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wrote:
More than 40 years ago I had an automotive encyclopedia that gave good
definitions for both two cylinder engins and twin cylinder engines. I
loaned the book and never got it back.

As I remember, a twin cylinder engine had two pistons, rods, and shared
the same combustion chamber, while a two cylinder engine had separate
combustion chambers. I am probably remembering wrong, but know there
was a distinct difference.

I have Googled all the ways I can think of, but cannot find a
definition for a "twin cylinder" engine. Seems like the names have
become interchangable. Does anyone have a documented source for the
definition of the "twin cylinder" engine?

This has been driving me crazy for years.

Thanks,
Paul in Redmond, OR

The english language has never had an absolute authority to answer
questions like this. Even general use dictionaries are at odds on some
terminologies. It is very hard to define 'common usage' because various
groups may have different terminologies within their own groups. If SAE
says something about a definition, I'd tend to go with that. Does
anyone know if SAE ever published a 'dictionary of terms'?

As an example of the lengths that these arguments an go to, find a large
group and ask for definition of 'boat' vs 'ship'.