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How to Lap a Cylinder

Lapping a cylinder head involves grinding the part so that the surface where it makes contact with the engine cylinder is even. Sometimes, cylinder heads warp due to the way in which they are tightened and the temperature of engine use. Left uncorrected, air and fuel can leak through the warps. Lapping fixes this problem and keeps the part working in proper order.

Instructions

Car Cylinder Head Lapping

1

Remove the cylinder head from the car engine. Clean the cylinder head using a rag and solvent. Remove any old carbon or grease on the head surface. Mix a lather of silicone carbide grit with a little bit of water. Stop mixing when it becomes a paste. Apply a lather of the grit by covering the mating surface of the cylinder head using your finger. The mating surface presses against the cylinder when the cylinder head is bolted to the engine.

2

Place the cylinder against the cylinder head, and begin to twist at a slow pace. Twist back and forth, so that the cylinder head surface grinds smoothly from multiple directions. Remove the cylinder after a few minutes of twisting.

3

Examine the cylinder head for any low spots or areas that you have not ground to a smooth surface. Continue the twisting until finished. Wash the cylinder and cylinder head with water to remove all the grit and grindings. Dry the parts off with a clean towel to avoid oxidation. Use the parts as necessary.

Motorcycle Cylinder Head Lapping

4

Disassemble the motorcycle or scooter cylinder head. Clean it with a rag and solvent, so that there is no leftover oil or carbon on the cylinder head.

5

Take a sheet of very fine grit sandpaper, and tape it to a two-by-two foot sheet of flat plastic board. Hold the cylinder head in one hand, and lay it flat on the sandpaper.

6

Begin slowly but firmly to move the cylinder head in a figure eight, circular motion across the sandpaper -- this motion facilitates even grinding. Move in a figure eight across the board, so that the head surface grinds clockwise and counterclockwise. Do not sand or lean in one direction only. Continue the figure eight motion until you have completed five figure eight motions or cycles.

7

Lift the cylinder head, and examine the surface that mates with the cylinder. Continue the figure eight grinding until the surface is completely sanded at every point with no low spots. Wash off the cylinder with water, and dry. Use as needed.

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