1. Basic Engine Terms

2. Dead Center –The term identifies the relation between the positions of the crankshaft and the piston. When the piston is at its outward most position from the crankshaft, and when the centerline axes of piston, connecting rod, and crankshaft are exactly parallel, the piston is said to be at Top Dead Center (TDC)

3. Top Dead Center Piston is at the top of its stroke. The crankshaft has rotated as far to the top as possible before it starts its downward rotation.

4. Bottom Dead Center When the piston hits the bottom of its descent in the cylinder.

5. Why is this important? Valve and ignition timing. –You want the piston to be moving up with both valves closed when the sparkplug ignites. –You want the intake valve to open when the piston starts its descent in the cylinder. –Everything needs to be in time in order for this to work.

6. Valve Timing

7. Piston Displacement Piston Displacement identifies the volume of air which a piston moves (displaces) in one complete stroke. It is used to describe the size of an engine in cubic inches (in3), cubic centimeters (cc), or in liters (L)

8. Piston Displacement Bore –Identifies the measurement of the cylinder diameter in inches or millimeters. Stroke –Determined by the number of inches or millimeters the piston moves from BDC (Bottom Dead Center) to TDC (Top Dead Center)

9. Calculating Piston Displacement V=A x h –V is volume of a cylinder in cubic inches or cubic centimeters –A is the area of a cylinder in square inches or square centimeters –h is the stroke of the piston in inches or millimeters

10. Calculating Piston Displacement

11. Example of Piston Displacement Bore = 2.750 inches Stroke = 2.25 inches

12. Compression Ratio Compression Ratio (CR) is defined as the total volume (TV) of the cylinder when the piston is at BDC to the cylinder volume when the piston is at TDC –TDC is called Clearance Volume (ClV) The difference is generally expressed as the ratio of the total cylinder volume to the clearance volume

13. Compression Ratio

14. Compression Volume Diesel Engines will usually have a much higher Compression Ratio. (19:1) Most Gasoline Engines will have a lower compression ratio (6:1 or 10:1)

15. Calculating Compression Ratio The total volume is obtained by adding the piston displacement volume and the clearance volume

16. Calculating Compression Ratio Piston Displacement = 13.36 Clearance Volume = 2.67