Race Engine Forum UK

Hello Guy and everyone.
It is very pleasent for me to write here.
This car works on bike carbs from Kawasaki Ninja zx9r.
Now I am trying to modificate the head of this engine.
I'd like to ask your opinion about my work.
Is it necessary to cut the seats into 3 angles? And what can it give?
Thanks,
Yours very sincerely,
Zhenya.

I have done similar heads.

I recommend a very small diameter top cut (or grind) to true up the top section of the seat inserts first, this is important because if it's not concentric to the valve axis and properly perpendicular to it the contact face can be elliptical and you can lose the alpped seat altogether in places. I suggest 15 deg or better 20 deg. I know there isn't much room for the cutter, I think I used a Neway 20 deg set just slightly bigger than seat diameter. Always start on the seat insert which is in the worst condition as that will then set the valve tip height for all of them.

Other angles inlet: 45deg x 2mm x 75deg - fully blended into throat at the bottom.

Give the OE inlet valves (only) a 25 deg back grind leaving a contact face the same width as the seat insert one.

Exhaust: top cut as inlet the 45 x 2mm x 70 deg again fully blended into throat.

I suggest you do the inlet valve back-grind and lap in/ex valves before doing the final 75 & 70 deg throat grind as you can then grind right up to the contact face on the inlet (which, if you've done the back grind right will be 2mm wide); on the ex side you can use the 70 throat grind to reduce the width of the ex contact face down to 1.5-1.75mm


Hope this helps some,

G

Remember that seat mods drop the valve deeper into the head - be careful that you can do the valve clearances. Of course you can grind the valve tips to reduce the tip height.

Thanks Guy for your advice. I try to do as you said.