2005 Honda CR250R

2005 Honda CR250R: Honda's Major Two-Stroke Refinement

The 2005 Honda CR250R was more than a graphics-and-jetting update. Although it retained the third-generation aluminium-frame platform introduced earlier in the decade, Honda substantially reworked the 249 cc two-stroke engine, intake system, transmission and chassis setup. The objective was clear: improve the low-to-midrange response that had been a weakness of the earlier case-reed CR250R while retaining the strong top-end performance expected from Honda's premier 250 motocrosser.

Much of the development focused inside the engine. Honda revised the cylinder port shape and port timing, reshaped the combustion chamber and piston crown, and replaced the previous two flat piston rings with a single half-keystone ring. The lighter ring arrangement reduced reciprocating mass and friction. The RC exhaust-valve installation was also redesigned to improve sealing, helping the engine produce cleaner response at lower rpm without sacrificing its high-rpm performance.

The intake system received equally serious attention. Honda changed from an eight-petal reed assembly to a six-petal design with sub-reeds, revised the intake opening and reshaped the crankcase intake passage. Fuel continued to come from a 38 mm Mikuni TMX carburettor with throttle-position sensing, so correct jetting remained important. Owners working on ageing examples can use the MXOwners carburettor reference when investigating replacement or repair options.

Durability and shifting were also targeted. Honda increased crankcase rigidity around the crankshaft, heat-treated the connecting rod and used a special steel alloy for the piston pin. Changes within the five-speed transmission, including treatment of the shift-fork shaft, were intended to improve shift feel. For owners rebuilding a twenty-year-old CR250R today, identifying the correct year-specific components is important because apparently similar parts are not always interchangeable; the MXOwners parts finder can help with that process.

The chassis was refined rather than replaced. Honda altered the front axle offset to improve cornering and steering control, while changes to the swingarm, rear hub and chain-guide components reduced unsprung weight. The 47 mm Showa twin-chamber fork and Pro-Link Showa rear shock remained fully adjustable competition components. Fork servicing is particularly sensitive to correct oil volume, and the MXOwners fork oil reference is useful when checking suspension information before a rebuild.

For owners, one of the most important details is that the 2005 CR250R remained a conventional premix two-stroke. Honda specified a 32:1 petrol-to-oil ratio using its HP2 two-stroke oil or an equivalent quality lubricant. Unlike a four-stroke CRF, the gearbox has its own separate oil supply, with approximately 0.65 litres required after a normal drain. Keeping the foam air filter properly cleaned and oiled is equally important, because dirt entering a two-stroke engine can quickly damage the piston, rings and cylinder.

Historically, the 2005 model represents Honda's continuing effort to perfect the CR250R late in the Japanese 250 two-stroke development era. Four-stroke motocross machines were rapidly taking over top-level competition, but Honda was still putting substantial engineering effort into the CR. The 2005 machine therefore stands as one of the most developed versions of the aluminium-framed, case-reed CR250R and remains an interesting model for riders and restorers who want one of Honda's final generations of open-class two-stroke motocross machinery.