Which side is number 1 cylinder on?

That depends entirely on the engine! There's no universal standard for cylinder numbering. It varies by manufacturer, engine type (inline, V, flat, rotary), and even sometimes within the same manufacturer's lineup.

To know which side cylinder #1 is on, you need to:

* Consult the engine's service manual: This is the definitive source.

* Look for markings on the engine itself: Manufacturers often cast or stamp the cylinder numbers directly onto the engine block or head.

* Use a diagram: A diagram of the engine will show the cylinder layout and numbering.

Without knowing the specific make, model, and year of the engine, it's impossible to answer your question.