Technical valve seat width

Wanting to do 30/45/60° seats with a 3 angle tool. Valves are small, 1.050 exh and 1.150 Int. So how wide should I make the seats? Spring pressure is about 60# on the seat, rpm 7500 +/- 1000. Valves will be back cut to lighten and for flow. How does .045 int and .060 exh sound?

 

That is narrower than I used to do them. most of the ones I did were just over .100 but I am seeing anything from .065 .100 when I looked it up right now.
I'm going to call it engine builder's personal preference and that things may have changed a lot in the past 25 years since I was doing valve jobs and teaching students to do them.

 

'bout 2/3 the way out is how we do them on old Harley floater motors....

 

I typically cut to about .060 max and had good success

 

My experience has been that the narrower the seat, the better the short term seal but the shorter the life of the valve job. My usual compromise was .060 and .090 for acceptable life and good performance.

 

.045 and .060is just fine,most of my street and hot street work is in that range.
No one mentioned valve guides.
If the guide is straight and true,it helps longevity 10 fold,heat transfer from the valve is better. A quality valve and correctly sized guide is a must.
A new guide or service liner,then honed to size not reemed.
The valve job starts at the guide.
In time the seat with gets wider with use,so do worry about it. As long as your guides are good and seat concintricity is good your service life will exceed original oe.

 

Doesn't the valve determine the width of the seat?

 

They are referring to the contact area between the valve and the seat in the head


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I understand that, I make my seat width narrower than the width of the valve

 

If this were my cylinder head -

Intake = .060"
Exhaust = .090"

Normally wider will result in a loss of quality flow.

Mike

 

@seb fontana generally speaking wide seats on a huffed mill and narrower on a naturally aspirated motor.

On a small valve I would be shooting for .06 to .12 probably closer to the .06 side. I have a tendency to run a wider seat on an air cooled motor than I do on a liquid cooled motor. But it is a personal thing I think and I cannot give you any good logic on it.

 

Valve guides are good at .312, I have a choice of .310 or .315 stems so any clearence can be made. Beaner brought up what I forgot; eventually I do plan to get to a few pounds of boost.. I left the compression at 8:1.. My thought beyond performance gains of narrow seats is the ability for the valve to "bite through/Crush" any trash, carbon, etc. Stock seats were in the .075/.090 range, valves have just over .100 face. I put my dail calipers at .045 and .060 and I get nervous, sure isn't much!

 

I always shot for 1/16 ".

 

X2 what gary says. I love the job my Sunnen valve guide hone does.
What is the intended use of the engine? You mentioned a 7500 RPM intended operating range. Is it for a street application or a race application. Race cars can get by with narrower seats further out near the outer edge of the valve face. Never at the extreme edge of the valve. For street applications I go a little wider. Longevity trumps optimal flow here.

 

On the intakes I run .0014-.0015 ,exhausts .0017-.0018 except for the two siameed exhaust ports I run them at .0020 .
A proper bore gauge ,split type I use,or a sunnen is needed,without a bore gauge you are just guessing . Pin gauge,go/no go or a ball style snap gauge like mondello use to use in his classes,cannot show how straight it really is. Using the right measuring tools is a game changer. I use to reem with carbide reems, measured them with a bore gauge and never picked them up again.
When the guide is straight to the .0001 the valve doesn't thrust,hits the seat true and consistant and durability and longevity is increased.

 

Why do you feel a carbide reamer won't ream a guide properly ? Can you explain how you check straightness? Do you use a precision air guage for verifying the inside of the guides?

 

I use a mitatoyo split bore guage it will read the bore of the guide as you pass through it,a air guage is fixed to a table or stand,really can't hold the head to use one.A fixed guage just reads the tightest point. Every guide I measured done with a reemer always shows tight in the middle,less deflection on guide supported better in the middle. And they generate a wavy pattern seen on the guage while passing through it. Honing the guide gives a perfect finish and you can dwell while honing the guide to ensure straitness. If I end up .0002 taper or off my size. it's alot for me.
You will get a thousand people tell you it's overkill, what works and what works well are two different things.
You won't find a auto parts machine shop doing this type of work.go to a real speed shop, someone with a reputation of good work ask what they do. I am not far off and yes,this is what I do.

 

Unless your machinist also builds race mills.....that's a plug for Paul at balsinger machine, Guthrie, USA.....third generation machinist, and a great guy...honest to boot

 

Well I got tired of trying to port the valve bowls around the guides so I knocked them out (pressed). I can get new guides in cast iron or bronze. Is one really better than the other for the size of the valves [1.150&1.050-.310 stem]? Rpm at 7500 is conservative, being a Crosley, over that and the trans becomes issue. I figure I can lean on the tight side for stem clearance as there should be no side load from rocker arms as it is sohc; cam, lifters, valves. Or am I thinking backwards? I got a seat cutter that can swing doing both valve diameters and seat widths [just barely], arbor too.

 

Bronze guides will transfer heat better.
A radius valve job will gain you about 3% hp.

 

Up date. Stalled for three months, hand issue with Rheumatoid arthritis. They swelled up so much I couldn't bend my fingers [hurt], got meds and heading back to usable. Got a eurolift too, made things a little better but ways to go..My hands have lost a lot of callas except for my right hand; no not from that. From running the computer mouse..

 

Finally back to tinkering some, mostly thinking though. How wide should the 30° top cut be? If the spot face for the valve is a lot bigger than the valve [not like factory where it is just enough] does it still help?

 

For me the top cut was set by the seat to the valve that would leave a margin on the valve.

 

Finally back at it. Bronze guides installed, stock clearance is int .001/.002 and exh .002/.003 which is what I have them at now. Toned down my dreams a bit, max rpm only needs to be around 6k so rpm doesn't drop too low when shifting up. Machined turbulators to equal height, will drop block around .090 to get compression up to 9:1. Working on setting valve seat cutters [neway], got to find the right mag glass to see what the hell I'm doing!

 

Seb : Are you doing a restoration or a performance motor? I started with a Crosley 60yrs ago, & "bone stock" those easily went 8500 consistently & reliably, & with a few minor modifications(by todays standards, anyway) would go well over 10,000! Check with the guys that ran 3/4 Midgets, "H" modified sports cars or "45" Hydroplane boats, or at least listen to a tape of the engines & your ears will tell you what sort of RPM these engines will turn!!