Damaged valve seats can be re-machined using a jig and seat cutting machine. The following shows recutting of valve seats on a 270mm bore medium speed 4 stroke cylinder head. It is considered superior to grinding the seats with a wheel as it is not affected by vibration to the same degree, which gives problems with chattering on the surface.

The cylinder head is mounted upside down on a table manufactured to carry out the task. The table in the photo was built by ships staff.

The valve cutting machine locates on a spindle which is fitted into the valve guide. It goes without saying that the spindle must be a close fit in the guide for alignment purposes.

The cutter is lined up with the valve seat. and a small cut is adjusted using a feed screw on the top of the machine.

The machine is connected to an electrical supply. When switched on, the cutting head revolves and the tool automatically feeds across the valve seat at the correct angle.

The process is repeated with small cuts until a good finish is obtained.