The chief engineer the M/V Katerina, which was equipped with pipes to bypass an important water pollution-control device, was sentenced today to eight months in federal jail for his conviction on obstruction of justice charges. Edgardo A. Guinto, 49, of the Philippines, was sentenced this afternoon in Los Angeles by United States District Judge Florence-Marie Cooper. Guinto pleaded guilty to the obstruction charge in January, admitting that he allowed the bypassing of the oil-water separator on the Katerina, that he instructed crew members to remove and conceal the bypass pipe when the ship came into Long Beach, and that he made fraudulent entries in the ship's pollution-prevention records known as the Oil Record Book.