This project is a homage to one of the first LEGO sets I ever purchased, Auto Engines 8858-2.
The idea behind this set was to make a modular engine system that would allow for a variety of engines to be constructed using a base set of parts, similar to the set that inspired it.
I have example here of a inline 4 engine, 4 stroke, properly timed (valves and cylinders working with intake and exhaust valves timed with the working pistons).
I designed the motor to be easy to mount in both traditional 'system' attachments as well as pin holes for mounting and interfacing with Technic elements.
Below is a video of the engine running using an optional motor.