CAPE CANAVERAL, Florida - A spacewalking astronaut ran into trouble Sunday while trying to lubricate a joint in the life-sustaining solar power system of the International Space Station, losing one bolt and getting a washer stuck in a crevice.

Mike Fincke, one of NASA's most experienced spacemen, had to settle for a partial lube job, after the bolts holding down covers on the massive joint started popping off unexpectedly.

"Bummer," said his spacewalking partner, Andrew Feustel.

The spacewalk _ the second of four planned for shuttle Endeavour's final space station visit _ went 1{ hours longer than planned as Fincke and Feustel did what they could with the joint. They managed to lubricate four sections, two fewer than planned, and reinstall three covers. The fourth cover was brought back inside because of the missing bolt and washer.

"You guys earned your pay for the day," astronaut Gregory Chamitoff radioed from inside as the spacewalk hit the 7{-hour mark. The spacewalkers joked about getting paid, saying their reward was being outside watching the world spin by.

The eight-hour, seven-minute spacewalk, the sixth-longest in history, started out well as Fincke and Feustel quickly topped off a leaky radiator line.

Ammonia is extremely hazardous, and the two did their best to avoid contaminating their spacesuits while replenishing the system with 5 pounds (2.25 kilograms) of the substance. Some frozen ammonia flakes floated toward Feustel as well as a small icy chunk, but he didn't think any of it got him.

Fincke moved on to preventive maintenance on the joint that rotates the solar wings on the left side of the space station. He was removing his first cover when a bolt popped out and got away from him. He caught it. But another bolt ended up floating away, and a washer got stuck between the cover and an attachment.

Mission Control worried the washer might get into the gears of the joint. Fincke was advised to use "gentle backhand sweeping motions" to get the washer away from the gears, and the astronaut said he could try to coax it out.

All this came as a surprise, and Mission Control later told the astronauts the washers might be bent and flimsy from previous repair efforts.

"Sorry you're having such a hard time with those bolts, buddy," Feustel called out to Fincke.

"Yeah, man, I was being really careful, too," Fincke replied.

After deliberating, flight controllers instructed Fincke to remove four covers from the joint rather than six, to lubricate the mechanisms inside.

Another bolt popped out and almost got away, but Fincke caught it. "He gets the golden glove award for another catch," Mission Control radioed.

To Fincke's relief, the remaining covers came off much more easily.

Fincke and Feustel used grease guns to squirt the dark lubricant onto the gears, then turned to other tasks as the joint was rotated to spread the grease. They returned for more lubricating once the motion stopped, after assuring Mission Control that they had the energy to continue.

NASA wants to lubricate as much of the joint as possible to keep it functioning properly in the years ahead without shuttle visits.

The circular joints _ 10 feet (three meters) in diameter _ turn the space station's solar wings toward the sun, like the paddle wheels of a boat. Each set of wings measures 240 feet (73 meters) from tip to tip. The panels collect sunlight and convert it into electrical power that's used to run equipment aboard the outpost, including the life support.

This is the next-to-last shuttle mission and the final spacewalks of the program scheduled, meant to leave the space station in the best condition possible for the next decade. The 30-year shuttle era will end in July with the flight of Atlantis.

This was Fincke's seventh spacewalk and Feustel's fifth. They praised one another as they headed out the hatch.

"It's an honor to be walking, spacewalking with a Hubble spacewalker," Fincke told Feustel, part of the 2009 Hubble repair team.

"It's an honor to be walking with the man with the most time in space," Feustel replied. Fincke will become the most traveled American in space by next weekend, surpassing the current record of 377 days aloft.

On Monday, three of the six space station residents will head home in their Russian Soyuz capsule after a five-month mission. In a unique photo op, the departing crew will photograph Endeavour parked at the space station.

Then on Wednesday, Fincke and Feustel will venture back out for spacewalk No. 3.

Endeavour, under the command of Mark Kelly, husband of wounded Rep. Gabrielle Giffords, will remain at the orbiting outpost for another week. Landing is scheduled for June 1.