Should I balance the rotating assembly?

[Mossman747]

Hello all,

 

I am rebuilding a pair of 1960 Evinrude Lark IIs on my 18’ Lyman.  One powerhead has a bad crank and I am replacing it with a NOS crank and good used flywheel.  Should I have the crank and flywheel balanced as an assembly?  I am also considering balancing the piston/rod assemblies for a fully balanced rotating assembly.  Would this be worthwhile or would it not make an appreciable difference in a 2 stroke motor?

 

regards,

Mike

[frankr]

Good question.  Some of those 40’s were downright scary with vibration.  Once upon a time, back in “The Day” I attempted to balance one.  Maybe I didn’t know what I was doing (true), but the result turned out as bad or worse than the original.  Go for it if you want, but I wasted my time.

BTW, do you know the 1960 40hps had a problem with breaking crankshafts?  Obviously, they didn’t all break because thousands of them survived.

[Mossman747]

I’ve heard that about breaking cranks. The crank I’m replacing was actually ok except for the fact that a previous owner damaged the taper then aggressively smoothed it out with a file causing the flywheel to have about .050” of run out which caused  enough vibration to completely wear out all of the ignition and throttle linkage.

[Author]

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