Q: If I have a 100% completely new cylinder head and engine valves, do they still need to be ground together or can I install them as is?

A: It depends.

Most of the time, you buy a new cylinder head already assembled with the valves, guides, seals, springs, etc already installed, and the valves should be perfectly matched to the seats.

But sometimes you buy a bare head, expecting to install most or all of the valves, springs, and so forth from the old head, in which case you should make very sure the valves and seats fit together properly.

And SOMETIMES you will buy the components separately, from different companies, and different manufacturers. This is common when building high performance engines. In this case the valves and seats will PROBABLY be matched properly, but the only way to be sure is to check very carefully, by running a pressure test.

This is a routine procedure performed by all competent automotive machine shops when servicing cylinder heads, and you can take your head in and have it tested. The cost of this test is about forty bucks in my area. It may cost twice that or more in some places, and it may cost more depending on the kind of engine the head goes on.

Work on Mercedes or Beemers means the price will automatically cost a lot more than the same work done on a Chevy or Ford, lol.