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Seattle Tunnel Partners will try to restart the stranded Highway 99 tunnel machine by Sept. 1, the team’s project director, Chris Dixon, announced Friday.

Dixon also acknowledged for the first time that the main bearing shows symptoms of damage. The circular, 35-foot diameter part must be in prime condition for drilling to occur — because the bearing contains rolling parts that allow the machine’s two dozen electric motors to turn the round cutter head.

Over the next few months, a 120-foot-deep pit must be dug in front of the machine so that workers can remove or bypass the cutter head and reach the bearing. Dixon said Friday that all seven of the bearing’s rubberized seals, which block grit from reaching the bearing rollers, must be replaced.

A spare bearing is now stored in Osaka, Japan, he said, and will be shipped to Seattle — so that the job doesn’t lose any time if the full bearing replacement is needed.

A full repair plan by Hitachi-Zosen, which built the machine, is due in 10 to 14 days, Dixon told reporters at a news conference on Pier 48. A few yards away, the drill known as Bertha is stuck underground near South Main Street.

A Sept. 1 restart would amount to a nine-month stoppage overall.

Dixon himself called the date slightly optimistic. “What we try to do in construction is set a goal and get everybody focused on that,” he said.

Construction of the pit, lined by concrete walls, could start in a few weeks. After it’s done, Bertha would drive forward several feet and churn through the south wall into the work zone. But cranes and other equipment wouldn’t be set up until April because contractors on Seattle’s seawall project now occupy the land north of Bertha.

The world’s widest tunnel-boring machine halted Dec. 7 when it overheated, and sand was found in the bearing grease. Bertha has advanced only four feet since.

Representatives of the bearing manufacturer, Rothe Erde of Germany, have inspected the machine’s front end. Asked in an interview if sand or saltwater made it all the way into the rolling parts inside the bearing, Dixon said: “There’s a suspicion they might have, but they don’t know that now.”

That’s a change from earlier statements by both Dixon and Washington State Department of Transportation (WSDOT) officials, who said for weeks that the main bearing seemed intact. Hitachi-Zosen is still working on its “root cause” analysis of why the seals failed, officials say.

Such knowledge is crucial, to reduce the odds that Bertha might stall again — but this time downtown at depths of up to 200 feet. It would be difficult if not impossible to dig a front-end repair shaft alongside Pike Place Market, for instance.

In that scenario, workers would do repairs from the back end, Dixon said. To give the workers access, it would be a lengthy maneuver that entails moving the trailing gear, conveyors and the heavy robotic arms that lift and set concrete tunnel segments.

An expert review panel report this week said the tunnel highway project will slide a few months past the Dec. 31, 2015, completion date to open for traffic, and instead likely be done by mid-2016.

Dixon said Seattle Tunnel Partners hasn’t revised its own schedule yet. Project supporters believe time can be regained by working 24/7, and by starting now to build the double-deck highway.

Meanwhile, the Alaskan Way Viaduct will be closed from 6 a.m. to 6 p.m. Saturday and Sunday for routine maintenance and repairs.

Mike Lindblom: 206-515-5631 or On Twitter @mikelindblom