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.