Chevrolet has confirmed that it was a batch of valve springs that led to the engine problems they experienced in St Petersburg.
Jim Campbell, Chevrolet's US vice president of performance vehicles and motorsports, revealed that it was the valve springs that led to the to 11 of the 12 Chevrolet engines needing 'non-minor' repairs following the first round.
“We identified a batch of valve springs that, due to a process change at one of our suppliers, may fracture before the full mileage requirement (2500 miles)," said Campbell.
"We notified IndyCar of the issue and obtained approval to change the valve springs.”
The points penalty is because the engines did not go the full 2500 miles without a major repair
IndyCar on penalties issued to Chevrolet
The change was made to 11 of Chevrolet’s 12 IndyCar engines, as the final engine had “lower accrued mileage."
"The current plan is to address the 12th engine after the race at Barber Motorsports Park,” added Campbell.
IndyCar had already confirmed that “the non-minor (major) repair that Chevrolet performed on 11 of its engines was completely legal and above-board with respect to the rules,” according to Marvin Riley, IndyCar director of engine development.
“We were notified of the change and an IndyCar representative was present for the entire repair process, even resealing the engines before departing their facilities (Ilmor Inc. in Plymouth, Michigan).
"The points penalty is because the engines did not go the full 2500 miles without a major repair.
“Chevrolet replaced like-for-like parts in their engine when making their repairs, so no new or unapproved parts were installed. The repair involved only replacing used with fresh parts."
Not a unique problem
Valve springs can be manufactured using heat processes and could be susceptible to breakage in extreme conditions experienced in the Verizon IndyCar Series. Tool steel materials used in the triple-spring common in this type of racing can vary from batch-to-batch and it would seem that is the issue here. A brittleness can occur when the material is not sufficiently durable for this type of endurance work.
While this isn’t a common problem for IndyCars, getting valve springs to live for long distances in drag racing, particularly in Pro Stock competition, is often quite difficult.
The amount of lift and cam work done on an engine is critical to valve spring life, in particular for the elongated distance of 2500 miles as decreed by IndyCar. In NASCAR, for instance, valve springs are typically changed out for every race but with seals on the engines, that’s not possible to do on an IndyCar.
By finding this defect prior to it hurting the rest of the engine, Chevrolet might have paid a smaller price than it would have with catastrophic engine failure due to valve spring issues.