By Alan Baldwin
SILVERSTONE, England (Reuters) - Triple world champion Lewis Hamilton's chances of pole position at his home British Grand Prix were boosted on Friday after a gearbox change left Mercedes team mate Valtteri Bottas out of contention for the top slot.
The Finn, on pole twice this season and fastest in both practice sessions at an overcast Silverstone, will collect an automatic five-place grid penalty after Saturday's qualifying.
Hamilton, who is 20 points behind Ferrari's Sebastian Vettel after nine races but chasing his fourth successive home victory, had a similar problem at the previous round in Austria which Bottas won from pole.
"His gearbox was damaged in the same way as Lewis's but less severely, and we had hoped to coax it to the end of the cycle," said a Mercedes spokesman.
"However, we have not been able to do so. The cause of the damage is understood and now behind us, just as for Lewis's problem."
Bottas, who won the previous race in Austria, had earlier produced a best lap of one minute 28.496 seconds - significantly quicker than Hamilton's 2016 pole position time of 1:29.287.
Hamilton, who bounced over kerbs and grass in the afternoon, was 0.078 behind in the morning and 0.047 off Bottas's pace after lunch when the Briton was on slower tyres.
"The track is absolutely incredible with these new cars. It was already one of the very best circuits in the world, but with this car and the speed we are able to carry through the corners, it's just phenomenal," said Hamilton.
"It's like the greatest rollercoaster ride ever. We worked through all the sessions, fine-tuning the balance and I think we're in a good position at this early stage of the weekend."
Ferrari, more than a second slower than Bottas in the opening session, ended the afternoon as Mercedes' closest rivals with Kimi Raikkonen third and championship leader Sebastian Vettel fourth.
Red Bull's Dutch teenager Max Verstappen, who has had five retirements in the last seven races, was third and fourth respectively in the sessions while Australian Daniel Ricciardo was fourth and sixth.
"Mercedes look really strong but we look to be in the fight with Ferrari. At the moment we're battling Ferrari and not Mercedes," said Ricciardo, who has been on podium for five races in a row.
Vettel started the day by trying out the new "shield", the first driver to experience the transparent open canopy system designed to protect the head from flying debris.
The test was not an immediate success.
"I got a bit dizzy," said the German.
"Forward vision is not very good. It's probably because of the curvature, you get quite a bit of distortion, plus you get quite a bit of downwash down the straights pushing the helmet forwards.
"We had a run planned with it, but I didn't like it so we took it off."
Williams technical head Paddy Lowe said he thought it looked "pretty good" otherwise.
"We're worried about reflections but there may be solutions to that. We will be testing it on various cars over the coming months," he added.
(Reporting by Alan Baldwin; Editing by Ed Osmond)