Valve Seat Cutting
Here’s what I know to be fact, and how I do mine.
A 3 angle valve job includes a 45 degree cut to match the 45 of the valve. Above the 45 is a 30 degree lead in cut(sometimes Kawasaki uses a 32 here), and below the 45 is a 60 degree cut leading into the port. NOW, I say 5 angle valve jobs are BOGUS. In order to do that you would need a 75 degree cut under the 60, (I WHOLE HEARTEDLY AGREE WITH THIS). Then a 15 degree cut above the 30. This is NOT possible on almost all of late model Kawasakis. The reason is they put such a narrow 30, there’s no metal or room left to add the 15. In most cases, the 30 is hardly existent.
SO I say a 4 angle cut is the ticket, 30,45,60,75. Now if you put your head on a serdi 5 angle machine, it can reprofile the entire seat to add all (5) angles, but to do that sinks the 45 into the head, increasing combustion chamber volume and lowering compression.
Here’s how I do mine, and I know it works. First of all I don’t use a 45 seat. I use a 46 degree seat. This causes a interference fit between the seat and valve resulting in sealing at the outer edge of the valve where you want it.
I put the 75 degree cut below the 60. I use the 60 bottom narrowing cutter to trim the bottom of the 45(46) to 1mm in width on intake 1.5 mm on exhaust. The exhaust seat needs to be a little wider for increased cooling.
This SHIT flat flows. Now I cut all my seats by hand using special cutters made by Neway Manufacturing. THESE ARE NOT GRINDING STONES, like shown in the Kaw manual and sold by most tool dealers. They Neway, have a web site. I will see if I can find it and post it. Now, when you take your head to a shop nowadays, they never tell you what your getting exactly, they just say “MULTI ANGLE”, and a 4 valve job is what you get.
If someone tells you they are using Neway cutters and are putting a 75 degree bottom cut, you are getting the best valve job in my opinion. I would put this up against anything a machine can do.
Epoxied up 91-95 ZX7 heads, as well as 94-97 9 heads, if done correctly really flow some air. These heads had ports that were to big. So making them smaller increases the velocity and more flow. Probably why Kaw put smaller ports on the 96-00 7s.
As far as milling heads go, I don’t think you can remove more than .003 inch of a 91-95 7 head. THATS NOT MUCH, after that you start cutting into the seats, sounds BOGUS to me.
Oh, one other thing, seats cut with NEWAY, do not have to be lapped afterwards. All other methods require lapping.
Check out this site, it gives you some idea what the seat cutters look like. If I was going to get a valve job, I would shop around till I found a shop that uses Neway, and then tell them to put the 4th or 75 degree bottom cut on.