The overall ratings of three machinery stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Navistar International Corporation’s (NAV) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. Navistar International manufactures and markets medium and heavy trucks, school buses, mid-range diesel engines, and service parts. In Portfolio Grader’s specific subcategories of Earnings Revisions, Cash Flow and Sales Growth, NAV also gets an F. As of Jan. 3, 2014, 13.3% of outstanding Navistar International Corporation shares were held short. For more information, get Portfolio Grader’s complete analysis of NAV stock.

Kaydon Corporation’s (KDN) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). Kaydon designs, manufactures, and sells custom-engineered products for a variety of industries, including aerospace, defense, and industrial. The stock receives F’s in Earnings Growth, Earnings Momentum, Cash Flow and Margin Growth. The stock currently has a trailing PE Ratio of 37.20. To get an in-depth look at KDN, get Portfolio Grader’s complete analysis of KDN stock.

Donaldson Company, Inc. (DCI) earns a D this week, moving down from last week’s grade of C. Donaldson is a worldwide manufacturer of filtration systems and replacement parts. The stock has a trailing PE Ratio of 25.60. For a full analysis of DCI stock, visit Portfolio Grader.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.