its packaging in a dry place until installation, and keep the bore lightly oiled if the engine will sit unused for an extended period.