Casey Stoner finished the first day of 2010 MotoGP testing in second position on the timesheets at Sepang in Malaysia.

The 2007 world champion took his new 'big bang' powered Ducati to a best lap time of 2min 1.902sec, which placed the Australian 0.491sec behind Yamaha's reigning world champion Valentino Rossi.

However the day was not as straightforward as it may have seemed, with attempts to solve a chatter problem hampered by roasting temperatures.

"Today was difficult to understand," confessed Casey. "We started off with a setting that was quite good, did a reasonably good lap time [on lap 12 of 42] and then tried a lot of different combinations to try and get the bike feeling a little better.

"We were having a few problems with chatter. We didn't really get any improvement, but the track conditions were so hot that it was difficult to understand if we were actually making progress.

"We were basically doing the same lap time even with a setting that felt good. We did a lot of 2min 1.9sec and couldn't really improve on that.

"Hopefully it will be a bit cooler [on Friday] so we can get some better track time, because we didn't understand a heck of a lot today."

Stoner is now planning some big changes for the second and final day.

"We've got a few big things to try tomorrow," he revealed. "We were trying a lot of small things for the first part of today, that didn't really help us, so we tried some bigger changes. We seemed to go in a circle but maybe that was to do with the temperature.

"We tried one new swingarm and we'll try another one on Friday. Hopefully we'll find an improvement, but the standard one we've had all along has been working very well. Both the carbon and aluminium standard ones.

"We're around 3-4 tenths away from where we want to be consistently."

Team-mate Nicky Hayden was seventh fastest out of the 17 riders, 1.381sec behind Rossi.