wrote:

An old friend of mine is now managing a hi tech machine shop [turbocam
India] not too far away that is about to buy a balancing machine, and
he wants to help.

I need to do the preliminary work at a local shop first, including
making the bob weights; but are they 1;1 in this case [equal to
piston/rod assembly] or does reciprocating weight have to be worked out
separately like on a V8?

The principle is very easy:
Compensate all rotating masses fully
Compensate translating masses partial (50%, depending on application)

Rotating masses a
Masses on the crank shaft that are out of center. - crank + crank pin
rotating part of connection rod

Translating parts:
translating part of rod
piston, piston pin, piston rings

How to get the rotating mass of the rod:
It is very easy. put the top end of the rod (right where the pin is
going through) on a knife, the other end on a balance. What you read is
the rotating wheight. Reverse the setup (top end on balance) to get the
translating wheight.


Every mass that is out of center of rotation has to be compensated with
a mass that has the same distance*mass product. Say the crank pin
weights 0.1kg and is 25mm off center. The product is 2.5mmkg. You can
compensate it with a mass that is 50mm (CG) off center and weights
0.05kg Do that with all rotatning masses.
The translating masses are calculated with a distance half the stroke
and 50% of their mass.

The 50% can be varied. It depends on how the cylinders are arranged
(horizontal/vertical) and if you prefer vibrations to be horizontal or
vertical. Bikes normaly have vertical vibrations. Compensation is going
up to 70%.
Assuming translational masses are 0.3kg, stroke is 50mm and you want a
60% compensation, you get:
0.3kg * 50mm/2 * 0.6 = 9mmkg.

Now if you add all compensation masses you have to select a mass who's
CG offset and whos mass is the same product. Counterweights normaly do
have a D-shape. It takes some math to find the CG. Better to use a CAD
for that.


HTH. If I was to confusing, feel free to ask.
Nick

--
Motor Modelle // Engine Models
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