valve seat blending and unshrouding ?'s

[nategdizzle]

ok now that it is warm again i have started working on my z again..should be finished this summer although thats what i said last spring..im starting with cc'ing my head its an n42 being run with a turbo by the way. what i needed to know was how far along either sides of the combustion chamber should i remove material from to unshroud the valves, as wide as the the valves are or more than that? also when i blend the valve seat area do i want to radius the edge or just blend a nice transition flat with he seats? is there anything different that i should do with the exhaust valve from the intake? should i do anything around the spark plug besides smooth the threads and what should i do with the side opposite the plug? i have looked at some of braaps posts and others but im not experienced enough to look at it and see what i need to do and i dont want my first real attempt at building head to be a faliure..ohh yeah i had a local guy port polish and cc the head last summer but he didnt cc it or put it on the flow bench so i dont know if he even did any good:mad: and furthermore when i cc it i am worried that i might mess up the valve job he did. what do you guys think can i do it without messing up the valve job?

[JMortensen]

Put a couple old valves in the chamber, that will keep damage to the seats to a minimum.

 

As far as how far to unshroud, get the head gasket that you're going to run, put it on the dowels on the head, and scribe a line around the valves on both sides. That line then becomes your limit. Go past the line and you'll expose the underside of the fire ring, and then you'll blow the gasket. So work your way out to the line carefully, and if you're feeling really cautious leave a little margin between your scribed line and the edge of the chamber when you're done.

 

As far as how to blend the seats with the roof of the combustion chamber, I tried to minimize the triangular shaped bumps between the intake and exhaust seats. You can also eliminate all of the casting marks around the valve seats, my E31 had a ring around each seat maybe 3/16" outside of the seat itself. You can transition that ring into the surrounding metal to make it nice and smooth. You should also grind away any excess spark plug threads that may be exposed.

 

Get the How to Modify book, and study the pictures HARD. Be careful, and take it slow and you'll do fine.

[nategdizzle]

sorry i should have explained what i meant about where to unshroud better. should i do the whole perimeter of the chamber or just the area near the valves out to the edge of the fire ring? also i bought the how to book along with a couple of others but i was hoping to hear some nice little tid bits that might help me squeeze the most out of the head. one more thing while im at it, anyone out there know where to get good prices on cross buffs, stones, burr bits and other port polish tools

[Guest Nismark]

Hi,

Here are some chamber pics of a head i ported and unshrouded,

should give you some idea of what to do.Note smooth transition

of seat into port. this head was sand blasted before seats were

cut.It would be a good idea to have a practice on a scrap head first.

Take it slow.

http://album.hybridz.org/showphoto.php?photo=14349&size=big&cat=500&ppuser=21176

[JMortensen]

There is a picture on page 45 of the How to Modify book that shows where to unshroud the valves. That is a rough drawing. If you need to open the chambers up to increase the cc's you can take more metal from a little further around the valve area. Nismark's looks pretty good, but he missed the spark plug threads in the chamber.

[HizAndHerz]

EDIT: I posted this before I read that you already have looked at BRAAP's posts.

 

Here's some good pictures that BRAAP posted a while back. Take a look at his post: http://forums.hybridz.org/showpost.php?p=633690&postcount=10

 

Roughed-in Maxima N-47 chamber shows were material was removed:

Roughed-in N-42 chamber: