Four-cylinder engines 1976 and later all drive the camshaft(s) and intermediate shaft with a toothed timing belt. This part is replaced during normal maintenance every 45,000 or 50,000 miles, depending on your year and model. It is highly advisable to change the seals on cam, intermediate and crank shafts when changing the belt at 90,000 miles or more. Additionally, at 135,000 or more miles, consider replacing the timing belt tensioner, since its bearing will not last much longer. Always carefully inspect the crankshaft sprocket for cracks along the keyway that locks it to the crank. If your front seals (or any engine seals) are leaking, or you find your dipstick pushed up after running the engine, check your flame trap! (See related Tech Tip)