Walkinshaw TWG Racing reveals cause of Chaz Mostert DNF
Bottom-end bearing issue behind Mostert's Ipswich retirement
All five Toyota Supercars to revert to 'A-spec' engines for test day
Toyota homologation squad Walkinshaw TWG Racing has revealed that a bottom-end bearing issue was behind Chaz Mostert's DNF in the Ipswich finale.
The reigning champion was ruled out of Sunday's race while running sixth, marking Mostert's second engine-related DNF of the season. Mostert was one of two high-profile engine-related retirements, alongside erstwhile Sprint Cup leader, Ford's Matt Payne.
Walkinshaw TWG Racing and Supercars quickly stripped down the engine on Monday and completed a forensic analysis of the failure, which has since been diagnosed.
In a team statement, Walkinshaw TWG confirmed all five Supras — its cars for Mostert and Ryan Wood, and the three Brad Jones Racing entries — will revert to the 'A-spec' engine for Tuesdays' enduro test, also at Queensland Raceway.
The team also confirmed that all five Toyotas will have the upgraded B-spec engine fitted for The Bend.
The statement reads: "Following a complete analysis of Car 1’s engine following Race 28 of the 2026 Supercars Championship, Walkinshaw TWG Racing can confirm a bottom-end bearing issue was the root cause of Car 1 failing to finish the race.
"The Team, alongside Supercars, is already putting measures in place to address the origin of the issue, to avoid any reoccurrence.
"All five GR Supras will run the A-Spec engine at tomorrow’s Supercars test day at Queensland Raceway, while all B-Spec engines will be inspected as a precaution, before returning to cars for The Bend 500, as planned."
In the statement, CEO Bruce Stewart thanked his crew and Supercars staff for the quick analysis, saying: “While these things shouldn’t happen, within 16-hours of the race yesterday we had the engine stripped, root cause identified and way forward implemented which is a credit to our staff, and to Supercars as well who have worked alongside us on it. It was a real positive element of a challenging situation.
“Returning to the A-spec engines for tomorrow is a precaution, as we inspect all B-Spec engines, but it’s important to note that this was not valve-train related, the area that was updated for this event.
“All GR Supras on the grid at The Bend 500 will have a B-Spec engine fitted, as planned.
“We will continue to work around the clock to increase the reliability and engine strength as we head into the endurance season. The work hasn’t, and won’t stop.”
The 2026 season hits enduro mode at Tailem Bend on September 11-13.
