Replacing Valve springs due to age?

How long do the valve springs typically keep their tension within serviceable limits?

They are almost 30 years old with 20k miles on them. Would I be ahead to replace them with some APE springs while I have the head off, or am worrying about something I don't need to be. I wish I had something to test the tension but I don't.

The head is going on my 810 build and I"m not planning on revving it past the redline. I'm going to be running the stock KZ750 cams and probably later upgrade to some GPz cams.

As always I appreciate the input. Thanks.

The longevity likely varies, but FSM should provide the valve spring tolerances for both tension and squareness.

Am thinking 20,000 miles would show minimal if any valve spring deterioration.

Don't know what if any adverse effect might result from long term storage where valve stood open.

Good Fortune!

The machinists checked the springs on my KZ750 head at rebuild (75k miles, 30 years age) and said they all read good to new spec. He said they were easily good for 10K RPM but the rest of the engine is not.

Well with the Build your doing, and the cost of Quality Springs For the Cam you "Will" run, I would put springs in. Well worth the peace of mind, when your all set up and running the guts out of it, you won't be wondering where the old springs Might Float. With the Increased lift and duration, your piston to valve clearance will be less, and with the power band moved up the range, you will be seeing a higher average RPM, valve springs make a lot of heat as well I'd change them.

For a stock motor and general cruising around town stock old springs are fine. For any performance work and aggressive riding new springs are a must.