Motorcycle head gaskets are designed to endure heat generated by combustion in the cylinder head for thousand of miles. Head gaskets fail in progressive stages each time the engine overheats and exceeds the limits of the gasket. Your XR250 Honda has twin cylinders and a single head gasket that installs atop the cylinder jacket. Removing the head and replacing the gasket requires patience and mechanical aptitude on your part. Looking at the engine, notice the cylinder head is below the gas tank and the seat extends over the tank. Remove the seat and gas tank to replace a head gasket on a Honda XR250 motorcycle.
Removing the Cylinder Head
1. Disconnect the negative battery cable from the battery. Remove the spark plug wire caps from both plugs. Remove the spark plugs. Remove the cam cover bolts and lift the cover off of the cylinder head.
2. Remove the timing cover at the side of the engine crankcase. Remove the timing chain inspection cover, located at the back of the cylinder jacket, just above the crankcase.
3. Take a position where you can observe the ignition-timing flywheel and operate the kick starter by hand. Rotate the engine using the kick starter and align the timing marks on the flywheel with the timing indicator needle. It’s important to have the timing in this position when reattaching the valve cam chain.
4. Loosen the cam chain tension bolt located inside of the inspection cover. Look inside the top of the head where the cam cover was removed. Locate and remove the clip on the front cam bearing cap and remove the cap. Slide the bearing to one side and lower the cam enough to lift the cam chain off of the cam sprocket.
5. Allow the cam chain to rest below the cam. Put the cam back in place in the head. Slide the bearing to its original position against the cam sprocket. Replace the bearing cap and secure it with the clip. This process is repeated in reverse when reattaching the cam chain over the sprocket.
6. Loosen and remove the cylinder head bolts. Tap the sides of the head with a rubber mallet to unseat the head gasket. Lift the head off of the cylinders and place it on a workbench.
7. Scrape the old gasket off of the head with a putty knife. Buff the underside of the head using an electric drill with a fine wire wheel attachment. Stuff shop rags into the top of each cylinder on the engine. Buff the top of the cylinders. Carefully remove the rags and avoid dropping residue inside the cylinders.
Head Gasket and Reassembly
1. Identify the top and bottom sides of the new head gasket by marks or letters. Position the gasket on the cylinders with the top side up. Align the holes in the gasket with the bolt holes on the cylinders. Place the cylinder head atop the gasket and onto the cylinders, taking care not to move the gasket out of alignment.
2. Refer to the torque specifications in your repair manual. Typical torque is 29-ft lbs for Honda 250cc cylinder head bolts. Tighten and torque the head bolts in a crisscross pattern to avoid over-compressing one edge of the head gasket.
3. Remove the clip on the cam bearing cap, slide the bearing to one side and lower the cam. Lift the cam chain onto the sprocket. Put the cam back in place. Slide the bearing into place against the sprocket. Replace the bearing cap and clip.
4. Refer to the repair manual for cam chain adjustment procedures. Adjust the chain tension and replace the inspection cover at the back of the cylinder jacket. Reattach the timing cover at the side of the engine crankcase.
5. Reattach the cam cover onto the head. Reinstall the spark plugs and attach the plug wires to each plug. Reconnect the negative battery cable to the battery. Reattach the seat the gas tank.
Items you will need
- Metric tools
- Spark plug wrench
- Rubber mallet
- Shop rags
- Putty knife
- Electric drill
- Fine wire wheel attachment
- Head gasket
- Torque wrench
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