I am building a 450-500 hp honda civic with a d16y8 head, i purchased brand new valves , and i was wondering how do I get these valves to seat and seal the chamber for combustion? Is lapping the valves effective enough to ensure the head will hold compression or do I have to go the extra mile and get some precision machine work done??

2 Answers 2


If you lap them in and get a proper seal then machining is not needed.

If the new valves are supplied without the final surfaces angled correctly i.e. as a “blank”, then they need machining.

  • Have a shop grind the seats and the valve faces for proper fit. You'll never get a good seal using new valves and old seats just with lapping compound.
    – user9181
    Apr 24, 2020 at 18:40
  • 1
    @user9181 I had, perhaps erroneously, assumed that the head was new and the OP does state clearly that the valves are new...
    – Solar Mike
    Apr 24, 2020 at 18:44

Since it is high performance, I would let a reputable automotive machine shop do a 3 angle valve job. Better flow and performance and everything gets checked, including checking for cracks in the aluminum head. Have it surfaced for a good head gasket seal also.

Find a machine shop that has experience in performance work.

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