"Light tight" valve jobs

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Re: "Light tight" valve jobs

Post by joespanova » Sun Jun 10, 2018 8:06 pm

My way of thinking has always been , if the angles are right , the seats are concentric , ,the right width and light tight ( no springs )............I've got a good valve job.
Last edited by joespanova on Sun Jun 10, 2018 8:08 pm, edited 1 time in total.
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Re: "Light tight" valve jobs

Post by cjperformance » Mon Jun 11, 2018 4:26 am

Prussian Blue is great if you are gentle on the valve. On a big valve you can easily get a 'good' blue impression if you clap the valve onto the seat with any sort of force. Use light finger pressure only.
Craig.

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Re: "Light tight" valve jobs

Post by mag2555 » Mon Jun 11, 2018 7:42 am

I get the the valves and seats free of oil then I color up the seat on the valve with a big black marker and drop it down in the guide and spin it by hand from the stem side while yanking on it.
If the black does not transfer over nice then it's time for a valve job, hopefully doing the in head seat cut with a stone just in the same way a stone is used to reface the valve itself!

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Re: "Light tight" valve jobs

Post by 1972ho » Mon Jun 11, 2018 12:44 pm

CJ just a question about a light clap of the valve to the seat for a impression,isn’t the valves working harder than that when the engine is running I mean when the valve closes with 150 to 450# of seat pressure seems you should be able to slap the valve down harder to see the impression.Just a thought?

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Re: "Light tight" valve jobs

Post by exhaustgases » Mon Jun 11, 2018 2:37 pm

1972ho wrote:
Mon Jun 11, 2018 12:44 pm
CJ just a question about a light clap of the valve to the seat for a impression,isn’t the valves working harder than that when the engine is running I mean when the valve closes with 150 to 450# of seat pressure seems you should be able to slap the valve down harder to see the impression.Just a thought?
Yes and then there is the spring pressure, that is a bit more than a light finger pressure, then of course there is the firing pressure added to the closed spring pressure.

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Re: "Light tight" valve jobs

Post by cjperformance » Mon Jun 11, 2018 6:30 pm

1972ho wrote:
Mon Jun 11, 2018 12:44 pm
CJ just a question about a light clap of the valve to the seat for a impression,isn’t the valves working harder than that when the engine is running I mean when the valve closes with 150 to 450# of seat pressure seems you should be able to slap the valve down harder to see the impression.Just a thought?
To start with as good a VJ as possible you need to forget the springs. You can have a seat so far off that you dont need light to see tha gap and put a spring on it, the valve flexes oves and it will seal. Think of that with a solid roller spring pulling on that flexed valve when running and the impact on valve fatigue, the seat, the guide etc.
If you aim for a seat that is as concentric as possible and centeres in line with the guide centerline AND certainly no more off center than half of the valve guide clearance then you are off to a good start.
When i say light clap onto the seat, that light! As in 'just' enough to get a transfer of blue. You should be able to blue the valve, touch down on the seat , clean the valve, touch down again and get a reimpression of blue back from the seat. When the seat in not concentric, you can actually feel it without even using blue.
Craig.

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Re: "Light tight" valve jobs

Post by Keith Morganstein » Mon Jun 11, 2018 9:04 pm

Quoting an old post about Prussian blue
Keith Morganstein wrote:

Check seat to valve contact with Prussian blue paste. Clean the seat and valve. Apply a thin smear of Prussian blue paste to the valve face.

Position the valve in the guide and drop the valve into the seat. ( A tap with the finger will help it hit the seat) Do this once , with NO rotating of the valve. Pop the valve out pushing from the stem end and carefully remove the valve so as not to smear the paste. This will give you an accurate contact patch.

Important: DO NOT rotate the valve when checking contact!
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Re: "Light tight" valve jobs

Post by cjperformance » Mon Jun 11, 2018 9:52 pm

Keith Morganstein wrote:
Mon Jun 11, 2018 9:04 pm
Quoting an old post about Prussian blue
Keith Morganstein wrote:

Check seat to valve contact with Prussian blue paste. Clean the seat and valve. Apply a thin smear of Prussian blue paste to the valve face.

Position the valve in the guide and drop the valve into the seat. ( A tap with the finger will help it hit the seat) Do this once , with NO rotating of the valve. Pop the valve out pushing from the stem end and carefully remove the valve so as not to smear the paste. This will give you an accurate contact patch.

Important: DO NOT rotate the valve when checking
contact!
^^^ yes as above.
On that point, if the valve is say out by .001" and the seat is out by .001" and you rotate the valve you would think the seat was perfect. Even if the seat or valve were concentric and the other was a little off the blue will be swiped across the seal face and can be misleading.
Craig.

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Re: "Light tight" valve jobs

Post by Frankshaft » Thu Jun 14, 2018 10:13 am

One of my checks is for light. If I see light, it needs further work. It sounds like you just need to bite the bullet and freshen the vale job. The valves are likely cupped, and the seats don't sound mint. Grind valves at a minimum and recheck maybe. I just did that for a guy last week. They were trying to limp a set of OLD 861 gm bowties that have had a gazillion valve jobs, and have been ran hard put away wet. The seats in the heads were fine, but sunk, didn't want to sink more if not needed, the valves were cupped. I just ground the valves for him and re checked, it was fine. Itt'l run.

