Date: Thu, 17 Feb 2005 08:42:35 -0500 From: "doug" <dougejNOSPAMnospamFREEhotmail.com> Subject: Re: new saab motor for 9-3 series
Your comment is one of the few cogent ones in this entire thread regarding the inherent smoothness of an inline 6-cylinder design. It has both primary and secondary balance. Primary balance is when the crankshaft counterweights offset the weight of the piston and rod. Secondary balance is when the movement of one piston balances the movement of another. V6's have a secondary imbalance that causes engine vibration. Adding a counter balance shaft can reduce this imbalance, but that adds weight and complexity. An inline four engine also has problems with secondary vibrations. The cylinders are unbalanced for secondary forces, not moments. Therefore, instead of trying to rock back and forth the inline four-cylinder engine tries to "hop" up and down on its mounts. "Everett M. Greene" <mojavegnospamveg.iwvisp.com> wrote in message news:20050216.7A412A0.8489nospamveg.iwvisp.com... > Dave Hinz <DaveHinznospamcop.net> writes: > >> And the dual balance-shaft design of the I4 is very >> vibration free. > > So that's how they do it. > > I read somewhere many, many years ago that a 6-cylinder > engine (in what configuration, I don't recall) is > inherently balanced whereas a 4-cylinder engine is one > of the worst, if not the worst, in trying to get it to > run smoothly. My experience over the years has found > this to be at least approximately true in that, other > than the Saab, the 4s have been rather rough running > while the old Corvair and the 6-cylinder Porsches > run quite smoothly.
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