781 bb Chevy heads can I cut spring seat?

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drifter
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781 bb Chevy heads can I cut spring seat?

Post by drifter »

I have a set of 781 bb Chevy heads and the intake valves has a spring height of 1.750 can I cut .100-.130 off the spring seat so I can get a 1.850-1.880 spring height?
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Re: 781 bb Chevy heads can I cut spring seat?

Post by vortecpro »

drifter wrote: Wed Jul 01, 2020 6:34 pm I have a set of 781 bb Chevy heads and the intake valves has a spring height of 1.750 can I cut .100-.130 off the spring seat so I can get a 1.850-1.880 spring height?
Date code of the heads?
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Re: 781 bb Chevy heads can I cut spring seat?

Post by racear2865 »

My I ask why you did not go with a longer valve
reed
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Re: 781 bb Chevy heads can I cut spring seat?

Post by pdq67 »

FWIW, Chevy BB heads have two installed spring heights.

At 1.800" later and at 1.880" earlier height so do what you want.

And there are various height keepers as well as top spring holders so you shouldn't have to cut anything if you do your homework.

My 496 has .050" taller keepers on it to get to the spring installed seat pressure that I wanted.

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Re: 781 bb Chevy heads can I cut spring seat?

Post by ProPower engines »

drifter wrote: Wed Jul 01, 2020 6:34 pm I have a set of 781 bb Chevy heads and the intake valves has a spring height of 1.750 can I cut .100-.130 off the spring seat so I can get a 1.850-1.880 spring height?
I sonic check the seats and found I can go .050 deeper. I would not go any deeper then .050 then use a +.050 lock to get to 1.850". that way your in the ball park and its an easy change to make.
And most spring seats are larger then 1.550 any way so if you go +.050 deeper it will align the spring on the seat that way no real need for a locator on an iron head as long as the spring pressures are not crazy.
If you installed a larger valve you must not have cut the new seats deep enough. When doing a + size valve I always cut the 1st seat then check installed height with the hardware I have on hand for the job. And if its customer supplied hardware then its always the best way to go so you don't have any surprises like this at assembly time.

Took me forever to train my apprentice to do that every time when installing larger then stock valve size of installing valve seat inserts.
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drifter
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Re: 781 bb Chevy heads can I cut spring seat?

Post by drifter »

Vortec Pro they are A16-75

Int valve size is 2.065
5.230. oAL

Ex valve 1.720
5.360. oAL

Exhaust springs have a rotator on the bottom and intake have none
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Re: 781 bb Chevy heads can I cut spring seat?

Post by vortecpro »

Too Pro Power: Are you aware 781 head castings, depending on the year have different spring pocket depths? I would guess the OP has 1975 or newer castings. If the OP wants to post what year castings he has I will tell the OP exactly how far he can cut the intake spring seat pockets.
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Re: 781 bb Chevy heads can I cut spring seat?

Post by vortecpro »

drifter wrote: Wed Jul 01, 2020 9:16 pm Vortec Pro they are A16-75

Int valve size is 2.065
5.230. oAL

Ex valve 1.720
5.360. oAL

Exhaust springs have a rotator on the bottom and intake have none
Ok.......you will cut the intake pocket .070 and use a .050 keeper, simple.
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Re: 781 bb Chevy heads can I cut spring seat?

Post by drifter »

Thankyou Vortec Pro👍
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Re: 781 bb Chevy heads can I cut spring seat?

Post by pdq67 »

vortecpro wrote: Wed Jul 01, 2020 9:22 pm Too Pro Power: Are you aware 781 head castings, depending on the year have different spring pocket depths? I would guess the OP has 1975 or newer castings. If the OP wants to post what year castings he has I will tell the OP exactly how far he can cut the intake spring seat pockets.
I already posted this!

Early heads are 1.88" and later heads are 1.80" stock installed spring height..

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Re: 781 bb Chevy heads can I cut spring seat?

Post by ProPower engines »

vortecpro wrote: Wed Jul 01, 2020 9:22 pm Too Pro Power: Are you aware 781 head castings, depending on the year have different spring pocket depths? I would guess the OP has 1975 or newer castings. If the OP wants to post what year castings he has I will tell the OP exactly how far he can cut the intake spring seat pockets.
Yes I was.That was why I only suggested go +.050 deeper. Without the year it was a safe suggestion that would get him where he wanted to get to.
As I mentioned I always sonic test the spring seat area as I have found a few thin seats over the years but generally speaking if +.050 is not enough there is a issue with the valve length or seat heights. I see this more on exhaust seats guys have installed and do not check the spring installed heights and rarely do they if ever get the seat inserts parallel to the deck faces anyway making the job harder for themselves in the end of it all.
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