John Middlesworth wrote:
>
> On Thu, 27 Feb 1997, Ken Brown wrote:
> >
> > I've always wondered how a machine shop balances an engine. Do they treat
>the
> > crankshaft, flywheel, rods and pistons, etc as one clump of reciprocating
>mass
> > like you would when you balance a wheel?
> >
> > Just wondering what you get for the $ spent,
> > Ken Brown
> > TR250
> >
> On my four-banger, the balancing and reconditioning the rods ran around
> $200 (that also included resurfacing the flywheel). As I was told by the
> shop, the rotating parts (crank and flywheel) are balanced in a large
> machine that spins them. They then grind off metal to achieve the
> balance. The rods are all brought down to the exact same weight by
> grinding off metal and the same thing happens to the pistons. As far as I
> know, the pistons and rods are done completely separately from the rest of
> the parts.
>
> John Paul Middlesworth
One other refinement, so I'm told, is to weigh the rods end for end;
that is, support the little end while putting the big end on a scale,
recording the weight, and then flipping it and repeating the process.
The idea is to make sure all the rods weigh the same at each end. This
results in all the rods having very similar polar moments of inertia and
centers of gravity in the same position. All of this contributes to a
well-balanced engine.
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