Valve float/spring surge, what is it?

[Mr. Motorhead]

Understanding valve float in an engine has always been kind of a gray area with 36hp engines for most people, I found this explanation in another automotive forum that seemed pretty easy to understand. As we all know, the main limitations to any 25hp and 36hp engine is:
1.) Cylinder heads
2.) Valve train

I copied a snippit, here it is-

"Some Common Causes:
* Excessive engine speed leads to excessive valvetrain acceleration, and the valve springs may not be able to maintain contact between all the components. If you know the peak acceleration rate of your cam, and you know the force vs displacement profile for your valve spring, and you know the mass & inertia of your valvetrain components, you can calculate a kinematic separation cover factor that will tell you how fast you can run the engine without the mass x acceleration overcoming the spring force. This answer will always be wrong in real life, because...
* All of the valvetrain components, such as the pushrods, rockers, springs, etc., are flexible, and they will vibrate. Valvetrain vibration compounds the above, and significantly increases the required spring force to maintain contact between the valvetrain components.
* The valve springs themselves may resonate (vibrate quite a bit). This is called spring surge. Picture what happens if you hold a slinky outstreched, pinch some coils together, then release them. The compressional wave travels up and down the slinky. Spring surge is very similar. It increases stresses within the spring, and it reduces (periodically) the amount of force that the spring applies to the seat and retainer.
* Excessive valve lash compounds the above problems. Too little valve lash is worse, but for a different reason.

Some Remedies:
Valvetrain vibration:
* Lower mass valvetrain components
* Increased specific stiffness of valvetrain components
* Increased spring stiffness (add a helper spring if needed)
* Increased spring preload (add a helper spring if needed)
* Use a different cam profile (to excite less vibration)
* Reduce valve lash (to reduce impacts & excitation of vibes)
* Increase damping within the system
Spring surge:
* Replace the spring with a spring that has a higher surge frequency
* Use a different cam profile (to excite less vibration)
* Use concentric valve springs that rub against each other. The rubbing will remove energy and attenuate the spring surge. (this isn't the same thing as "cancelling the resonant frequency," because it reduces the vibratory magnitude at all frequencies vs the same spring pack without rubbing)
* Reduce the solid clearance of the valve spring, to increase coil clashing. Coil clashing removes energy and reduces the magnitude of the spring vibrations
* Add damping coils to the valve spring. Damping coils are coils that change the spring rate suddenly during a few mm of lift near the fitted length. Sometimes the damping coils are completely closed at the spring fitted length. The sudden change in spring rate breaks up the spring resonance as surge sets in."

http://www.automotiveforums.com/t152566-need_technical_explanation_of_valve_float.html

VW in their infinite wisdom did put dual springs on some but not all 25hp heads. I suspect it was to remedy a softer valve spring used on a 25hp. I know that stock springs have a free height of 43mm and are rated at 73 pounds. Are 25hp the same or softer? At any rate, the inner coil on the 25hp springs was serving to dampen the spring surge and not necessarily to increase pressure as the springs can be easily compressed with your thumb and forefinger. I was going to test this idea out with a set of OE inner 25hp springs and maybe have some made, but someone else already did it.

http://www.thesamba.com/vw/classifieds/detail.php?id=1608928

I bought a couple sets of inners to use, we'll see what they do.
_________________
30 years experience in the sales of new and used auto parts!
36 horsepower parts for sale at http://www.aircooledresearch.com/
Or the new site at http://www.bugparts.com
Check out the Bonneville project:
http://aircooledresearch.com/docs/thebonnevilleproject.html#

"All limitations are self imposed."
Some Chinese guy

[snowbug]

[Mr. Motorhead]

"the inner coil on the 25hp springs was serving to dampen the spring surge and not necessarily to increase pressure as the springs can be easily compressed with your thumb and forefinger"

So no, I think it will not add much in the way of seat pressure. I'm setting these up to run along with the HD springs I sell that do have a higher pressure rating at 88 pounds instead of the stock 73 pounds. 25hp and 36hp springs are both the same size, but my question is do the 25hp springs have the same poundage rating as 36hp? (I don't have any specs on that) Stock retainers are being used in all cases. I can't ever recall seeing a retainer failure on a 25hp/36hp engine. Failures are usually valve stem related that I have seen.
_________________
30 years experience in the sales of new and used auto parts!
36 horsepower parts for sale at http://www.aircooledresearch.com/
Or the new site at http://www.bugparts.com
Check out the Bonneville project:
http://aircooledresearch.com/docs/thebonnevilleproject.html#

"All limitations are self imposed."
Some Chinese guy

[snowbug]

[newps]

Hi Matt, I would like to say that I have had wolfsberg west spring retainers
de form on my 36hp, 1602 with you #2 cam and hd springs.
This was after a year of runs at Bonneville. I thank it is something you/me have to keep an eye on.