how critical is installed valve spring height?

[PRHeads]

I measured anywhere from 1.825" to 1.844" using a Proform valve spring height micrometer.

To be fair, this isn’t terrible.
It’s 1.835, +/- .010”.

 

[PRHeads]

Forgive my lack of experience but....
If a shop installed valve seats, is it possible that the taller seats result in a shorter installed spring height? Are the back sides of different valves thicker in some cases? I would assume that these would be machined to get the valve stem height all the same but I don't know the ins and outs of head machine work.

I’d be very surprised if any valve seats were actually “replaced”.

Who’s to say the IH discrepancy isn’t from a variation in valve margin thickness or the spring seat depths.

 

[copper67sat]

Just be aware that there is no “industry standard” for retainer installed heights.
So, the Hughes +.100” retainers may or may not actually be +.100” compared to the Stealth retainers.

Didn't think about the lack of a standard but that's the next set of measurements I am planning to take - just change to the new retainer & locks. That will confirm the shims needed.

 

[copper67sat]

The invoice from the shop says "Blend chambers to valve job. Seats were never installed correctly from manufacture." Interpret however you want. I don't know what to believe from them anymore.

 

[PRHeads]

If there isn’t a charge to R&R some seats, you can be pretty sure it didn’t happen.

It’s not uncommon on those heads to have some of the exhaust seats sitting “proud” in the chamber.
I’ve seen it on BBM rpm heads as well.

 

[copper67sat]

If there isn’t a charge to R&R some seats, you can be pretty sure it didn’t happen.

It’s not uncommon on those heads to have some of the exhaust seats sitting “proud” in the chamber.
I’ve seen it on BBM rpm heads as well.

Not seeing R&R seats on the invoice so you're probably right. I just wish they would have said something about what they found while they still had the parts.

 

[rickseeman]

Sometimes you can find .050" retainers or maybe that was keepers?

 

[PRHeads]

Here’s a pic of a cnc stealth chamber.
On this particular one the exhaust seat is just barely sitting proud in the chamber, but they can be sticking out way way more than this.
If yours were like that, there should be evidence of where they addressed it somehow, since there is a mention of blending.

Unless it’s real bad, I just leave it.
And even when I do address it, I just put a chamfer on the outer edge.

 

[nitro_rat]

Forgive my lack of experience but....
If a shop installed valve seats, is it possible that the taller seats result in a shorter installed spring height? Are the back sides of different valves thicker in some cases? I would assume that these would be machined to get the valve stem height all the same but I don't know the ins and outs of head machine work.

Yes, there are so many interfaces in a single valve/seat/spring set that it will drive you mad trying to set up a pair of heads the same. Every cut on the valve face and seat face raise the spring and stem height. If you change the seat that will change the spring and stem height. Once you have the valve face and seat set the way you want, then you have to get all the spring heights equalized to whatever number that is supposed to be. Then once all that is done all of the valve heads need to be the same height, especially on a Mopar with a shaft mounted, non-adjustable rocker setup. They can kinda be all willy-nilly on a small-block Chevy with individual rocker arms that are adjustable. They really need to be the same on a Mopar or every valve will have its own lash and lift when compared to all the others.

What this really means is, that unless you have a "head shop" machine that can set all new seats in at the same height, you have to do A LOT of careful measuring before, during, and after tear down. Then you have to keep track of all of the cuts you make, compensating where you can to equalize everything as closely as possible. You have to be meticulous at your machine work, and diligent in your measurements and assembly. You'll still probably have to make compensating cuts on the tips of all the valves to get them just so, so they're all the same height in the end.

Most production shops can't be bothered with that level of precision, and if they can be, I can't afford to pay them to. Luckily I fell into my own little Sioux valve and seat machine set up and a few other cylinder head specialty tools. I take my time and set up my own when I need to.

 

[copper67sat]

I looked around and didn't find many options for BB Mopar but maybe I should have just looked for 1.500" retainers and/or 7 deg, single groove locks for 11/32 valve stems.

 

[PRHeads]

The way the valve seats are cut on the non-cnc heads, they’re “small”. Meaning the point of contact on the valve is way on the inside of the seating surface of the valve.
When I recut the intake seats, I move the point of contact to the outside. This does three things……… it lets me add a second angle below the 45, which improves the transition into the bowl, and leaves space on the valve for a back cut, and slightly lowers the valve into the seat, which adds a touch of installed height.
The exhaust seat cutter has a radius below the 45, but the contact point is also moved out towards the edge.

If I think of it, next time I get a set of ootb stealths to prep, I’ll see if I can get a before/after IH comparison between the as delivered VJ vs after the seats get recut.

Ootb valve job- lapped in to illustrate point of contact:

 

[PRHeads]

I looked around and didn't find many options for BB Mopar but maybe I should have just looked for 1.500" retainers and/or 7 deg, single groove locks for 11/32 valve stems.

Hughes might know how his +.100 retainers compare, height wise, to the stealths.
You don’t need the full .100……. .040 or so would get you there.

 

[PRHeads]

I’ll add this to the discussion……..
I have a set of new stealth springs here taken off a set of heads that got a spring upgrade.
I just checked one at 1.83……. 145lbs, and 325@.500 lift.

Just pointing out that as the heads came back from the machine shop, they had spring loads very similar to what you’re shooting for.