RE: boxer motors

[White Anthony <anthony.white@xxxxxxxxxxxxxx>]

James Tyson wrote:
> Paul M.'s post indicated that the terms "boxer" and "flat" were synonymous.I 
> have been laboring under the impression for some time that a flat,or 180 
> degree engine doesn't have to be  an opposed or boxer engine.Could someone 
> please educate me on this subject?

There are some situations where an engine with horizontally opposed pistons isn't designated a 'boxer'.  Perhaps a Scotch Yoke Engine, while ostensibly a boxer, deserves a different designation (see: http://www.cmcpower.com/html/howitworks/howitworks.asp# ).  Also, there were some Comer two-stroke diesels in the fifties and sixties that had two horizontally opposed pistons in the same cylinder with their crowns facing each other, but with the combustion chamber between the pistons (see: http://www.topolino.demon.co.uk/ts3.htm ).

Aside from the above exceptions, it's usual for 'boxer four', 'flat four', and 'horizontally opposed four' (or six, or whatever) to be synonymous.  But while 'boxer' or 'horizontally opposed' are more technical designations, 'flat' could also be a spatial designation, meaning simply that the engine is not very tall.  Certainly there have been circumstances where manufacturers have laid straight fours virtually on their sides for space reasons, and referred to them as 'flat' -- the Toyota Previa minivan had a straight four engine, laid nearly flat in this latter sense, and referred to as a flat four cylinder engine in some of the sales material, and in some of the motoring press with less of an engineering orientation.      

Inevitably , there will be others out there who can think of other examples.  

Regards,
Anthony.  
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