Tuesday, 14 April 2015

How To Replace Valve Seat Inserts In Cylinder Heads?

Valve seat inserts replacement is one of the initial tasks that is often required when rebuilding cast iron or aluminum heads with damaged, cracked, or badly worn seats. If the cylinder head is made from CI material with integral seats, it has to be machined to replace the seat, whereas if the cylinder head is made from aluminum, it has to machine to accept an oversize seat in case of loose, damaged, or deformed bore. In any manner, engineer has to determine the interference amount that is required for the new seat prior cutting the head. Moreover, he needs to decide the seat type for installation.

Do You Know Why Your Valve Seats Breakdown?

There are numerous reasons that support non integral valve seats failure. Most of the seats for which replacement option is left are replaced as they are too much damaged, cracked, or worn. This is due to thermal stress, mechanical stress, or thermal shock.

Slight amount of valve shortage leads to normal to high mileage wear. It can also occur when dry fuel like natural gas is used inside the engine that does not have hard seats. Shortage of valve occurs when the microscopic welds form between the seat and valve face and the temperature of the seats increases. As many times the valve opens, little metal chunks are torn away and exhausted. After time, the seat worn out and valve gradually sinks deep inside the cylinder head. And the lash present in the valvetrain closes up and keeps valves away from seating, which results in overheating and burning of valve. It also loses the compression and results in bad valve.

How To Perform Valve Seat Removal Process?

The techniques that majority of valve seat inserts manufacturers and repairing centers use are:
  • Few use bake ovens or an open flame thermal cleaning system to remove the dirt and grease from the heads and loose the seats in single step. Using bake oven, the cylinder heads are loaded with downward mounted seats and heated to 450 degree Fahrenheit. In case the fall out of seats does not occur, these can be expelled even when the head is hot.

  • Seats can also be removed if the seats' underside is easy to access via valve ports, using a long punch to pull them out. But this step needs more care and expert assistance.

  • Some of them are also using specialty tools for pulling out the seats.


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