MOUNT DIABLO -- A retired industrial manager, an optics expert, an electrical manager, a developer, a veterinarian with a knack for restoring clocks -- it took a village to return the spark to the top of Mount Diablo.

Built in 1928, a rotating beam on the mountain's peak has for the last 50 years been a treasured memorial to Pearl Harbor victims. But age -- it was built in 1928 -- extreme mountain weather conditions and lack of state park maintenance funds had made the "Eye of Mount Diablo" a possible no-show for its annual Dec. 7 performance this year.

Then a band of highly-skilled retirees stepped forward to guide a $100,000 volunteer restoration, overseen by a conservation group.

After four months of work on everything from bulbs and bolts to glass and gears, the team of Save Mount Diablo volunteers has completed the overhaul, and the beacon will shine again.

"We like to work with our hands," said Dick Heron of Danville, a retired Del Monte food production manager who has helped oversee the restoration in a donated Concord warehouse space. "The beacon is a mechanically simple device. The big challenge is making improvements while maintaining the historical integrity of the beacon."

The beacon -- a lamp focused into a stream of light by a mirror -- operated as a homing device for planes and ships from 1928 until it was extinguished after the Japanese attack on Pearl Harbor on Dec. 7, 1941. In 1964, the state park system and veterans reactivated the "Eye of Mount Diablo" to sweep the skies one night a year -- on Pearl Harbor Day.

Even deciding what color to paint the metal casing and housing for the beacon took weeks to decide.

Analysts detected seven different paint colors that had been applied to the metal over 85 years, including a drab olive green that remained a strong candidate until a week before painting was to begin.

But a state park historical expert tracked down a 1941 photograph that showed the beacon housing was silver back then. "The historian found the proof, so silver it is," Heron said.

The project's state historical monitor nixed an idea to recoat the beacon mirror because it was original and considered vulnerable.

Some beacon parts, however, were broken and had to be replaced -- with a little help from friends from all over the Bay Area.

After restoration workers discovered broken bearings in the mechanism that turns the beacon, Shell oil refinery workers in Martinez supplied one duplicate off their shelves, and ordered another from a supplier.

But finding replacement parts wasn't always simple.

Fortunately, one volunteer, Allan Frank, had experience at a Lawrence Livermore Lab optical lab so he could determine what type of glass was needed for the slats in the round protective covering for the beacon.

Dick Heron connects a brass flange, fitted with"strain reliefs" where the top of the main shaft connects with the yoke of the beacon during
Dick Heron connects a brass flange, fitted with"strain reliefs" where the top of the main shaft connects with the yoke of the beacon during rehabilitation of the beacon at a warehouse in Concord, Calif., on Saturday, Sept. 14, 2013. (Susan Tripp Pollard/Bay Area News Group)

And operators of an Alameda manufacturing plant donated use of their industrial water jet to cut the glass slats to fit.

On a Monday morning last month in the Concord warehouse, volunteer Burt Bogardus, a retired park ranger, checked gears and equipment spread out on the floor.

Nearby, John Stuart, a former PG&E electrical expert, prepared to turn on the beacon for the first time since it was taken apart.

"We expect it to work," he said. And it did, casting a bright light on the warehouse wall. Stuart gave little reaction until after he walked to the wall and measured the light intensity. "Yes," he said, "It's what we expected."

Then he smiled.

The beacon will be trucked back to the summit later this month.

Julie Seelen, Save Mount Diablo's advancement director, said the restoration would have been impractical without the donated labor and services -- including the use of a crane to remove and then reinstall the beacon.

The restoration won an honor last month. The East Bay Leadership Council, a business-oriented public policy group, gave the project its 2013 philanthropy award for an outstanding collaborative project.

Heron said respect for Pearl Harbor survivors motivated their band of volunteers to spend long hours on the restoration.

"What makes the beacon special is the veterans," he said, "and keeping the connection between the light and their service."

Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff.