When the four-stroke CRF450R hit the tracks in early 2002, sales of the two-stroke CR250R plummeted. Most of the slump can be blamed on the four-stroke's phenomenal motor, but we'd be remiss if we overlooked the less-than-stellar powerplant wedged between the aluminum spars of the '02-'04 250 frame. With the decline in CR250R customers and all the attention the bike's bigger cousin was receiving, we asked Rick Peterson of RPM's in Covina, California, to build us a big-bore CR280 project.
RPM's needs the complete engine for these mods. The kit costs $2200, which includes all labor and parts. First, the company splits the cases (and phones the customer with a list of worn parts that might need replacing). The cylinder is then bored out 2mm, ported, decked and plated with nikasil. This is the same plating that many of the factory teams have Peterson put on their works cylinders. The crank is pressed apart, and the crankpin holes are machined 2mm farther from the center of the crank. These larger holes are then sleeved down with hardened steel collars so the stock rod kit can be used. RPM's balances the crank by drilling holes opposite the crankpin and pressing in tungsten. The crank gains a few ounces, but the reduction in vibration is amazing. "A balanced CR280 is smoother than the stock CR250R," Peterson claims. Finally, the engine is reassembled, and the head is chambered to run the octane you specify on your order form.
If the lower end has a lot of time on it, RPM's suggests replacing the crank with a Wiseco H101 unit, which retails for $217. This was standard equipment on '92-'01 CR250Rs and is much lighter than the '02-'04 piece. The lighter crank gives more of a snappier feel than the electric smooth feeling of the newer CR.
We rode the RPM's CR280 at a secret fast, choppy sand track here in SoCal. The minute we took off on it we could tell this CR has a very powerful mid to top-end. However, it still had the CR250R's smooth-feeling bottom-end, which is not a bad thing, as it makes the bike easy to ride. As you roll the throttle on more, you feel the pull of the 280. When shifting from third to fourth gear, the bike could be left in each gear longer than the stock 250, which was very lethargic compared with this motor. On top, the bike actually revved higher also. On long, fast, choppy straights where the wheel comes off the ground and overrev is noticeable, the CR280 is clean and revs much longer than any other CR we've ridden to date. That is important in outdoor racing. You want a motor that is broad but also can be revved. The CR280 delivers.
This bike would also be great for the vet racer who does not want the heavy feel of the CRF450R but still wants its tractability and smoothness. The CR280 is easy to ride yet can be ridden aggressively. It keeps the nice, smooth feel but actually has a powerband now. For the die-hard two-stroke fan, the CR280 is a winner!