12-Cylinder Firing Order Display



NOTE: You must have the Java Runtime Environment (JRE) installed on your machine for this applet to function correctly.
Java is a free download. Recent version of the Java Runtime Environment on some Windows machines complain that this application is not digitally signed and is thereby a security threat. The AEHS has not put anything into the application that makes it a threat, and the warnings can be worked around by answering the appropriate questions.


1. Select an engine from the pull down menu at the center of the applet canvas.
2. View the characteristics of that particular firing order.


Most people look at tabulated V-12 firing orders with a degree of confusion and dismay. Not only does it first appear that the 12-cylinder sequence is random, the nomenclature often obstructs by introducing numbering schemes and letters such as A, B, L, R, D, G to describe the left and right banks. Also, manufacturers use different references as to the location of number one cylinder; it maybe either next to the propeller, or on the anti-propeller end. Additionally, the engine might be either upright or inverted! In an effort to make V-12 firing orders comparable, the author uses a naming convention adapted from the German V-12 manufacturers. Beginning at the propeller, cylinders 1-6 are in the right bank, and 7-12 on the left. This applies whether the engine is upright or inverted. With this convention it is also necessary to know the direction of rotation of the crankshaft, either CW or CCW as viewed from the rear, looking toward the propeller. This resolves the complexity of direct drive, or geared, and removes confusion caused by the characteristics of different types of gear systems, such as internal or external spur gears, or epicyclic. Note that engine data plates typically use a propitiatory manufacturer nomenclature, as well as describing only the direction of rotation of the propeller.

Description of the Display

At the left of the canvas is a diagram of the 12-cylinder firing sequence. The columns of numbers closest to the graphic (labeled "N") represent  the normalized cylinder numbering scheme. The other columns of numbers (labeled "DP") represent  the data plate cylinder numbering scheme.

In the center of the canvas is an isometric view of the crankshaft that depicts the bank firing sequence of the engine. The small arrow at the front of the crankshaft indicates the direction of CRANKSHAFT (not propeller) rotation. Note that in all cases the crankshaft has a 6-throw, 120° configuration with crankpins pairs 1-6, 2-5, and 3-4 in the same planes. The arrows depict the firing order of a single bank. Other considerations aside, it is desirable for bank firing sequences to alternate from one end of the block to the other. This improves breathing and scavenging behavior of the engine. The bank firing sequence graphic facilitates visualization of intake and exhaust flows.

At the right of the canvas is a diagram that allows visualization of crankpin loading order. This is an important factor in vibration reduction. A good example is the Junkers Jumo 213. The three examples (213, 213 with Rechlin order, and 213E) show how changes in firing order made a reliable engine out of one that was breaking crankshafts. The problem was too many torque reversals per cycle. This was cured in the 213E by choosing a firing order that systematically loaded and then unloaded the crankshaft.

This tool works for any 12-cylinder engine with cylinder pairs connected to the same crankpin of a 6-throw, 120° crankshaft, regardless of bank angle. Because of this, we have included several opposed and H-configuration engines. You can also enter a new firing order by filling in the table that appears if you click on the "Create Custom Firing Order" button. In order for the results to be meaningful, the firing order you enter must be one that can be achieved by a 6-throw, 120° crankshaft within 720° of crankshaft rotation.

Future Developments

It is our desire to expand the number of engines represented to include many more 12-cylinder engines, including automotive, traction and marine applications. Please send the data plate firing order, a description of the cylinder numbering scheme and direction of crankshaft rotation when viewed from the anti-propeller or flywheel end to .