To fulfill basic performance requirements as an on/off-road model while setting higher targets for environmental performance, the development team came up with a roller rocker arm design for the valve system. The extremely compact layout allows a low-fiction valve system to be achieved with a small cylinder head.
Combustion efficiency has been enhanced through the selection of an iridium spark plug that is highly ignitable even with lean mixture and lasts about four times as long as a regular plug. Coupled with the optimization of fuel injection through the use of PGM-FI, its fuel efficiency has moved up to rank among the top of the on/off-road category.
To reduce the friction of the piston's reciprocating portion, the CRF250L employs an offset cylinder (offset 4 mm to the exhaust side), and the piston incorporates thick streaks and molybdenum coating, which facilitate lubrication by engine oil.
Conceptual diagram of offset cylinder
Liquid-cooled 4-stroke DOHC single-cylinder engine