The Honda XR 250 is a single-cylinder, four-stroke motorcycle built for off-road use. Because this recreational vehicle is most likely put through rigorous riding and extreme conditions, it is important to keep the engine and vital parts serviced frequently. If you notice your XR250 is overheating very quickly or performance is down from normal use, it is best to check the head gasket for any leaks. Replacing this head gasket can be quite the task, but with a little patience and the right tools, you should be able to tackle this process in an afternoon.
Unscrew the bolts that hold the fuel tank in place, and lift this part off of the XR 250. Remove the seat of your bike, as well, as most of the parts you will need to access for this procedure are located underneath the seat and tank.
Unscrew the bolt that holds the negative terminal to the battery and disconnect completely. Set this wire aside so that it does not ground itself to any metal part. Remove the spark plug cap, then use your spark plug wrench to remove the spark plug inside this port.
Remove all valve cover bolts of the engine, turning counter-clockwise 1/2 turn each time. Continue doing this until all valve cover bolts have been successfully removed. Now, remove the cam chain tensioner, located at the rear of the cylinder heads. Remove the cam sprocket and secure this part so that it does not fall down into the engine.
Unscrew all of the bolts, one quarter-turn at a time, that hold the cylinder head to the engine. Lift the cylinder head off of the engine slowly and set aside for later use. Remove the old cylinder head gaskets with your hands. If necessary, pry both of these gaskets off of the engine block with a flathead screwdriver. Dispose of this part properly, as you will not need it any longer.
Apply gasket removal solvent to a linen cloth and remove all of the excess build-up that has formed on the engine over the years. If necessary, use a plastic scraper to fully remove all of the harsh material.
Apply a thin layer of gasket sealant to both sides of the new gaskets. Determine which side of the new gaskets should be face down and position into place. The holes of the cylinder ports should align with the two new head gaskets that you have just laid down. Position the old cylinder head and install all bolts to secure into place. Torque these bolts, one full turn each at a time, to 29 foot-pounds of pressure.
Reinstall all of the wiring and parts that were removed to access the cylinder head. Make sure everything installs exactly as it was removed. Connect the negative terminal to the engine's battery. Replace the seat and tank when you are finished with all of the engine part installations.
Wear gloves and protective eyewear during engine maintenance. Let the engine cool before performing and engine maintenance. Draw out diagrams of any wires or parts you remove if you do not think you will remember the exact layout.