Bamber is teamed with Formula One driver Nico Hulkenberg (Germany) and Nick Tandy (Great Britain).
Hartley, with Mark Webber (Australia) and Timo Bernhard (Germany), had started from pole position in Belgium last month but dropped back due to a penalty and a technical failure. They fought their way back to finish third.
Changing weather conditions in the west of France provided the team with challenges regarding set-up work, but also with the opportunity to test on a dry, a damp and a fully wet track.
"Certainly the test programme was somewhat limited because of the changing weather conditions," Porsche team principal Andreas Seidl said.
"For reliable tyre evaluation I'm sure all the teams would have wished for a consistently dry track ...
"It was important that all three Porsche 919 Hybrids were running all day. Our new drivers completed their mandatory 10 laps to be allowed into the race.
"As far as you can judge from the lap times, we will see very tight competition among the front runners," Seidl said.
Bamber appeared comfortable in the new surroundings.
"It was incredible to drive the Porsche 919 Hybrid for the first time in Le Mans. It is a beautiful track - one of the best in the world," Bamber said.
"The speed of the car is incredible and the hybrid system is amazing. With the four-wheel drive system it is a pleasure to drive in the rain - it is like driving in the dry.
"It was magical to take the Porsche curves for the first time with around 230km/h. We completed a good mileage and are up to speed."