ede

what is considered too much? is there a manual that has these specs in it or is the width specs the same for all engines? thanks

No4NJunk

Are you asking how much of a radius cut you can put on the seats (ie- for use with larger valves)??? I used to know this incredible site that had all kinds of machining specs for SB heads. I'll try and find it again.

ede

no i want the width of the seat, nothing fancy just general engine specs, that aren't in a manual. or to put it another way when do i need to narrow the seat width?

ede

didn't figure i'd get an answer over nite. been thinking about this a bit more i know i can machine the seat. can i grind it to make it narrower? seems like i could and if that's the case what would i use? 15* or 20* stones seem like a logical choice.

RB83L69

I was kind of hoping somebody would answer that knows more about this than I do, I'm no expert. I don't know if there's a "spec", as such... most people seem to shoot for about .060" or so on the surface where the valve actually is going to seat, and then the other 2 or 4 or however many angles about .025" or .030" each. Seems like it wouldn't matter how narrow that is as long as the valve can lap to it correctly, which would take maybe .030" to guarantee a good lap. Yes you could grind behind it to make it narrower, that would almost be like "porting" the throat right there; you'd want to make sure you leave enough for a 30° or whatever cut right behind the main one though.

Another thing alot of the race shops will do is to round over, or at least cut some angles, on both the port side and the chamber side of the valve, such that there's a smooth radius around the edge of the valve or at least not a sharp 90° on the back and a sharp 45° on the front. That makes a significant difference to the flow at very low lifts.

ede

i've been searching the net and have found .030-.050 for intakes and .060-.070 for exhaust. i have a cutting tool i picked up at an auction that uses waht looks like two 1/4" lathe tools and is turned by hand. the more i think about it the less i like it and will use the seat grinder. in my web search it says to use 15* stones to narrow the top of the seat and move it downward and a 60* stone to narrow the bottom side and move it upward. the main thing it to keep the contact area in the center of the seat to reduce carbon build up and excessive heat and valve buring. one thing i don't quite understand is if i can use two 45* cuts or if i have to use 45* and 46* for interferance fit? my manual list the 45* and 46* but i don't really see where it would make any differance as long as you had full contact around the seat. i'm sure most if not all machine shops grind all the heads either for interferance fit or with two 45* seat and valve angles.

Vader

I've seen conflicting data on that. Some seem to say that a wider seat makes for a better seal and heat transfer, while others say that the increased pressure (PSI) on a narrow seat actually helps sealing and heat transfer, especially on the exhausts. I don't know, but on the surface both theories have their merits. Good luck on finding a definite answer.

ede

i'm not sure what to think or believe. i ground some valves and seats last week end and it appears i did a decent job of it. i might do a head or two and not worry so much about it and see how it goes.

Mark A Shields

Wow, I just wanted to say, I haven't seen you 3 guys stumped like this ever, I believe.

nice, to know you're mortal.

No4NJunk

Ede Here's what I got,

Ok. As a rule of thumb, the ideal seat width for intake valves is usually around 1/16". For exhaust valves, it’s 3/32" - or whatever the manufacturer specifies. OR.... about .060" to .080" intake and .080" to .100" exhaust. Seat width is important for tight compression sealing and proper valve cooling (makes sense). If the seat is too narrow then wear resistance and heat transfer will suffer. It its too wide then there may not may not be enough pressure to provide a tight seal. Also wider seats tend to trap more deposits (holding the valve off of its seat).

In reference to seat cut. The point at which the valve and seat mate is also important. If the area of contact is too high on the valve face (too close to the margin), the valve may be sunken into the head. This increases installed height, upsets valvetrain geometry and restricts free breathing. If the area of contact is too low on the face (too far from the margin), the valve will ride too high on the seat. As the engine warms up and the valve expands, the contact point moves down the valve face away from the margin. The valve may lose partial contact with the seat causing it to lose compression and run hot. Ideally, the valve should contact the seat about one-third of the way down the valve face about 1/32" from the margin so there is about 1/64" of overhang between the margin and top of the seat.

ede

that's pretty much in line with one or two of the sites i looked at today. guess i'll play around a bit more with my scrap head and see what i can do with it. last week end i did find out the wrong way to dress a stone and cut the tip off my dresser.

