The mechanic blamed for a 2008 tower-crane collapse that killed two men on East 91st Street will not go to jail, providing he cooperates against his millionaire boss, James Frank Lomma, at a manslaughter trial now set for December, it was revealed yesterday.

In taking a reduced plea, from manslaughter down to criminally negligent homicide earlier this month, the mechanic, Tibor Varganyi, fingered Lomma for saving money by repairing a metal bearing on the cheap by having it rewelded in China.

“Lomma never asked you what you were providing to [the Chinese welders] for use in the design of the bearing, nor did Lomma obtain assistance or oversight of a professional engineer or any other person competent to design as complex a piece of equipment as a bearing?” prosecutor Deborah Hickey asked Varganyi.

“It’s true,” he replied.