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Price: $400.00

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The WR250R is not exactly an enduro model and it's not a streetbike. Its partner, the supermoto-inspired WR250X, is for riders who spend more time on pavement than off it.

When we first got a chance to ride the WR250 we had a lot of fun with it. On the street it is mild mannered and fun. Once we took the WR250R on anything tougher than a dirt road or pushed the WR250X on the pavement we immediately notice; both models are lacking bottom end grunt. The motor makes power but needs to be rev'ed out in order to find it. We set to work coming up with the perfect blend of bottom end increase without hurting the enjoyable characteristics of the stock motor. A lot of thought went into how big do we go? Countless combinations were tried. In the end we decided to stick with a 280 kit, the reason for this was simple: Doing a 290 kit made the piston too heavy. Keeping the kit a 280 gave us a piston weight that is 8 grams heavier than stock. If we had gone with a 290 the piston came in at 28 grams heavier which you could feel in the higher RPM's. This gave the motor a buzzy feeling at higher RPMs. By staying with a 280 kit we minimized any increase in vibration, reciprocating mass is minimal and engine longevity is ensured.

We designed the Thumper Racing WR250R/X big bore kit using a ductile iron sleeve instead of nikasil. You may ask why ductile? For strength and longevity, over boring the stock cylinder is not an option for us. The cylinder walls become too thin with a straight overbore and boring the cases to fit a larger aluminum cylinder is not cost effective. Ductile has very similar wear properties as Nikasil, but the tensile strength is 5 times higher, which resists deforming and warping 5x better than aluminum. The WR250R/X sleeves are also designed with our patented Cool Flow. The Cool Flow design for the WR250R/X has 15% more surface to water contact area than the stock cylinder casting, which promotes better heat transfer for improved cooling.

Parts only: The WR250R/X big bore parts only kit includes: Ductile iron sleeve, moly coated piston kit, top end gasket set, and instructions for sleeve installation. Sleeve install and hone should be completed by an experienced machinist.  NOTE:  This option requires you to have the sleeve installed in your cylinder.
Installed in your cylinder: The WR250R/X big bore kit includes: Ductile iron sleeve installed in your cylinder, moly coated piston kit and top end gasket set.  Cylinder turnaround time in most cases is 1-2 days.  NOTE: This option requires you to send in your cylinder for resleeving.
Installed in your motor: The WR250R/X big bore kit installed in your motor includes: Ductile iron sleeve installed in your cylinder, moly coated piston kit, top end gasket set and all labor to install the kit in your motor out of the bike. For motor in bike please call us at 775-309-4956.
Note: This kit requires a fuel controller. If you already have a controller and we have a map available (we have maps for DynoJet Power Commanders) for it we will program it for free. If you need a controller there is no additional charge for programming and installation of the controller other than the cost of the controller itself. Keep in mind we offer a 15% discount on either with the purchase of a kit as our way of saying thanks.

Option 1: We send you the parts - Price: $400
Option 2: You send us the topend to install the kit - Price: $555
Option 3: You send us the motor to install the kit - Price: $635 


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