Reigning MotoGP champion Jorge Lorenzo insists he is on course to finish the season without an engine penalty, despite opening the fourth of his five engines after just six of 18 rounds.

Lorenzo and Factory Yamaha team-mate Valentino Rossi have each had one of their engines placed in 'observation'.

Yamaha engineers may yet be able to correct the unspecified issue, without breaking the seals, and thus return the engines to active duty.

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But even if not, Lorenzo is confident he can last the season by spreading the additional mileage across the other four engines.

"One engine is in observation, because we found some problems," confirmed Lorenzo, who has closed to within seven points of Honda's world championship leader Dani Pedrosa after wins at the last two rounds.

"So maybe it is possible to use that engine again in the future. But in theory - and as Ramon [Forcada, crew chief] says - even if it is not possible to use it again, we will finish the championship [without needing an extra engine] anyway.

"In theory there is no problem, as long as we don't break another engine."

Lorenzo faced a similar situation last season, when he was taken down in a first-turn accident at Assen that also broke a newly-introduced engine. The Spaniard suspected he may have to limit his practice mileage thereafter, but finished the season without issue and claimed his second premier-class title.

MotoGP has toughened its engine durability rules further this year, down from six to five engine changes per rider. The penalty for each additional engine is a pit lane start, 10 seconds after the green light is displayed.

Repsol Honda riders Pedrosa and Marc Marquez are said to still be on their second engine of the year.

Meanwhile, on the chassis front, both Lorenzo and Rossi are now using the same frame specification. Two versions of the M1 frame have been available since winter testing and, while Rossi always preferred the 'standard' design, Lorenzo spent several events trying out the newer version.

"Now Jorge uses the same frame as me," said Rossi. "The two chassis are very, very similar. Small differences. But now I think we have the same spec."

Monster Yamaha Tech 3's Cal Crutchlow also felt the new chassis was a step back after running the frame in Monday's Catalunya test.

"I tested a new chassis that Jorge used at the first couple of races and it isn't any better than the frame I am on," said the Englishman. "I did the whole day on the new frame and braking stability was better but in other areas it didn't feel quite as good.

"At the end I went out again on my old chassis and was immediately as fast as before and I was using a set of tyres that had already done 25-laps... I will continue to use that frame."

Don't miss out! The next round of the 2013 MotoGP World Championship takes place at Assen on June 27-29 - CLICK HERE to see ticket prices from the Official MotoGP Ticket Store.