In a deal that will strengthen its Salt Lake City-based savings and loan unit, Winn Enterprises of Fullerton completed the previously announced sale of a portion of the S&L;'s mortgage loan servicing portfolio for $5.2 million in cash. Sam Christensen, vice president of corporate development and treasurer for the diversified food, financial and real estate company, said the sale will result in $3.3 million in net income for Winn and will boost the net worth of its S&L;, MountainWest Savings and Loan, by 17%. Under the terms of the agreement, MountainWest will sell $230 million, or more than half, of the mortgage loans its services to Valley Mortgage, also of Salt Lake City. MountainWest, with $350 million in assets and nine branches in Utah and Wyoming, "is in fine shape" and profitable, Christensen said. Winn purchased the S&L; for $6 million in June, 1983, one month after it acquired the $500-million Knudsen Corp., California's largest dairy products firm.