Modern premium high speed motorcycle engines represent a particularly demanding environment for component design. The severe nature of the internal thermal and mechanical loads in such engines has traditionally necessitated extensive development testing in order to ensure that design targets are met. In order to meet the increasing commercial pressures for improved product refinement and durability coupled with reduced development timescales, the effective application of a modern analysis techniques should be regarded as an essential part of the design phase.
This paper describes the approach used to develop the design of a lightweight slipper construction piston, pin and connecting rod for use in a new family of motorcycle engines. A finite element model of the piston was used to assess the effectiveness of various piston cooling regimes. Development of the piston skirt ovality profile for minimum clearance (and hence low noise) was also undertaken on the model, with reference to the results of an FE analysis of liner distortion and calculations of skirt stiffness distribution.
A lightweight, internally tapered, fully floating, bushless gudgeon pin was designed using a non-linear system model of the connecting rod small end, pin and piston allowing for the clearances between each component.
The connecting rod was designed using an FE model incorporating big end wrap round. An iterative approach was applied whereby material was redistributed on the basis of local fatigue safety factors. The final 3D surface geometry was transferred to a CAD system for detailing prior to procurement.
The approach described enabled a competitive lightweight design of piston, pin and connecting rod to be produced on a “right first time” basis as a part of a single stage design and development programme. Sufficient confidence was placed in the approach for production rather than prototype tooling to be procured on the basis of the analytical results. Subsequent durability testing was carried out on entirely production parts.