Andrew Benson
Chief F1 writer

Image source, Getty Images

More trouble for McLaren-Honda has arrived in the shape of a loss of power and subsequent engine change. Honda has fundamentally revised the architecture of the engine this year and although F1 boss Yusuke Hasegawa has not fully confirmed the layout, sources have told BBC Sport that they have copied Mercedes’ split-turbine philosophy. 

This puts the two parts of the turbocharger - the compressor and turbine - at opposite ends of the engine vee, joined by a shaft on which sits the MGU-H, the unit that recovers energy from that part of the engine. The main engineering difficultly of this is controlling reliability on such a long shaft spinning at up to 125,000rpm. 

It was already known last summer that Honda were planning this and I spoke to Hasegawa about it then. 

“Splitting turbine is not to make the turbine bigger,” he said. “It makes the centre of gravity lower, mainly. That is the only advantage. But it is a very big advantage. The MGU-H is more than 25kg and it is very high up. So it will give us huge benefit, even if the turbine is the same size.” 

He admitted his concerns then about the turbine shaft. “Very difficult,” he said. “The turbine is rotating more than 100,000rpm. The limit is 125,000. It has huge mass for the turbine and compressor. It is very hard to realise. That’s why Ferrari and Renault doesn’t create that. So that’s why I can’t tell if we can realise that.”

We don’t know if that is the problem with the Honda engine, but it gives a sense of the scale of the challenge facing them.

A late blast on the supersoft Pirelli tyre sees Hamilton and Mercedes set the fastest time of the week so far. 

A 1:20.983 is eight tenths up on his previous best time, which was set on the soft tyre. 

He's two seconds up on secodn-placed man Kimi Raikkonen, although the Ferrari man has only lapped on the medium tyre. 

With all these variables in play, it's hard to know whether to get excited by Hamilton's time or not...  

A new personal quickest lap for Verstappen in fourth. He does a 1:23.212.

Hamilton still leads, followed by Raikkonen and Ocon. 

Thirty minutes to go. 

A 2001 Arrows there. Definitely not the new McLaren. No siree.

Those well-connected chaps over at Autosport are reporting that Renault hope to get a run in before lunch. They add that today's absence of track action is down to fitting new parts that arrived overnight.  

This run should get the three-time champion past the race-distance mark today, having put on 73 laps yesterday.

As we thought, Hamilton pits after bringing up his 50th lap - 51 to be precise.

More useful mileage for the Briton and the team, who are yet to report any reliability issues.

It was a slow start to the day for Force India - a legacy of exhaust problems yesterday - but they are flying now.   

On the soft tyre, Esteban Ocon has just done a  1:23.180 to displace the Red Bull of Max Verstappen in third place.  

Kevin Magnussen is the only driver making improvements at the moment. His latest lap is a 1:24.935. He stays fifth, half a second of Ocon's Force India. 

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Hamilton is blatting around with metronomic precision again. Having gone round just 0.001s slower than his best time yesterday a little earlier, he then does a time 0.006s off that pace.

He's done 37 laps and it would seem he's now on a 15-lap stint on the soft tyre, which would take him up to the 50-lap mark.

Just nine laps completed for Esteban Ocon today, albeit good enough for fourth place.