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V6 crankshaft balance factors. 1

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JKart

Electrical
Dec 22, 2005
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GR
Hello gentlemen,
I have a question regarding V6 crank balancing. The engine is a 60degree V6. I fabricated dedicated half-ring shaped counterweights which are fixed on the rod journals for dynamic balancing (there are no accessories available in my area for balancing V engines!). The weight was determined by the usual practice (100% rotating+52% reciprocating). Calculations were based on standard pistons. However, I now have a set of forged pistons, weighing ~20% less than the std items. If I calculate backwards using the reduced weight, it turns out that my balance factor is now ~58%. If I leave things like this, what negative effects (if any) can I expect? Is it absolutely imperative that I must use a factor from 50-55% and no more? All bits and pieces of literature on the subject point to the choice of balance factors being a 'black art'.
 
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The negative effect is that your crank is bit heavy. I wouldn't sweat.

Choice of balance factor is a black art, unless you analyse the crank in great detail. The correct approach is to minimise the main bearing loads in some fashion.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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