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Re: "Light tight" valve jobs

Post by zums » Thu Jun 14, 2018 7:48 pm

No one believes in accurate concentricity gages any more? , when i check a seat and valve face in v blocks and they are within spec i dont need to lap, bounce, pour a chemical in the port, stick a light in, they all pull up to 20" vac with a hand pump and no spring, why guess
Tom

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Re: "Light tight" valve jobs

Post by Frankshaft » Thu Jun 14, 2018 7:59 pm

zums wrote:
Thu Jun 14, 2018 7:48 pm
No one believes in accurate concentricity gages any more? , when i check a seat and valve face in v blocks and they are within spec i dont need to lap, bounce, pour a chemical in the port, stick a light in, they all pull up to 20" vac with a hand pump and no spring, why guess
Tom
Yeah. I have one. I just don't like wasting time I am not getting paid for. If I bounce the valve, give a quick look see, and see no light, I know concentricity is good, and WILL max my vaccum gauge. Then bump with a finish stone and the seat looks like chrome, I know it's as good as possible. No need to do 3 more steps I am not being paid for. No need to check with all that. I should clarify, it WILL max the gauge after the bump with a stone. Gaurenteed, without a doubt, 100% of the time. Why take 2 more steps. And yes, no springs, LIGHTLY setting the valve on the seat and not smacking it like I see a lot of guys do. And if it doesn't MAX your vaccum gauge out, not pull at least 20 inches, it's leaking, period

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Re: "Light tight" valve jobs

Post by zums » Thu Jun 14, 2018 8:26 pm

Frankshaft wrote:
Thu Jun 14, 2018 7:59 pm
zums wrote:
Thu Jun 14, 2018 7:48 pm
No one believes in accurate concentricity gages any more? , when i check a seat and valve face in v blocks and they are within spec i dont need to lap, bounce, pour a chemical in the port, stick a light in, they all pull up to 20" vac with a hand pump and no spring, why guess
Tom
Yeah. I have one. I just don't like wasting time I am not getting paid for. If I bounce the valve, give a quick look see, and see no light, I know concentricity is good, and WILL max my vaccum gauge. Then bump with a finish stone and the seat looks like chrome, I know it's as good as possible. No need to do 3 more steps I am not being paid for. No need to check with all that. I should clarify, it WILL max the gauge after the bump with a stone. Gaurenteed, without a doubt, 100% of the time. Why take 2 more steps. And yes, no springs, LIGHTLY setting the valve on the seat and not smacking it like I see a lot of guys do. And if it doesn't MAX your vaccum gauge out, not pull at least 20 inches, it's leaking, period
Far out,,, but if you have a leaker , is it the valve or the seat , your back to v blocks and gage , so which is a waste of time
Tom

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Re: "Light tight" valve jobs

Post by Frankshaft » Fri Jun 15, 2018 9:55 am

zums wrote:
Thu Jun 14, 2018 8:26 pm
Frankshaft wrote:
Thu Jun 14, 2018 7:59 pm
zums wrote:
Thu Jun 14, 2018 7:48 pm
No one believes in accurate concentricity gages any more? , when i check a seat and valve face in v blocks and they are within spec i dont need to lap, bounce, pour a chemical in the port, stick a light in, they all pull up to 20" vac with a hand pump and no spring, why guess
Tom
Yeah. I have one. I just don't like wasting time I am not getting paid for. If I bounce the valve, give a quick look see, and see no light, I know concentricity is good, and WILL max my vaccum gauge. Then bump with a finish stone and the seat looks like chrome, I know it's as good as possible. No need to do 3 more steps I am not being paid for. No need to check with all that. I should clarify, it WILL max the gauge after the bump with a stone. Gaurenteed, without a doubt, 100% of the time. Why take 2 more steps. And yes, no springs, LIGHTLY setting the valve on the seat and not smacking it like I see a lot of guys do. And if it doesn't MAX your vaccum gauge out, not pull at least 20 inches, it's leaking, period
Far out,,, but if you have a leaker , is it the valve or the seat , your back to v blocks and gage , so which is a waste of time
Tom
Well, all you have to do, is look in the port, turn the valve a little, look again, turn a little, look again, if you see light when the valve is on one spot vs the other, its the valve. If you see light the whole time you turn in the same spot, its the seat. But, the light bump with the finish stone, told you if the seat was dead on or not. V blocks work too. When I grind valves. I have a magnetic base on my valve grinder, with an indicator. I place indicator on stem, check for straightness. I then grind valve. I then put indicator on seat, it will show the runout. Since you already verified the stem was straight, and or running true, I have a lacey Williams accu chuck in my Kwik Way valve grinder, sometimes the collet doesn't seat perfect, checking to verify it runs true, takes 2 seconds, the seat to stem is dead on if the indicator says it is. The only thing I am really not verifying, is the valve tip. I know from checking, and but grinding, an un countable number of valves, I know it squares it dead on. So, I am actually checking all that in a different way. It does save time.

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Re: "Light tight" valve jobs

Post by KnightEngines » Fri Jun 15, 2018 10:17 am

I gotta agree with Frankshaft.
If you bump the seat with a stone & it cleans up straight away then it's good.
If the valve bounces nice then you are within guide clearance for concentricity of both valve and seat.
Vac test will be good provided surface finish is good.
Why waste more time confirming what you already know?

For non-professionals it may seem blase' but once you've done it 1000 times you really don't need to over think it.

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Re: "Light tight" valve jobs

Post by gofaster » Fri Jun 15, 2018 10:56 am

CJ just a question about a light clap of the valve to the seat for a impression,isn’t the valves working harder than that when the engine is running I mean when the valve closes with 150 to 450# of seat pressure seems you should be able to slap the valve down harder to see the impression.Just a thought?
The spring pressure can bend the valve stem far enough to seat, but...

Did you ever bend a piece of metal back and forth to break it?

In a running engine if the valve isn't seating squarely, it is getting bent by the valve springs to conform to the seat.

In a very minor misalignment things may wear in after time and run okay, if you're lucky.

In many cases the valve stem bends enough times to break at the valve head.
Jim McMahon
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