In a two-cylinder, horizontally opposed engine, the pistons are timed so that one fires on one revolution of the crankshaft and the other fires on the next revolution -- so one of the two pistons fires on every revolution of the crankshaft. This seems logical and gives the engine a balanced feeling. To create this type of engine, the crankshaft has two separate pins for the connecting rods from the pistons. The pins are 180 degrees apart from one another.
The difference in the 1300 engine is that the crankshaft has only one pin, and both piston rods connect to it. This design, combined with the V arrangement of the cylinders, means that the pistons cannot fire at even intervals. Instead of one piston firing every 360 degrees, a single pin engine goes like this:
* A piston fires.
* The next piston fires at 315 degrees.
* There is a 405-degree gap.
* A piston fires.
* The next piston fires at 315 degrees.
* There is a 405-degree gap.
And the cycle continues.
At idle, you can hear the pop-pop sound followed by a pause. So the sound of the 1300 is pop-pop...pop-pop...pop-pop.
