YAMAHA PISTON 0.25 688-11635-03 REC688-11635-03K

Function and technical context

The piston and its rings constitute the heart of the combustion system in Yamaha four-stroke engines. The piston moves inside the cylinder, transforming the thermal energy of the fuel explosion into mechanical movement, while the rings guarantee the tightness of the combustion chamber and control the passage of lubricating oil to the crankcase. This +0.25 mm oversize kit is installed when the cylinder has suffered normal wear and requires rectification, allowing the correct adjustment tolerances to be maintained. Precision in the assembly of these components is essential to preserve engine compression and avoid gas leaks that would compromise power and fuel consumption.

When to replace this part?

Piston and ring wear gradually manifests itself through progressive loss of power, increased oil consumption, bluish smoke in the exhaust and difficulties in cold starting. After checking the cylinder and detecting excessive clearance between piston and wall, rectification of the cylinder to +0.25 mm requires installing this oversize kit to restore the correct operating clearances. The preventive replacement of this assembly during major maintenance avoids damage to the cylinders and costly rectification processes involving greater oversizes that would limit the useful life of the engine block.

Equivalent manufacturer part numbers