I'm thinking of going with a 3-angle valve job. My heads are from 1970 (# 1233472) wich doesn't have the hardend valve seats yet. Can the original valve seats be cut to these 3 angles? Or are new valve seats neccesary? Or recommended? What are the gains of such a 3-angle valve job by the way? I'm planning on doing a mild home port job (port match heads and intake, some bowl and valve guide work). And I will install a performance cam (Lunati #33203). And high comp pistons and headers. With such a setup, will I benefit a lot from a valve job?
People talk about "3-angle" valve jobs as if they were something special. They're actually the LEAST expensive way to do a proper valve seat job. The "first" angle is the actual seat cut; the seat is narrowed and positioned by taking top and bottom cuts--the second and third angles. Now, a true "three angle valve job" will also put 3 angles on the valve face--and that's often not done when cost is a more important factor than performance. If I were to ever "valve job" another set of old iron castings, I would have hardened exhaust seats installed just as I've had done in the past--but--I'm all in favor of aftermarket iron or aluminum castings whenever practical. There's talk of non-Chevy engines having additional nickel in the iron casting; and that hardened seats are therefore not required--but--I say if the added nickel in the iron was satisfactory, GM wouldn't have provided hardened seats starting in '71 or '72. The BIGGEST benefit to a valve job is to correct defective valve sealing. If your valves still seal--improvements are considerably smaller; and require more machining skill 'n' trickery than what was provided by GM when the heads and valves were being made to begin with. Consider trying to find new valves with larger-diameter heads if they'll fit in the chambers. Going to a larger valve allows the seats to be ground on virgin iron, the valve seat doesn't recede into the head the way they do when re-grinding the old seat. Valve stem tip height will be important; the tips must be at a consistent height and the CORRECT height, or you wind up with valvetrain geometry issues.
Thanks for the reply. I don't want to sink too much money into this engine just to sqeeze any lost pony out of it that I might can with this setup. And yes, I realised that the valves will be sitting a little higher into the seats if you cut the seats. Is this a big problem? Of course it will be if the height of all the valve stems is not the same. But if they are all the same height? Still a problem, and need to be cut? I might run into rocker ratio issues don't I? About new (hardened) valve seats, this is what I found in the TA catalog about valve seat replacement on 350 heads: In most cases we do not install hardened intake seats, we install them as needed. For one, the Buick cylinder heads had a high nickel content which essentially made the entire head hardened. Also, the water ports are very close to the intake seat area, and the head can be compromised if a shop rushes into changing all of the seats. So yeah, now I'm kinda hasitated to just go for new valve seats. I don't know if the valves sealed good before. I bought this engine as is. It ran good before it was pulled. But I have no idea how the valve sealing was. Right after I bought this engine I tore it apart for a rebuild. Some weeks ago I already grinded the valves. I could easily do this at work. I grinded them to the stock angle of 45 degrees. Just slightly though, the valves look nice, just freshed up the surface.
Sean, yeah that is very important. I'm not going to put the heads back on the engine before I know 100% sure the valves seal correctly. At work we have a vacuum device for this. Works great. I hope Schurkey or anyone else can say something on the valve stem height I mentioned in my previous post.
to keep from sinking the valve down in the head the main angle is ground in and then the angle that goes down into the pocket,,,, and last the lead in angle, which is just a touch, is done.... The pocket cut does 3 things,,, it opens up the pocket a bit, and raises the valve seat, and narrows the valve seat.... never, ever, reverse the stone and ''backgrind '' the seat to narrow it....that sinks the valve down into the head....
Don't do a 3 angle (or any others) unless the valve guides are all in good shape! Especially if you have guide issues the 3 angle will not seat well.
The valve tips all have to be at the same height; and that height has to be the RIGHT height. There is some little amount of tolerance; and things can change if you're willing to play games with the rocker shaft mounts and the rocker arms themselves... ...BUT--for a stock valvetrain--you MUST get the valve tips at the correct height, or rocker geometry can become a problem. Be aware that rocker geometry and lifter preload are not the same thing. Just because there's lifter preload doesn't mean the geometry is correct. I don't have the specification for valve tip height, though. No doubt someone else here will.
If you grind off "x" amount of stock from the valve face, then you must dress an appropriate amount from the end of the stem since you are "dropping" the valve deeper into the seat. It is not a linear amount given you are taking "x" amount off the 45 degree seat on the valve and the end is at 90 degrees. Anyone who has ever done valve jobs or ground valves on a Kwik-Way will know what I am talking about........
