The valvespring is the curse of the overhead-valve, pushrod V-8. Racers and savvy enthusiasts have long been conscious of the effects of valvesprings going away. Take a cruise through the pits of any drag race, and you'll see there is a lot of effort placed on valvespring health. The same holds true for your street-driven Corvette engine, especially if it spends a lot of time sitting idle.
Of course, you might think this has little to do with your car, but that's contrary to the truth. Remember when the engine in your Corvette was fresh? It easily wrapped the tach needle over to the redline when you mashed the gas pedal to the floor. Over a period of time, the tach began to get "lazy" and, in worst cases, would occasionally pop and bang well short of the limit. Oh, sure, the noises and lack of brute power at the "big end" could be blamed on a poor carburetor tune-up, electrical woes, carbon buildup, or other gremlins, but 9 times out of 10, the culprit is tired valvesprings.
Selecting The SpringsNaturally, upgrading to a stiffer aftermarket spring has its merits (the new technology is tremendous; if stock parts aren't an absolute requirement, check out the new-technology valvesprings offered by Comp Cams, Crane, and Lunati). But there are some things you can do to a stock set of factory springs to improve their longevity.
The first order of business is to select the right spring. As an example, we'll use my previous (and long gone) L88 Corvette engine for a guinea pig. That particular combination was stock-appearing, but had been prepped for a bit of high-performance use. As a result, the engine was a mix of some aftermarket components (mostly inexpensive "cheater" stuff) along with stock Chevrolet L88 and ZL1 odds and ends. For all intents and purposes, the engine looked dead stock. Of course, valvesprings were a concern. Look at the facts and figures, and use the mathematical concept in your own Corvette.
Our camshaft featured the following gross valve-lift figures:* Intake: 0.5865 inch* Exhaust: 0.6300 inch
The valvespring specifics were as follows:* Installed height: 1.880 inch* Solid height: 1.100 inch* Outside diameter: 1.487 inch* Seat pressure: 116 pounds at installed height* Open pressure: 310 pounds at 0.560-inch valve lift
Now for some math. Without taking valve lash into consideration, the "available" spring works out like this:
Available Spring: Installed Height minus Solid Height1.880 inch - 1.100 inch = 0.780 inch
Net Intake: Available Spring minus Maximum Intake Lift0.780 inch - 0.5865 inch = 0.1935 inch
Net Exhaust: Available Spring minus Maximum Exhaust Lift0.780 inch - 0.6300 inch = 0.150 inch
As you can see, this combination has some fudge-factor built in. We have available room for added spring shims, spring seats (required with aluminum heads), and further adjustment. Unfortunately, that might not be the case with all combinations. Check your numbers carefully before taking drastic measures such as shimming the spring for more pressure or swapping in a different aftermarket spring (especially one that features a longer length or shorter stack/solid height).
The Stress FactorThere are other things you can do to improve spring life. One easy step is to pre-stress new valvesprings prior to installation. In other words, the springs are installed in a soft-jaw vise and compressed several times before installation. The idea isn't to "kill" the spring in a vise. Instead, compress it gently without physically stacking the spring into coil bind (watch the spring carefully as you compress it). The spring is then installed in the engine and the seat pressure is checked. If the spring fails miserably, it gets filed (or returned to the manufacturer) and a new unit is installed. By the way, if you don't have access to a soft-jaw vise, stack some paper notepads on each vise jaw. The thick paper keeps the valvesprings from being marred by the steel jaws.
Also inspect the spring, inner spring, and damper carefully. You might find that some OEM valvesprings have added "flashing" on the spring ends (this is quite common on some dampers). If that's the case with your spring(s), use a small die-grinder and carefully smooth over the burrs. After installing the springs on the cylinder heads, examine the relationship between the inner spring and damper to both the cylinder-head seat and valvespring retainer. Due to different designs in springs, retainers, and spring seats, there might be coil bind at these locations, but no coil bind on the outer spring. Look closely as the engine is turned through a cycle (by hand).
Routine MaintenanceAnother trick is to regularly check the springs using a seat-pressure tester (inexpensive models such as the Moroso unit shown in the accompanying photo are readily available). These testers simply slip over the rocker arm. Add a bit of muscle power and pull down on the tester. The number that appears on the beam scale (it's much like a beam torque wrench) is the spring seat pressure. If the seat pressure is down from specs, you can bet your boots the valvesprings are tired. By the way, we make it a practice to check the spring seat pressure every time the valves are lashed. The checking process adds roughly 15 minutes to the routine maintenance schedule.
When it comes to valvesprings, remember that more radical camshaft profiles eat springs faster than gentle profiles. In addition, buzzing the engine past the appropriate redline also has a decided negative effect on springs. Keep these things in mind if your Corvette doesn't seem as muscular as it once was.