Diesel Engine Troubleshooting

Archive for the ‘Seat Replacement’ tag

Diesel Engines Cylinder Head Seat Replacement

without comments

Valve seat inserts are pressed into recesses machined into the head. (Some very early engines used spigoted inserts with mixed results.) Seats must be replaced when severely burned, cracked, loose, or as a means of obtaining the correct valve protrusion. Many shops routinely replace seats during an overhaul for the insurance value.

Seats in iron heads are customarily driven out with a punch inserted through the ports, although more elegant tools are available (Fig. 7-33); seats in aluminum heads should be cut out to prevent damage to the recess (Fig. 7-34).

While new seats can be installed in the original counterbores, it is good practice to machine the bores to the next oversize. Replacement seats for most engines are available in 0.010-, 0.015-, 0.020-, and 0.030-in. oversizes. Material determines the fit: iron seats in iron heads require about 0.005-in. interference fit; Stellite expands less with heat, and seats made of this material should be set up a little tighter; seats in aluminum require something on the order of 0.008-in. interference.

Seat concentricity should be checked with a dial indicator mounted in a fixture that pilots on the valve guide. Often the technician finds it necessary to restore concentricity by lightly grinding the seat.

Written by Ed

February 18th, 2011 at 2:23 am

Posted in Cylinder Heads

Tagged with