RB83L69

This is one of those things where there is no absolute "right" answer. It's a compromise: you give up one thing to get another. Your typical production head rebuilder will go for wide seats, a racing shop will do narrow ones, for a number of reasons. For one, it's alot cheaper (less attention to detail) to make wide ones, you just jam the stone in there and you're done. Narrow ones require some finesse. Narrow ones wih lots of angles all around them produce lots of HP more than wide ones do, but all of that ceases to make any difference after a motor gets a few thousand miles of gasoline buildup on everything. Wide ones will last longer between valve jobs. So what do you really want your motor to do? How are you going to use it? The intended usage makes a difference.

I don't think I've ever seen a street head with seats as narrow as .030" from a good head builder. I've seen circle-track motors set up that way though.

This is a good example of why you don't buy machine work from the low bidder: somebody that understands this sort of thing, and can give you the right compromise for what you tell him you're going to use the motor for (or what he figures out the reality is regardless of what monkey-spank you tell him), and will take the time to execute the job in the chosen best fashion rather than just running them across his machines without any thought, is worth what he charges.

ede

the valves i did last week ran in the .050 - .060 range. you're right it isn't hard to do. i'm pretty sure they would work. but i never put springs back on to see if they sealed or not. my main worries was too narrow a margin on the valves, especially the intakes get pretty thin and making the seat to wide and burnng a valve. i'm not going to try for any trick preformance valve jobs ,i just want to be able to do my heads and maybe a few other every year to make a little money to cover the investement in these tools. rb if you don't have anything to do this week end you can stop by and show me a thing or two with all these new tools. i'd buy you a beer and pizza.

No4NJunk

Sorry ede but I was in a rush when writing my previous post and didn't have a chance to answer your question on the seat cut angles.

The guides must be reconditioned or replaced before doing the seats because all seat work is done by centering off the guides. I'm guessing here that yours are fine. Choices here include grinding or cutting. Grinding requires at least three steps for each seat and kicks up a fair amount of abrasive dust. You also have to be careful to keep the stones properly dressed to maintain accuracy. Cutting, on the other hand, is cleaner and faster especially if all three angles are cut at once. But cutters are more expensive.

The basic procedure for grinding a seat is to select a wheel 1/8" or larger than the seat. The grit of the stone depends upon the seat material. For best results and fast stock removal, use coarse stones on hard seats, and a finer general purpose stone for cast iron seats. Insert a pilot tool into the valve guide to center the grinding stone. Use a spring under the grinding stone, then grind the seat with a gentle bouncing motion on and off the seat. This reduces chatter, prevents the stone from loading up with particles and gives better overall results. Remove only as much material as is needed to clean the seat. Don’t get carried away because you can grind away the hardened surface layer on induction hardened integral seats. You can also sink the seat too deeply into the head. Grind off only enough to get rid of the discoloration, pitting and burning on the seat. Once this has been done, switch wheels and use a 15° or 30° stone to cut the top angle on the seat to locate it with respect to the valve face. If the seat is too wide after cutting, narrow it by cutting the throat angle using a 60° or 75° stone. Be sure to dress the wheel frequently. For best results, this should be after every couple of seats. After grinding, check concentricity and seating with a vacuum tester or Prussian blue. This will tell you if additional work is needed. If the point of contact is too low on the valve face, raise the seat by enlarging the throat cut with the 60° or 75° stone. If the seat contact is too high, lower the seat by topping with the 30° stone. The basic procedure for refinishing a valve seat by cutting is essentially the same as grinding except that you’re using carbide cutters instead of grinding stones. The seat is cut, then positioned by making the top cut at 15° or 30°, then narrowed by making the throat cut at 60° or 75°. If the equipment makes all three cuts simultaneously, then it’s a one-step operation. Concentricity should still be checked, however, to make sure everything’s right.