The grinding on the seats is very important as it corrects and trues the contact patch between the valve and the seat. A correct job will have a seat contact patch about the width of a dime on the intake and a little bit wider on the exhaust. Also the intake contacts the face of the valve towards the outer edge with the exhausts square in the middle. You check this by taking the heads and valves clean and spray a graphite spary on the valve and slam it against the seat, the contact will remove the graphite revealing the seat contact patch on the valve. Now compare the freshly done heads to a set of heads that has alot of time on them and you will see a major difference. Also, with the valves (mark the valves and dont mix them up) and springs installed in both sets of heads, pour solvent in the ports and look for leakage at the valves and seats. Worn heads will leak considerably and this is part of the reason behind poor leakdown test results. Disclaimer: I hope I remembered all of this correctly as I did this work directly out of highschool until I decided it would never pay very well and moved on, that was back in the 80's and my memory treats me like a red-headed step child sometimes. Anyone have more recent information?
|