Valve springs

[rocketracer380]

On a race engine is backing off the springs required for longer spring life I have a 15 degree sbc 440 with about .880” lift never backed off valves broke a few springs after about two years never made a pass with this engine

[engineguyBill]

If the engine is not going to be run for an extended time (i.e. four months or more), I always back off the rocker arms during this time. Your springs will last much longer . . . . . .

[allencr267]

never made a pass with this engine

What did it do, also, what was it last doing?
Sitting under 880 minus lash for a while must be much more uncomfortable then a car's full-time suspension springs.

[MadBill]

I'd like to hear from anyone who removes his OHCs for the off season...

[Alaskaracer]

I've never backed mine off and have never seen a change at all in spring life, seat pressure, or open pressure....only time I've seen a change is after running them most of the season........

[Kevin Johnson]

https://www.ideals.illinois.edu/bitstre ... sAllowed=y

localized stress.jpg

By tempering quenched steel, it becomes less brittle and more ductile without sacrificing too much hardness. ...

The spring exists on a continuum of ductility versus brittleness, i.e. it contains elements of both qualities (in reference to the Dolan citation).

Leaving the springs under static compression/tension for extended periods of time might simply identify and aggravate stress raisers that would have emerged later in the service life. It is possible, though unlikely under proper storage, that corrosion creates stress raisers that are then stressed under static loading.

[David Redszus]

The metal used to make a valve spring has a specific tensile strength which is expressed in units
of pounds per square inch. Since the tensile values are often quite high (150,000-175,000psi), the
unit Ksi (150Ksi) is often used.

When a spring is compressed, a stress is imposed upon the spring, which is increased with increased
deflection. As long as the imposed stress does not exceed the tensile limit of the material, no change
in length will occur.

In an engine, increased valve lift will increase valve spring stress. The spring stress on a closed valve is well
below its tensile limit. But the spring stress imposed by a valve at maximum lift may well exceed its
tensile limit. Over time the spring will sag and lose free length requiring the use of a shim to restore its original
free length and seat/nose force. The spring rate will not change

[MadBill]

The metal used to make a valve spring has a specific tensile strength which is expressed in units
of pounds per square inch. Since the tensile values are often quite high (150,000-175,000psi), the
unit Ksi (150Ksi) is often used...

David, your usage of the word 'tensile' corresponds with Yield Strength rather than Ultimate Tensile Strength.

Also, surely a spring compressed to/beyond its yield point at max lift every other cycle would quickly lose free height and load capacity? An example of the inverse is the set of Isky Tool Room springs a friend of mine bought used for $50 and ran for five years in an 8,000 RPM road race SBF. When he finally changed them out last winter they ranged between 0 to -10# of the seat load when he installed them.

[digger]

Springs stressed past yield are not going to last many cycles

[ptuomov]

And I think that valve springs that are matched for the application really only start losing load when they overheat.

[tenxal]

We don't back the valves off on any of our drag race stuff in the off season...no issues at all. In fact, given the 'dry' characteristics of some of the race fuels (C11, C12), frequently rotating the engine to stay ahead of any sticky guide issues is a plus.

[David Redszus]

Springs stressed past yield are not going to last many cycles

Good point.

We can compress a spring to coil bind and it will return to its original free length provided we stay in its elastic range and
not venture into its plastic domain. Proper spring design is required to accomplish this.

Ferrous materials have a finite cycles to failure limit. If load reversal is added, the number of cycles is greatly reduced.
Some engine builders will log engine hours of operation to determine the number of load cycles and schedule spring replacement.

[Kevin Johnson]

We don't back the valves off on any of our drag race stuff in the off season...no issues at all. In fact, given the 'dry' characteristics of some of the race fuels (C11, C12), frequently rotating the engine to stay ahead of any sticky guide issues is a plus.

Good idea.

[digger]

i back off my rod bolts to.

[swampbuggy]

^^^^^^^^ seriously, or is that a joke ??? Mark H.