Valves, valve seats and guides — inspection and repair (Mitsubishi Colt 4)

Check the valve plates (especially the exhaust ones) to see if they are burnt or have pitting corrosion. At the same time, inspect the seats. If the damage is minor, you can grind the seats and valves together using first a coarse and then a finer grinding paste. You can pre-clean off any deposits with sandpaper.

If the pitting corrosion is severe, the seats can be reground to fit new valves. If the seats are very badly damaged, the seat inserts must be treated or replaced. However, valves are damaged much more often than seats. That is why they are reground to fit the seats.

Install the valve into the guide bushing and press the valve disc against the seat.

Measure the dimension from the seating surface of the valve spring seat (plate) to the end of the valve stem

If the measured value exceeds the required value, replace the valve seat. To do this:

Drill out the valve seat, leaving the seat walls 0.5-1.0 mm thick.

Press out the valve seat.
Treat the socket to accept a repair size seat.

After heating the cylinder head to 250°C or cooling the seats, press the seats into the cylinder head.
Adjust the valve seat dimensions to the required size.