I have heard all kinds of numbers for a reasonable
safe margin for valvesprings. The most common is
0.050", but there must be a lot of other factors.

The LT4 hot cam and springs only has 0.035", so
what is the right minimum number that provides a
safe margin from coil bind?

 

I can't believe that none of you has an opinion
regarding the safe minimum margin for a valve
spring.

Come on now.......give it up.

And yes, I did a search, but there are tons of
posts regarding springs but very little about
recommended safe margin for clearance.

 

I wouldn't try to use that measurement. I would use the spring manufacutuer's recommendations regarding max. lift on cam.

 

The correct setting should be based on several factors
including installed height, closed height, and lift at the
valve. Assuming you do not coil bind at your max lift, the
installed height minus closed height minus the lift will
leave you with your margin. Example for Hot cam:

1.78 - 1.22 - .525 = .035

For my setup with the Crane 227 and Isky 235-D springs
installed at 1.75 (recommended) height it would be:

1.75 - 1.15 - .552 = .048 (less than .050)

I have talked to Isky and the 235-D can be installed at
more than 1.75 and up to 1.78 is fine. So, should I install
the springs at 1.76, or 1.77 to increase the margin to at
least .050?

 

You correctly state that there are a number of varibles that must be considered to correctly set up springs for max performance and life. Spring pressure at open and closed at the selected height is critical also. You should include the spring pressures in your consideration of determining installed height.

Comp Cams website site has a great tutorial section on the valve train. It sounds like you have some theory down, but have not done this much before. The more info you get the better.

If your spring pressure is adequate for your needs at 1.77, then do it. I doubt you'll see much difference between 1.76 and 1.77 and heck you may not be able to achieve that perfectly anyway since shims come in .015" increments and each valve seat/pocket has it's slight variances. Just be careful to get the valves on any one cylinder as close to each other as possible.

Do you have a barrel micromenter to establish the correct goal height on each sping? If not get one; it is necessary.

 

Agree with the previous post. To elaborate on one point: it's difficult to even measure 0.002" unless you have a barrel mic. I'd also like to see 0.050" minimum to avoid any possibility of coil bind. But I am conservative, especially when it comes to my motor of which I have only one!

Rich Krause

 

Don 97 SS: I have a barrel mic and a set of
shims. I was wondering how you could even achieve
exact installed heights when the shims are 1.5 times
the thickness of the desired increment (.010). So if
it's not possible to achieve 1.77 across the board it's
most important to have each cylinder equal? Like #1
at 1.765I and 1.765E and #2 at 1.77I and 1.77E, etc.

rskrause: Thanks for the feedback on the
.050. I thought that was a reasonable minimum. Which
means that I do not want to go with 1.75 installed
height.


For the Isky 235-D the spring is rated at 350 #/in. or
3.5# per .01 inch and 130# at 1.75 installed height.
The pressure at 1.76, 1.77 and 1.78 would be 126.5,
123 and 119.5 respectively.

What is the maximum deviation that is reasonable
between cylinders? Is +-.005 OK, or even doable?

I have no idea if it's needed but I also bought a set
of +.050 keepers in addition to the regular ones. I
will use the L98 spring seats/locators with the Isky
springs and did not know if they are thicker than the
stock ones. Anything I should know good/bad regarding
the +.050 keepers?

Another thing I am assuming is that my KD sytle
spring compressor will work with the Isky springs
which have a damper. The work will be done with
heads on the car.

 

I agree with the above posts but would add that you shouldn't forget about ensuring clearance between the retainer and valve stem seal. The recommendations for this clearance are made very clear at the Crane and Comp cams tutorials that are listed above.

 

I've used a KD spring compressor. It is o.k., but does NOT work well with dual springs or with a damper. I would highly recommend the Moroso stud mount compressor for about $80. Do a search on this as the topic comes up often. This compressor is the best I've seen and will make the job much more easier and less aggravating. Moroso

The only reason you would need plus or minus sized locks is if you have trouble getting to the correct height needed. I can't say if you need those on not. Did someone advise that you needed them? The L98 sping seats are probably .060" thick from my recollection.

 

I measured a L98 seat but can't remember the dimension. I
can check it again. For some reason I thought the stock seats
were thinner, which may not be true. The locks were only $20
so even if I don't use them it's better to have them and not
need them to not have them.

I also have a stud type spring compressor but did not think it
would work in the back on #7 and #8. Thanks again for the info.

 

My Moroso spring compressor worked on the back two cylinders. However, I hand to disassemble the tool and install it over the stud. It was tight but worked under the cowl.

The K&D spring compressor is difficult to use with dual springs due to it's "fingers" being too short to grab both springs very well.