valve spring tension

S

Seabees

Senior Member
Howdy boys, I have a question for you "Experts"! In Les' book, he states valve spring tension should be 60lbs (+/-3) at 2.5" compression. At 2.75" compression it should be 36lbs. After speaking with Joe at Snyders, wondering why the new sets I bought tested at 40lbs at 2.5", he informed me that the original Ford specs calls for 40lbs. I called my good buddy Jim Brierley, who has built more engines than I ever hope to, and asked him what he thought. His figures say at 2.375", the compression pressure should be 38-40lbs. So, what is Les referring to when he is stating the spring tension at 2.5" compression should be 60lbs? I did try to call Les, but no answer. I left a message. I'm sure he's a very busy guy, which I understand. Thought I'd put the question to you guys. OK engine builders, what say you?
 
To do it correctly, you need a spring checker..!

1. New springs will loose about 10# in just running them for the first time..
2. Install the valve with the retainer (NO spring) and measure too a 1/64"..
3. Then check the spring in the checker and shim too that height, what ever pressure that
you need / want..

I've used this method for OVER 55 years...it works every time. Remember this,..the
lifter and valve NEEDS to follow the cam lobe, too run properly..
 
Thanks D.J. No. 2 in your answer is a bit confusing to me. What am I measuring? I do have a "spring checker". That's why I know the springs I have are 40lbs at 2.5" compression. Again, my question is, what compression pressure should they be at 2.5" compression? 60? 40? Thanks.
 
Boy, you guys put a lot more thought and worry into this stuff than I do. If my engine is otherwise majorly rebuilt by respected people and sources, (new babbit, rings, pistons, valves, seats and guides, etc.,) I buy new springs from Snyder’s or Bratton’s, install ‘em, set clearances, and go. That’s been my Modus Operandi for over fifty years with no problems involving spring pressure. The spring’s job is to return the valve to the cam. If it doesn’t do that, it’s more likely to be a sticky valve due to bad guide, a bent valve (very rare), or a broken spring, or something else, but not spring pressure. 60#? 40#? I don’t know and don’t care and never have. Sometimes too much information creates unnecessary problems, and sometimes ignorance is bliss. :cool:
 
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This came up once before in this thread. They didn't really get to a conclusion, but they did establish that 40 lbs @ 2.375" was quite common among springs that were tested. No one was sure where Les got those numbers. Something that tends to muddy the waters further is that the standard one-piece replacement valve guides lack a shoulder, which alters the installed length of the springs and thus their operating pressure. Some folks compensate by adding shims/spacers, while others compensate by changing to stiffer springs.
 
Seabees said:
Thanks D.J. No. 2 in your answer is a bit confusing to me. What am I measuring? I do have a "spring checker". That's why I know the springs I have are 40lbs at 2.5" compression. Again, my question is, what compression pressure should they be at 2.5" compression? 60? 40? Thanks.
Click to expand...

You are measuring the "installed height" of the valve stem and the retainer.
With that figure you measure the spring, in your spring checker, and that will
give you the spring pressure with the valve closed. This is done with the valve
in the block / head...make sense now...?
 
To add more context to D.J.'s reply, the central idea with the spring pressure is that the spring needs to clamp the valve face to the seat when the valve is fully closed – both to keep it from leaking and to facilitate the sinking of heat from the valve into the block. There's a certain target pressure needed to do that.

You need to make sure your spring will deliver that target pressure at a certain length. That length is the "installed height," the total distance between the ends of the spring when it's installed in the valve chamber. It'll be pressing against the retainer at the bottom, and against either the shoulder of the valve guide or the block itself, depending on the type of valve guides you have. This variability is why you should take the length to be tested from your actual engine instead of from a book.
 
Spring rate and installed spring height are two different things.

Seabee' is asking why he has two different spring rates and specs.

Les' specification is more than likely for the "V8" spring, which is a common performance upgrade to the Model "A" springs.

J
 
I am 100% on board with 700's post#4. I have never given thought to spring tension. Buy the spring and install. But, I am sure checking tension is the correct way.

Now you guys want me to buy a bathroom scale and a drill press. Next thing you will ask me to check MY weight.. GEEEEZ.:p
 
Ok guys, now we're getting somewhere. Thank you Mr. Nelson! It looks to me that, 40# on my spring checker, at 2.5 inches, is where I want to be. And thanks to you also, D. J. and Alexiskai, I will check the installed height and see what I get. My biggest concern with all of this is of course, I don't want to have to pull the damn apart again! Although, each time I do, it's a new learning experience! Thanks guys, I appreciate the help. I'll let you know how it turns out. It appears this engine has gotten hot at some point in it's long life, and the springs are what I feel are the problems with it running correctly. Yeah, I've check the carb and dist, numerous times. It ain't that! Timing gear is fine also. I'll keep you posted.
 
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