allowed valve spring tension loss

[dwilliams]

Absent any hard recommendation from the spring manufacturer, what percentage of seat pressure loss should I use to determine when the springs should be replaced?

[bigjoe1]

I will give you an example of some real quality springs--PAC 1324----275 seat---810at 850 lift--after four years on drag racing---280 seat--- 810 at 850 --- ABSOLULY UNBELIEVEABLE ! 8500 RPM twice on every run== You must realize that lots of this is because I run a very stable camshaft grind= I could not believe it myself




JOE SHERMAN RACING

[cgarb]

Is that a mistake? How does a spring gain 5lbs on the seat after being run for 4 years? I have seen a set of Isky toolroom springs hold up pretty well after a few seasons of racing. The lobe profile has some to do with it, having the right spring for the application and having good oil flow to cool the springs too. Oh, and a driver with some brains don't hurt either...lol.

[hoodeng]

As Big Joe has pointed out ,good quality springs give good service ,but i would imagine he checks them regularly for any sign of pressure loss.
In race motors the springs [in our instance] would have been changed if the seat pressure loss was 10-15 lb off an installed seat pressure of 400 lb.
In street use springs that were installed at 180 lb and show a loss of 10-15 lb over a service life of the engine would be shimmed back to 180 lb,but only if they are known brand name springs that had a no fail history.
Any doubt would require replacement of the set.

Cheers.

[dwilliams]

Given their rep here, if PAC made springs to fit all the weirdball engines I build, I'd use them in everything.

Until they do, I'd like to keep a suspicious eyeball on the lesser brands.

[engineguyBill]

Wow, MORE spring tension after four years of severe use? Have never seen that. Did you use the same spring tester and procedures both times, Joe?

As valve springs get older they will (generally) begin to lose some some tension and need to be replaced when the tension falls below the recommendations of your cam manufacturer. When testing valve springs, all of the springs in a set should show a consistent reduction in tension throughout the set. If one or more of the springs shows significantly more tension loss than the rest of the springs in the set, that is a red flag and all of the springs should be replaced.

[bigjoe1]

I will admit, I did NOT do the testing on the springs after all those runs--- BUT, even if it was still the same, it is very impressive
P S -- I do spot check the springs every once in a while.


JOE SHERMAN RACING

[PackardV8]

FWIW, Joes' numbers are within the normal variables of a manual bench valve spring tester, much less the version which measures on the engine. 5# on a 275# spring is 1.8%. It's difficult to reset the height scale to within 1.8% of .850" two times in a row when just running springs to confirm they're not yet in the failure mode.

Yes, some use a digital version of the bench tester and some set their analog tester with a micrometer, but 5# is not a real number until the same operator has tested the same springs on the same machine, set with the same standard.

[RCJ]

I used 20lbs starting at 260 on the seat.After 600 laps in a dirt late I removed them.The springs had lost very little,I was getting wear on the seat and the installed height had grown.

[hoodeng]

Using the same tester for some is not always possible ,but if you were in a level of competition that requires the nit picking detail of consistency ,the necessity of using the same tester is paramount. I use a Rimac digital probably every week and regularly check it with the Crane 99851-1 calibration spring ,so i can pretty much trust the readouts,[ i know there are a lot of other good brands of testers other than the one i use] .
In a track situation a Jesel [Logan-Smith type] on vehicle tester was used between rounds ,you could see the relationship between engine performance and spring pressure on the data ,if your tune was pretty right and the engine wasn't spooling up on pace in the top RPM range, check the springs first.

Cheers,