97 6SPEED Z

Okay I just got my DIY home ported LT1 cylinder heads back from the machine shop after a competition valve job and having them decked .020", and the machinist tells me I did a pretty nice job with the porting BUT to be sure, (and make sure!), I "blend" the new valve job back. Now what exactly is he asking/telling me to do? What does the term "blending" refer to after a valve job has been done?

Thanks In Advance for all replies.

Mindgame

The hardened seat has an ID near the bottom. That ID needs to blend into the port, making a nice smooth transition... aluminum port to hardened valve seat.

Because of the beryllium copper... the blending shows up real nice in this picture.

http://maxracesoftware.com/Chevy_can...xh_800x600.jpg

Gotta be careful doing this... you don't want to nick any og the angles in the seat.

-Mindgame

97 6SPEED Z

Mindgame, thanks for the prompt reply and that beautiful photo, (wished my ports looked that good!). Okay, so what you are saying is that the ID, (Inside Diameter) of the hardened valve seat located down in the port needs to be "blended" so that there is a smooth transition between it and the aluminum port wall, right? We are not talking about the transition between the hardened valve seat and the combustion chamber, right? What's really throwing me is that that area was largely unaffected by the amount of cutting required by the valve job itself. What I really thought was affected by the cutting required for the valve job, was the transition area between the hardened valve seat and the combustion chamber surface. It looks like machining the hardened seat inserts during the valve job left a little "ring" of undercut aluminum in the combustion chamber, which incoming airflow from the intake valve, (especially when just beginning to open), would see as a definate "step", and possibly cause turbulence?

Let me ask you this: When the valves are fully closed, (i.e. on their seats), and you are looking directly at the valve heads from the combustion chamber side, should you be able to see a little undercut in the aluminum combustion chamber surface just adjacent to the outside diameter of the valves???

As always, TIA for any replies.

Mindgame

Exactly. Throat to seat.

Yes, for some reason I had it in my head that you were asking about the throat only. Sorry bout that.

The top gets a blend over into the first angle (not a "seating" surface). I looked all over the net trying to find a nice clear drawing illustrating this but to no avail. So I created one.

http://community.webshots.com/photo/...71754037FvOrkC

You'll see the blend coming over and going tangent to the first angle. That's what your after. That and the blend at the bottom of the seat going from seat to throat.

I hope this helps.

Are you perhaps refering to that lean-in angle (the first one coming in from the combustion chamber)? You can see that, especially on a valve that has a 30º cut of wide margin behind the seating angle.

Let me know if I'm missing something. I can be thick at times, lol.

edit: fixed link to .jpg

-Mindgame

97 6SPEED Z

Mindgame, you are a Saint! Your drawing made everything crystal clear, (I guess the guy that said 1 picture is worth a 1,000 words, had something there, eh?). The reason my machinist was admonishing me so strongly to be sure and "blend" after the multi-angle valve job he did, was because of the condition of what you call the "top". The first area you mentioned, where the valve seat insert meets the throat of the port is really already pretty smooth and nice, (as I had mentioned earlier). The area where the top of the insert rests against the combustion chamber surface however has a definate step cut into it in the aluminum portion of the head, outside of where the lean-in angle is cut on the hardened seat insert. (The lean-in angle you are refering to is cut completely on the seat insert, right?). Your drawing shows this perfectly as the top "Blend Radius", the blend radius where the valve seat insert joins the combustion chamber, NOT the "throat".

Mindgame thanks (AGAIN!) for taking the time to set me straight on this. It's people like you who are willing to take the time to explain in such detail, that makes understanding some of these "problems" so much easier.

Mindgame

Hey, thanks!

You're right about pictures. Sometimes this stuff can be hard to explain.... different terminology, etc., so a picture can make things very clear. Glad it helped. Besides... someone will ask the same question again. Happens all the time.

That was suppose to be, lead in angle. And yes, it is cut concentric to the valve guide. If you go back and look at that first pic, you can see the blend radius (lead angle to combustion chamber). That's what you're looking for.

Good luck!

-Mindgame