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Old 05-13-2013, 03:13 AM
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781 heads,installing big valves

If I have larger valves installed,can the larger valves,2.19/1.88, be cut into the old seats or do the seats have to be replaced as well? The exhaust valves are perhaps to much bigger than the old 1.72 valves but the intakes are only 12 hundreds of an inch bigger in diameter which works out to be only 6 hundreds of an inch bigger around the circumference of the valve seat which I believe(hope) the original valve seat inserts should be large enough to handle. Any machinists out there willing to help answer this question?

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Old 05-13-2013, 05:58 AM
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Seats are re-cut for installation of the larger valves.
A good machine shop will use what is called a "Serdi" profile cutter for the work. Followed by a "Bowl hog" to blend into the bowl.

The Serdi has a pattern designed into a flycutter. This cuts all angles and smothes transition areas. The bowl hog then takes out any remaining sharp edges. All that is required then is a careful hand blending of the exhaust short side radius.

Exhaust seats can be replaced with hard inserts. But for the last several years, to save customer money. I have been cutting into the stock hardened seat area and there is enuf material that hard seat remains.

Also have the guides shortened and cut for positive seals. Or if a mild cam, single spring situation. Have guides shortened and use Buick 455 seals.
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Old 05-13-2013, 02:58 PM
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Originally Posted by BOBCRMAN@aol.com View Post
Seats are re-cut for installation of the larger valves.


Exhaust seats can be replaced with hard inserts. But for the last several years, to save customer money. I have been cutting into the stock hardened seat area and there is enuf material that hard seat remains.
My problem over here is that I see an insert on the exhaust already(they install hardened seats here so the cars can run on natural gas,LPG, which costs less than half the price of gasoline (benzine) per liter,60 cents Vs. 1 euro70cents) so I must replace the exhaust inserts but good to know I can recut the stock sittings without a problem. I'm thinking of going big intakes2.19 with the small 1.72 exhaust like what came on the early 427's. My buddy albanese had a 425 hp vette in 66 and he pulled all the way to over 7 grand with it so I figuare the combination should work in an engine though slightly bigger that is only going to see 5500-5800 max(unless I'm losing ). My lift is only .550 so I don't think I'll need to trim the guides but I'll check to make sure. Thanks for the comprehensive answer,a big help.
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Old 06-23-2013, 07:50 AM
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Originally Posted by BOBCRMAN@aol.com View Post
Seats
Exhaust seats can be replaced with hard inserts. But for the last several years, to save customer money. I have been cutting into the stock hardened seat area and there is enuf material that hard seat remains.

Also have the guides shortened and cut for positive seals. Or if a mild cam, single spring situation. Have guides shortened and use Buick 455 seals.
yankee phil: Took your advice and bought all big valves and cut new seats in the stock hardened seat area's. Finished the 60 degree cut into the bowl and it seems like there is room (in the exhaust port wall)to make a steeper cut like 80 degrees to better blend into the port . I know there's a water jacket by the exhaust and it's the biggest diameter enlargement of the two,I worry about a water strike.
Am I going too far, is 60 degrees enough to get a good blending angle, do I risk hitting water if I extend the cutting with a steeper 80 degree cutter? How far into the pocket can I blend in with the 60 degree cutter. I've blended into the pocket about 3/8ths-1/2 inch already with the 60 degree cutter. Any advise would be greatly appreciated .
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Old 06-23-2013, 08:31 AM
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I use a 70-80 degree just a small amount to blend. 1/8-3/16". Then hand blend to remove any small edge. This is after a Serdi profile cutter, which cuts the basic angles.

Yes the port wall gets thin. I have never had problems with my method. But I have had to repair jobs from other shops that oversized the port. So I stay on the conservative side.

On your exhaust side.. You can use a 1.84" exhaust valve cut into your hard seat. These are a little harder to find than 1.88", but were stock exhaust on early GM performance heads from the late sixties. I believe Sealed Power still lists them in stock length.

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Old 06-24-2013, 01:42 AM
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Originally Posted by BOBCRMAN@aol.com View Post
I use a 70-80 degree just a small amount to blend. 1/8-3/16". Then hand blend to remove any small edge. This is after a Serdi profile cutter, which cuts the basic angles.

Yes the port wall gets thin. I have never had problems with my method. But I have had to repair jobs from other shops that oversized the port. So I stay on the conservative side.

On your exhaust side.. You can use a 1.84" exhaust valve cut into your hard seat. These are a little harder to find than 1.88", but were stock exhaust on early GM performance heads from the late sixties. I believe Sealed Power still lists them in stock length.
yankee phil:Thanks for the advise,my measurements 3/8-1/2 were way off when I checked it,I was remembering the seat along with the blend cut in my head. Good advise on the valve size 1.84 as I've seen this in books that I've read and wondered why the middle size. Unfortunately I've already cut the seat's and bought the 1.88's so I'll have to keep an eye on it. I got some neway cutters . I have used neway system for a long time now,I remember when they first came out and the shop I worked at bought a set,I feel in love after having used stone and die cast cutters for so many years,It was like when the first clicker torque wrenches came out,like a breath of fresh air . Too bad you can't harden the seat yourself with the heat to cherry red and quench process ,sounds scary to do with cast iron . The only problem I have with the neway stuff are the chatter marks left on the seat, I have to go over it very softly a bunch of times to smooth'em out. I have to say though the metal felt hard to cut even out to the 1.88 size so I'm hopeful about the strength of the seat. Your advise was invaluable,greatly appreciated.
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Old 06-24-2013, 04:55 AM
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I have used the 1.84" valves in certain 366 truck heads. These heads have small chamber, don't flow too bad with 2.19" intakes but are real thin on the exhaust side. Make good heads for flat top piston street motor. Can't remember the casting no. But I did several sets and got rave reviews from customers..Yes, I also have the Neway system. I'm an old stone man but the Neway cutters are great in many situations. Their factory and headquarters is twenty miles from here so getting the latest stuff is a breeze. Glad to help..BOB

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