I had my valve seats ground by a local machine shop. They ground the 45 degree face at 45.5 degrees on the intake seats to give a small contact area. I am fine with that, My question is, where should that contact point be on the valve itself. My book says that the contact area should be about centered on the valve's 45 degree surface, but with these, the contact point is about .015 from the outer edge of the 45 degree surface on the valve. Will the seat (or the valve) wear to the point that the contact point is farther in on the valve? Or, is it better to have it out there?

For background, I have ported/polished my heads and installed larger (2.19, 1.88) valves. The exhaust valves have a much larger seat area (to dissipate heat I suppose).

Thanks,

John.

 

ttt

 

Did the machine shop grind the valves for the new diameter valves? It sounds as if the valve diameter is too small for the seat. Are they new valves? They shouldn't have to be touched, just installed right out of the box. It is important to have the contact area in the middle of the valve face. How are you checking the contact point.

 

I had them enlarge the seats, and then I blended the bowls again. Then I had them do the final grind. I did have to face the valves themselves - I think that even the best of new valves need that. I am checking the contact point by putting prussian blue on the seat, putting in the valve, and tapping on the valve. That gives some idea. Then I rotate the valve against the seat to get a good ring.

 

Well, it sounds like you checked it correctly. It contact area is just a little skewed. It's my opinion that you will probably be ok. How serious of an engine are you building? Are you running killer valve springs? That may cause some concern.

 

Sounds o.k. to me but you're right about the "surface area" ...there needs to be more contact area with the valves.
I may be reading your post wrong - but 'new' valves will "stick" up a little with the appearance that they're not 'seated'....
Older, worn valves are often 'countersunk' - bad news - this causes valves to burn....
Maybe you should go for the 3-angle valve job if you're concerned about it.
...but it'll take some more dough ($$$) :(

 

I have a three angle valve job on the heads. I am using single spring valve springs that Crane recommends for my cam. I'm not trying to build a killer engine or anything like that, but while I was replacing my cam I decided to port and polish, and then it snowballed into repalcing the valves, valve springs, push rods, etc.

Thanks for the info.

 

Here is a picture of what I am talking about.
You can see that the contact area (blue) is very close to the edge. Shouldn't it be farther in on the face?

 

looks good to me,but they should have ground a 20 degree back angle on the valve to increase low lift flow. :chevy

 

I guess I could do that. I ground the valves themselves on my brother's valve grinder. Should b pretty quick to do that. Should I do the exhaust valves that way too?

 

yes you can also do the exhaust valve. have the backangle come within .010/.015 of the seat on the valve head. use the bluing to see were the seat is on the valve. :chevy

 

I've been doing valve work for a long time... professionally, and I would not let a set of heads go out the door like that.... not with my name on the job.
1) The dye only tells you part of the story
2) That seat will move up toward the valve OD as it wears, making it even more un-reliable.

I would lower the seat toward the center of the valve more and widen it just a tad.

Not a big deal if you're a competent machinist.

 

if you are looking for max air flow the farther out to the edge of the valve head and the narrower the seat the better. if you are after long valve seat life,move it in but widen the seat. it depends where your priority is ,max performance or longer life. the use of 45 degrees and 45 1/2 degrees comes from the chevy shop manuals. :chevy

 

I guess that for a car that is only driven a few thousand miles (<3000) per year, long life probably is not as big of a deal. However, I'm not looking for ultimate performance, and would rather have reliability. I should be able to just touch the seats with a 30 degree stone to move the seat in, right?


[Modified by john73bb, 6:26 AM 4/19/2002]

 

I don't subscribe to the 45/45.5 method of cutting valve seats.
That is referred to as an "interference angle" technique.
Its primary purpose is to hasten valve/valve seat break in.

I cut seats at 45, valves at 45.
Of course, this is "Chevy Ville". Other designs use different angles... all engines are not 45.
I use compound to seat the valves before final assembly... and yes, I do manage to remove every last tiny little molecule of it so it won't affect the quality of the job. This way, my heads do not require a "break in" period.
This also high-lites any possible machining errors that other methods, including dye, will miss.
This includes angle variance due to un-trued cutting tools... it happens.

I cut the top angle to give me a reference point, and to bring the seat in on the valve face...
So... generally, yes... cutting the top at 30 will bring it in. I also use a 15 on the top occasionally.

The problem is, this will also narrow the seat, and then you will need to cut the 45.5 again.

I have no stones or carbide cutters set up for 45.5 (or 46 as is also commonly used).
I have no need for them.

Clem is right about the choices to be made.. it's not all "cut & dry".

I would guess, though, that most of use envision ourselves as Mario Andretti when we are in reality Gomer Pyle.
(Yup. Uh Huh. Yup.... me too)
In that case, cutting a set of heads strictly for non-street useage (I don't mean plowing the north 40) would be a little on the iffy side.
That's why I expressed my opinion to bring the seat in a little and widen it.
I don't read about this stuff... I actually cut the heads & valves, on my own equipment.