Toyota's Drive Train

Toyota's Drive Train

Component Tolerance



One of the main reasons for the legendary reputation of Toyota engines is the maintenance of exacting tolerances on internal components, which are measured right down to the micron... one thousandth of a millimeter.



To illustrate how minute a micron really is, circle A represents the diameter of a strand of human hair, magnified several thousand times. To the same scale, circle B is one thousandth of an inch, a common unit of measurement in the automobile industry. Circle C is a ten-thousandth of an inch, used less frequently for more precise measurements. Finally, the small dot represents a micron... Toyota's standard unit of measurement... one fiftieth the diameter of human hair... the unit used by scientists for determining distances like the wavelength of infrared light.



To maintain these exacting tolerances in engine production facilities, randomly selected components from the production line are frequently checked using precision test instruments.



This engine block is being tested to ensure all parts have been machined properly in relation to one another... so the entire motor fits together perfectly.



Surface roughness or microscopic scratches on contact surfaces can cause friction and additional wear. A camshaft lobe may look smooth to the naked eye, but magnify it 5000 times, and any defect becomes visible.

Engine Assembly



After the engine block has been machined, each and every one is measured... right to the micron. This precise measurement is stamped right on the component, so that later, during the assembly process, the block can be mated with perfectly matched components.



To maintain optimum spacing for oil lubrication between the crankshaft and the cylinder block journal that cradles it, one of five bearings is selected... with each bearing only a three-micron difference in thickness from the next. A strand of hair between bearing and crankshaft can damage the engine.



Based on the exact dimension of each cylinder, one of three different sizes of piston is selected. Once again, the variation in size between them is minimal... only a few microns.



Many components have temporary plastic covers, to prevent metal surfaces from being scratched during assembly.

Engine Testing



Rigorous testing is one reason why the reliability of Toyota engines is so consistent, and so legendary. Every single one is fired up and run for 15 minutes on a giant turntable. Once operating temperature is reached, over a hundred items are checked.



On a daily basis, engines are pulled randomly from the line, and put through an extensive three hour performance test. Then, they are completely torn down, and each part evaluated.



Once a month comes some of the most torturous testing of all... where the engine revs from idle, up to 6300 RPM, and back down to idle, in seven seconds... 200,000 times! The entire process goes on for four weeks.



The monthly durability test is equally as demanding... 180 hours of continuous operation... full throttle all the way. The engine works so hard the exhaust manifold glows in the dark.