LEGO Fake Engines

Overview
LEGO fake engines, as incorporated into official LEGO sets never operated under their own power. They were created to mimic the mechanical movement of the piston-cylinder assembly of a real reciprocating engine.

Square Piston Fake Engines
LEGO fake engines first appeared at the dawn of Expert Builder sets when the 853 Auto Chassis set was released. The piston was square and required a brick-made cylinder assembly along with a Technic connector that clipped in the underside of the piston part.

Round Piston Fake Engines
The most popular kind of LEGO fake engine is the round piston fake engine known for its yellow colored pistons appearing in numerous Technic vehicles. It is one of the most popular types of engines to feature in many car MOCs made by LEGO fans today.