Press room

Athena presents the new Extreme Big Bore cylinder kits for Offroad

25 May 2023

Alonte (VI), May 2023

Athena – a leader in the market of high-performance motorcycle, scooter and moped spare parts for 50 years – presents the brand new Extreme Big Bore cylinder kits measuring Ø85mm, for offroad applications for Honda and Yamaha 250cc.

The Athena R&D Department succeeded in designing and developing a solution that filled a market gap: a Cylinder kit with extreme increased bore that allows an unprecedented increase in power, bringing the displacements of Yamaha and Honda bikes up to 304cc and 288cc, respectively. The kit can be installed without making any modifications to the motorcycle crankcase.

In fact, the entire Kit guarantees maximum performance, better delivery, more torque at low and medium revs, better reactivity and at the same time a reliability equal to the original parts, thanks to all the technical solutions resulting from the challenge won by the Athena R&D team. All this is combined with the proverbial good handling of a 250cc Offroad for a simply exceptional driving experience.

Athena's Technical Department internally manages the entire development and approval process for the cylinder kits. First, the team works to design together all the elements of the kit. They are first tested and validated by the company test facility technicians and then directly on the track by the riders.

The result is a combination of engine components that ensure maximum synergy between them.

The cylinder

The winning feature of this revolutionary kit is the cylinder resulting from the union of two different materials, with particular attention to the design of the cylinder wall.

The cylinder with extreme increased bore Ø 85mm is in fact made of aluminum alloy with a high silicon content, with a steel cylinder liner. This cylinder liner is placed directly into the mold through an innovative co-fusion production process. This internally designed and tested method allows efficient mechanical gripping, and ensures perfect union and reliability over time.

Furthermore, the cylinder liner is finished with a galvanic treatment and a nickel-silicon coating developed by the Athena R&D department, to obtain maximum smoothness and optimal resistance to wear even under high performance conditions.

Piston kit

The forged aluminum alloy piston is a guarantee of resistance and lightness. Additionally, machining with the latest generation CNC machines ensures perfect geometries and reduced tolerances.

The lower structure has a fully open boxed bridged design to combine greater resistence to fatigue, lightness and a better cooling of the piston crown.

The geometry of the piston crown also optimizes the compression ratio to guarantee greater driving elasticity and reliability over time.

The piston pin was specifically designed for this type of extreme application. It is biconical and made in aeronautical steel alloy and the segments included were made in Japan.

Gaskets kit

The gaskets included in the kit, developed by Athena technicians, include a cylinder head gasket and a cylinder base gasket. These were specifically designed for the new aluminum cylinder with steel liner, to guarantee maximum seal even under the most extreme stresses.

The Athena Big Bore Extreme Cylinder kits are available to the public at this suggested price:

Kit Big Bore Extreme Honda 250cc: 606,27 €

HONDA CRF R 250 cc 2018/2023

HONDA CRF RX 250 cc 2019/2023

Kit Big Bore Extreme Yamaha 250cc: 594,18

YAMAHA YZ F 250 cc 2019/2023

YAMAHA WR F 250 cc 2020/2023


To find out more, visit