OK Here was an engine that still had some kind of connecting rods but not the same as standard engines: THE Bourke Engine.
I have a large report on the engine, it WAS built and run.
Here are some excerpts from this article:
Bourke-Engine : Bourke 30
And this from the article:
Bourke Engine Documentary - Bourke Cycle Edition
"The Bourke Engine Ran With A 50:1 Air/Fuel Ratio And Produced More Horsepower & Torque Per Pound Than Any Other Engine In History. It Had Only 2 Moving Parts, The Oil Never Had To Be Changed, It Was Very Quiet, And It Ran Very Cool. At nearly 70% thermal efficiency, it's the most efficient gasoline engine ever made!"
REVEALED: The most important gasoline engine ever made, where it came from, how it works and how to build one.
Sadly this page is also SELLING info on this engine so be warned.
None the less there is a ton of info in these pages…this could be very worthwhile looking deeply into these claims.
Rich