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The mammoth Highway 99 tunnel machine will start its journey under Seattle a few weeks late, after workers at the Japanese assembly site found damage to the rotary drive that spins the cutter head.

Instead of a June 3 launch, the boring machine will embark from Sodo to South Lake Union sometime this summer, said Chris Dixon, project manager for Seattle Tunnel Partners.

“It doesn’t affect the overall schedule, as far as completion and turning it over to traffic in December 2015,” Dixon said Wednesday.

Testing was to be finished Dec. 25. As of this week, Hitachi-Zosen crews in Osaka are disassembling and diagnosing the drive system.

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The world-record 57½-foot-diameter drill must be reassembled and retested before shipment to Terminal 46 in Seattle.

Workers had heard sounds indicating a problem, which went away, before a completion ceremony Dec. 20, said Dixon.

Shortly after, the team discovered some parts were one-fifth of an inch out of alignment, he said.

Linea Laird, project administrator for the state Department of Transportation, notified a legislative committee of the problem Wednesday.

Dixon said he was glad to find the flaw now, instead of in the ground.

The team has at least a three-month cushion, and many chances to recover lost time, Dixon said.

This is because an innovative design allows workers to replace worn-out cutting tools from inside the 300-foot cylindrical machine — reducing the need for divers to work from outside at several times atmospheric pressure.

The $2 billion tunnel is the largest piece of a $3.1 billion replacement for the Alaskan Way Viaduct, built in the 1950s.

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

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