Re: Internal vs. External Balance

From: John Dunlap (
Date: Sun Feb 28 2010 - 13:01:02 EST

Internally balanced engines are balanced genrrally two different ways.
One is static balance, where all the pistons are machined on weight
padd which are cast into the pistons. All are machined to the weight
of the lightest piston. The same is done to the rods. Then they are
assembled with rings and bearings in place, reweighed and the process
is repeated. Crankshafts are genrrally balanced from the manufacturer.
They have weight pads also that have extra weight removed as needed
due to being weighed on a spin machine, so that the crank doesn't
have too much weight at some counter balance weight pad than at
another. Generally that is as far as most shops will do. Racers prefer
a little more exact balancing thsm that and their devices/machines
that cal and will balance the entire spinning assembly including
harmonic balancer and flywheel/torque converter. You shouldn't have to
rebalance the sponning assembly when replacing torque converter or
harmonic balancer on a street engine as these are spin balanced to
themselves from manufacturer. Does that help ?
Sent from my iPhone

On Feb 28, 2010, at 10:15 AM, Gary Hedlin <> wrote:

> If your kit was balanced, then you don't need to balance it
> externally. Usually the kits have each piston and rod numbered and
> the builder puts them in the corresponding cylinders.
> I should say this... When I was selecting my components for my 340, I
> knew it was balanced externally FROM THE FACTORY. But since I was
> having it rebuilt with new pistons and rods, I spent a little more to
> have everything balanced to save the hassle of having it balanced
> externally.
> Usually when they externally balance an engine they use counterweights
> on the torque converter or harmonic balancer. But if you're going
> from a external balance engine to an internal balance engine, you'll
> need new ones that are neutral balance.
> But I think since the 360 was internally balanced, you shouldn't have
> anything to worry about.
> Gary
> On Sun, Feb 28, 2010 at 2:36 AM, Jamie Calder <>
> wrote:
>> The 408 "kit" was sold to me as a balanced kit. Does that mean it
>> should
>> have been internally balanced?
>> Still curious how this is done exactly. I know the spec sheet of the
>> pistons state the weight of each one (all 524 - 526 grams).
>> Are 360's externally balanced with the balancer or converter?
>> If a 360 needs a new harmonic balancer or torque converter, how do
>> they
>> determine where counter weight are placed and where do they go?
>> Thanks again,
>> James
>> --------------------------------------------------
>> From: "Gary Hedlin" <>
>> Sent: Saturday, February 27, 2010 11:28 PM
>> To: <>
>> Subject: Re: DML: Internal vs. External Balance
>>> Usually an engine that's been worked on has had the internals
>>> balanced
>>> (rods,pistons, crank) prior to assembly. An external balanced
>>> engine uses
>>> counterweights on the converter or harmonic balancer. Most of
>>> the time...
>>> Unless the engine builder is a complete idiot (experience from a
>>> 340
>>> project Im working on).
>>> Gary Hedlin
>>> Sent from my iPhone
>>> On Feb 27, 2010, at 8:41 PM, "Jamie Calder" <>
>>> wrote:
>>>> How are internal rotating assemblies balanced?
>>>> And external?
>>>> Can a visual inspection clearly tell weather a 408 short block is
>>>> internally or externally balanced? (got to answer some ebay q's)
>>>> Thanks,
>>>> James
> --
> Gary Hedlin
> 98 Sport 3.9 (for now)
> 05 SLT 4.7
> --Many talk about those who died, but too few talk about those who
> survived... THANK A VET!

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