Yuki Tsunoda and Lance Stroll are both set to start their Mexico City Grand Prix from the back of the grid on Sunday following engine changes undertaken in the AlphaTauri and Aston Martin teams.
Both Honda and Mercedes have allocated a fourth internal combustion engine, turbocharger and MGU-H and exhaust system to their respective drivers.
Furthermore, Honda has also handed a seventh exhaust element to Sergio Perez, but the change is penalty-free as the Mexican remains within the authorized limit.
Stroll's engine change follows a worrying trend in the Mercedes camp, with reliability concerns forcing the German manufacturer to preemptively introduce new elements into the pool of hardware of several of its drivers.
In Austin, Valtteri Bottas was assigned a sixth ICE, while Sebastian Vettel was also assigned a new unit.
It's unclear if championship contender Lewis Hamilton will be able to conclude his 2021 season without an engine change and a subsequent grid penalty, but the odds appear low.
Hamilton has said that he doesn't expect to take on a new PU, but in the opposing camp, Red Bull motorsport boss Helmut Marko is convinced Mercedes will need to assign fresh hardware to its star driver.
“If the races go normally and there are no accidents, we will get through with our engines,” said Marko during an interview with Auto Motor und Sport.
“So far, we have been absolutely reliable with the Honda engine.
“You are never immune to a defect. But the engine situation is certainly more reassuring on the Honda side than on the Mercedes side.
“Our information, our hope, is that Hamilton will have to change again.”
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