BTR LS valve stem seals are designed for stock powdered metal and bronze guides; some include a built-in locator for single springs, and some use separate locators. The valve stem seals allow a carefully defined amount of engine oil from the cylinder head into the combustion chamber—to lubricate the rotating valve stem in the valve guide. BTR valve stem seals are produced from high performance materials for increased part life and lower wear. Order the set recommended for your year/make and engine application.