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Longer life for valve springs

valve-springsGetting valve springs to live in a World of Outlaws sprint car engine - one that is 408-410 cu in and makes 850 hp (with more than 700 lb-ft torque at 6300 rpm) - is one of engine building's black arts. At Shaver Specialties Racing Engines (SSRE) in Torrance, California, the challenge is to overcome the "voodoo of valve spring breakage," according to Dennis Hardesty, right-hand man to owner Ron Shaver.

"For the past year-and-a-half, the majority of our racing valve springs, retainers and spring seats are coming from PAC Racing Springs. The valve spring is a double spring with a damper insert," he says. "We use the same spring for both intake and exhaust applications because we have a bit more intake lift than exhaust lift over the nose (spring pressure)."

Buying an off-the-shelf part from PAC - or any other vendor - means building trust with the manufacturer. "Sometimes the manufacturer's suppliers don't always have the same metals, and there are some aspects in the making of a valve spring that are not totally under control," Hardesty says. "In manufacturing there can be some digressions (that can ultimately kill an engine)."

The current spring that Shaver uses for its World of Outlaws engines for four-time champion Donnie Schatz and his True Speed team, which is owned by NASCAR Sprint Cup star Tony Stewart, is distinguished by its raised seat. "Instead of the spring seat being flat, it's got a little bump. The normal 100-thousandths or so on the retainer is now shared by the retainer and the spring seat, so that takes a little weight out of it," Hardesty explains.

"The reason for using the lightweight steel retainers instead of titanium is our damper," he says. "The damper tends to tear up the titanium, so we were always having to replace the titanium. The steel ones, while more expensive, last three times as long."

On its state-of-the-art engines, SSRE requires rebuilds every ten to 12 races, or about 400 miles. "Valve springs are now seeing 20-24 races, and that's unheard of in this business," Hardesty says.

valve-springs spring-valves-retainers-clips

This 164 g PAC spring meets increased pressure over the nose from what Shaver's engine group used several years ago. "We used to run about 700 lb over the nose and now we're seeing about 800 lb of pressure," Hardesty explains.

"In sprint cars we see a lot of uncontrolled valve motions because they start slipping the tyres. A driver might be running 7500 rpm and something happens on the track - suddenly he goes to 8500! We've got to have some safety factor in these big parts."

Part of the reason for this incredible longevity is due to lighter weight of the intake valves, and the rest comes from the use of a 300M special retainer. Here, Hardesty says, "The half of the step for the inner is taken away and we've put that half on the spring seat itself."

While initial cost for the steel retainer is a higher, the overall cost is lower because it's not necessary to buy a new set of springs each time the engine comes in for its rebuild.

valve-springs PAC-spring-with-retainers

The sole drawback to the spring currently used by Shaver Specialties is the need for better lifters, and for that Shaver specifies 905 mm Jesel lifters.

"The stuff we were using five or ten years ago won't stay in - the bottom of the lifter is where the roller bearing swells - and then the clearance would stop," Hardesty says.

Shaver hasn't changed its spec on springs for more than 18 months.

Because engine builders compare notes on what they've tried or seen in their travels, Shaver Specialties learnt about this particular spring from one of its competitors. "While we were all whining about spring life, they said they'd tried this spring on one motor and that it worked pretty good," Hardesty says. "It's actually a drag racing spring made for severe duty over a short period of time, and while we were hesitant to try it, we did so out of desperation and it's a really, really nice valve spring."

Fig. 1 - Valve spring with intake and exhaust valves, seats and steel retainers.
Fig. 2 - Valve spring with steel retainers
(Photos: Anne Proffit)

Written by Anne Proffit

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