Testing valve springs

[SigmundF]

Hi,

I have a spring tester, measuring lb per square inch, but all the references I can find for testing/measuring the springs are in lbs. And as far as I how it is not possible to convert lb per square inch to lbs (pressure versus weight). Could anyone help me with the spec. for valve springs in lb per square inch or PSI

[MatthewBrum]

Are you sure the spring tester is not lbf/in instead of lbf/in^2? The spring rate is usually measured in lbf/in. If your spring tester uses some sort of pneumatic or hydraulic cylinder pressure then you have to multiple the area of the cylinder with the pressure.

[911pcars]

AFAIK, it's the same (or they labeled it incorrectly). A spring tester doesn't know the OD of the spring being tested (and thus the lbs/sq. in. calculation), or perhaps the test plunger is 1" square. Most spring testers measure the force in pounds (US), kilograms (Metric) or fractions or multiples thereof. Squeeze the spring to the compressed height specified by the manufacturer, then observe the display.

Spring testers that measure extension springs work the same way. For the most part, the shape or type of extension spring doesn't matter.

Sherwood

[SigmundF]

I looked at the tester again last night and the tester show PSI and kg/cm^2...

PSI = Pound per square inch, maybe it is labeled incorrect. I agree that the tester do not know OD of the spring tested

Does anyone have spec. for the valve springs?

Here is a picture of a similar tester...

[HawgRyder]

Valve springs are strange animals.
One moment they are right on spec...and the next, they go "soft".
With race engines, you can hear the difference, one moment the engine is crisp and tight... and then it loses RPM at the top end and does not sound correct.
So....if in doubt...replace them.
Springs are not the most expensive parts you will buy, and good ones are worth the price.
I have used Vasco-Jet springs in avery engine I have built over the years....more expensive....but they do perform very well.
Normal springs roll off on pressure slightly after a while...then stay at that pressure for a long time...then roll off again to the weak spot.
Vasco-Jet are different....they start at one pressure....increase slightly for a long time....then break!
The trick is to replace them at the correct time.
And...when you test springs....test at the set height (valve closed)...then at the open height (closed plus lift of cam).
I have found many springs that will pass the open valve number....but not the closed number...it has something to do with dynamic range of material used in the spring.
Have fun
Bob

[racing97]

Valve springs for the most part are measure in force lbf but some stress calculations are registered in PSI, such as wire stress etc. What is it you need to know about your spring or the Porsche spring maybe we can help.

regards

[SigmundF]

Racing97

I want to check my valve springs (standard spring for a 2.7 CIS) but the spec I have found so far, is 280-300 lbs open for intake and 260-280 lbs open for exhaust.

But the tester I have measure in PSI (or maybe it is labelled incorrect and actually measure lbs, I am trying to get that verified.. ), so my question does anyone have the spec in PSI, so I can check the springs with my tester?

[HawgRyder]

It's early morning here and all my neurons have not woken up yet....LOL
Doesn't PSI stand for pounds per square inch?
So the guage you have reads in lbs....right?
Bob

[racing97]

Originally Posted by SigmundF

Racing97

I want to check my valve springs (standard spring for a 2.7 CIS) but the spec I have found so far, is 280-300 lbs open for intake and 260-280 lbs open for exhaust.

But the tester I have measure in PSI (or maybe it is labelled incorrect and actually measure lbs, I am trying to get that verified.. ), so my question does anyone have the spec in PSI, so I can check the springs with my tester?

Sigmund
I don't have the figures in front of me but the open pressure weather it be in psi or lbs is high for a stock spring. The spring rate is around 315 lbs (per inch) and full open before 1.25 mm coil bind is around 220lbs with a seat pressue of 70 lbs or so at 34.5mm installed height. What is of tantamont importence is that your springs are within 5% of one another at a equal amount of compression and that at full open you have 1.25mm clearence before the coils contact one another. If you need more info such as wire stress and frequency I will dig it up for you as I have already done the anaylsis just misplaced the papers.

regards

[chris_seven]

Sigmund,

Are you only going to measure the spring rate? I think that it would also be a good idea to measure the 'load at fitted length' as well.

I think you should aim to have all the springs you plan to use within 1% of the nominal value.

[SigmundF]

Thank's for the response...

I think some of the confusion can be related to my understanding of terms related to pound, I am used to metric...

"PSI" is Pounds per square inch, "lb" is pounds, what is "lbs" pounds in plural or pound per square inch?

So, when you refer to "lbs" is that weight og pressure?

[racing97]

Sigmund the units are the same pressure = wieght exerted

regards