Yamaha may have mathematically won the 2009 MotoGP Constructors' Championship, with three rounds still to go, but the factory can't celebrate just yet.

With Valentino Rossi or Jorge Lorenzo winning all but four of the 14 rounds so far, Yamaha has built a lead of 94 points over nearest rival Honda - with a maximum of 75 on-track points still to be won.

However, the new limit on engine changes - specifically the penalty for exceeding the five changes allowed during the final seven rounds - means Yamaha, like all manufacturers, could potential have points deducted before the end of the season.

Initially it was to be the rider that suffered a 10 point penalty for each extra engine change, but a modification of the rule at Estoril declared that the rider will instead start from the back of the grid while 'the constructor will have 10 points deducted from its championship classification'.

As such, Yamaha must wait until the end of the season to celebrate.

However, the factory is now guaranteed of winning the Riders' title with either Rossi or Lorenzo, while Fiat Yamaha has wrapped up the Teams' championship with an unbeatable 167 point lead over Repsol Honda.

"We have achieved the first objective of our season - the Fiat Yamaha Team becoming 2009 Teams' Champion," said team director Masahiko Nakajima. "I would like to thank our riders, our team staff and YMC MotoGP Group Engineers for their invaluable support, which has allowed us to achieve this great result."

Rossi and Lorenzo have given Fiat Yamaha a maximum 45 point (one-two finish) haul at five races this season.

"As a consequence of the entire season, which has been dominated by the two Fiat Yamaha Team riders, we have won the Team title," said Rossi's team manager Davide Brivio.