Valvetrain Repair - Fixing Valve Float

When he spotted the problem of valve float, Troutman immediately guessed a couple of possible reasons for the problem. But because the valves didn't show any signs of float when the engine was originally built and dyno'd, the most likely culprit was simply worn-out springs. That is easily detected by checking the spring pressures against the rated pressures when they were installed. Troutman's records indicated that when the engine was built, the Comp springs were rated at 160 pounds on the seat and 340 over the nose with a 1.760-inch installed height. Peak valve lift is 0.485 inch, which is well within the springs' range, safely managing 0.530 lift before going into coil-bind.

On the scale, it quickly became obvious that these valvesprings had been raced far too long. Troutman checked several springs, and the average seat pressure had dropped 40 pounds to 120, and the spring pressure at max valve lift (over the nose of the cam lobe) dropped approximately 90 pounds to 250. Normally, new springs will drop 5 to 10 percent of their total spring pressure from breaking in, but these amounts are indicative of springs that are worn out.

It turns out that the springs had been run all season, and they probably should have been changed around midseason. There was no fault with the springs. The combination of a strong cam lobe and high rpm levels meant the useful spring life was limited. Buying a new set of valvesprings midseason may be tough to swallow for some race teams. However, in this instance, the investment of a new set of springs would have been worth it because new springs, valves, and retainers must now be purchased. In addition, touching up the valve seats in the combustion chambers is necessary at almost every rebuild, but valve float can be so harsh that the hardened seat inserts must also be replaced. In the long run, it would have been much cheaper for this racer to purchase an extra set of springs.

The best way to avoid the damage of valve float caused by worn-out valvesprings is to check spring pressures regularly. On-head spring pressure testers can be purchased for anywhere between $75 and $250 and should be in the toolbox of every race team. It doesn't matter if your spring tester finds the same rates as your engine builder's spec sheet. Simply check the rate of the springs when the engine is new. After a couple of races, the springs will drop approximately 5 to 10 percent of their original pressure and then stabilize. Log your pressures and check a handful of your springs randomly after every second race (or more often if you are running long races). The springs' pressures should be the same within a pound or two. Once the pressures begin dropping again, you can be confident it's time to replace the springs. Sometimes you will have only one spring go bad, but they will most often begin failing as a group.

If valve float is a problem, even with fresh valvesprings, Troutman says there are other options available to you. Generally, you must try to change one or more of the components of the triangle we talked about earlier: valvetrain component weight, spring pressure, and rpm levels. The most common solution is to simply raise the spring pressures. Often, however, that isn't an option because the rules limit the types of springs you can use. The next option is to limit valvetrain component weight. If you're running steel retainers and titanium is allowed, you may have to invest in a set of titanium retainers.

Troutman also recommends always running the shortest valve stem and pushrod combination possible that still allows you to achieve maximum valve lift without getting into coil-bind. Any extra valve stem length is just extra weight you have to move up and down every time the valve is opened. Shaving 0.050 off the valve stems may not sound like much, but every gram of weight saved helps. Finally, when all else fails, you may have to change your gearing to affect the rpm range the engine experiences on the track.

In all, valve float is something each and every one of us should be able to easily avoid. A little routine diagnosis of the springs coupled with proper component selection means that you should never experience a valve float problem.