(Adds analyst comment, background, updates shares)
Dec 20 (Reuters) - Navistar International Corp reported another quarterly loss on Friday as the vehicle maker continued to struggle to right itself after its introduction of an engine emission technology that failed to comply with tough environmental rules.
Shares in the U.S. truck, bus and engine manufacturer tumbled 5 percent in early trading Friday.
Ann Duignan, an analyst at JP Morgan Chase, called Navistar's latest results, which were pulled down by warranty costs and other outlays associated with its proprietary emissions system, "messy and below expectations."
The company has also been hurt by lower demand for trucks, especially from the U.S. military as the government cut spending.
Revenue dropped to $2.75 billion in the fourth quarter ended Oct. 31 from $3.18 billion a year earlier.
Net loss narrowed to $154 million, or $1.91 per share, from $2.77 billion, or $40.13 per share, a year earlier. Analysts, on average, expected a loss of $1.63 a share, according to Thomson Reuters I/B/E/S.
In early trading on the New York Stock Exchange, the company's shares were last down $1.77, or 4.5 percent, at $37.69. They have risen about 50 percent in the past six months, outperforming the 14 percent rise in the S&P 500 index. (Reporting by James B. Kelleher in Chicago and Sagarika Jaisinghani in Bangalore; Editing by Joyjeet Das and Nick Zieminski)