Yamaha Cylinder works YZ250 big bore 295cc 72mm Phathead cylinder head kit 1999-2026

Yamaha Cylinder works 295cc big bore 72mm Phathead cylinder head kit 1999-2026

We also make a kit for the Athena big bore kit.  This does not fit the Athena.

Chamber selection:

CW295 - 72mm 91+ octane 

CW296 - 72mm 100+octane 

CW297 72mm 105+ octane

Phathead Kits include a head shell with one combustion chamber, cylinder head nuts, copper washers, some stickers for your bike and tool box and installation instructions..

Phathead cylinder heads are made of 6061 T6 billet aluminum.  The material is stronger and transfers heat better than cast aluminum.  The two piece design allows an increase in coolant flow as well as surface area which improves cooling for better consistency and performance.   

One of the main benefits of the product is the replaceable combustion chamber which are available in a range of compression options.

Suggestions : Swap chambers to adjust performance for a variety of riding conditions and track types or keep a spare in case of engine failure.