Date: Mon, 16 Dec 1996 20:14:45 -0800
From: Mike West <mwest@cdsnet.net>
Subject: Balancing CR. Long n' short jugs

We covered finding the long and the short pistons and rods in the
"Balancing" articles.
All being in the name of a "balanced" Compression Ratio.

Here's some more on the subject: "The long and short jugs".

Having finally recieved an hours clear sky, I painted my jugs.

Ala Hoover, tho I used paint thinner in lieu of gasoline.

Then they sat on the oil heater for a week drying.

It's cold and damp here so pay no mind to drying time.

In sitting here looking at them, it occurred to me that they represent
another stack of tolerances in the continued quest for the perfectly
balanced CR.

In fact, there is another stack out in the shop on the case where the
jugs sit.

The distance the spigot is from the center of the crank.

The guy had to have some tolerance to work from, + - .005", .001, who
knows?

So there is a long and short spigot face also.

Getting back to the jugs, I "miked" them.

There's a + - .005 on them too. One as low as 4.430" and one up to 4.440".

The other two are in beetween.

It's not much again but it can help with the stack-up of the pistons
and rods.

It also might be worth-while to put the closest matches together since
any difference will be a tweak in the heads when they're bolted on.

On the spigot faces, I'd hate to start messing with that, tho it could
be done. A little grinding could change them some.

The caveat there tho, is what if you stick another set of jugs in later and
the numbers run the other way?

Looking at these volumetric balances:

Assume a .005" difference on a stock jug of 85.5mm diameter.

Running thru the numbers, that equates to .7 CC.

That isn't too bad for the balance we're looking for but when it does
the same thru four parts and gets into the .020" (.5mm) then you're
looking at a couple, three, CC's. Plus the + - .5 CC you left in the
combustion chamber.

Any of it is livable but if you don't have to have it, why do so?

Where do you draw the line on this stuff?

Assume you have a car entered in the Baja 1000.

How far will you go to get reliability and performance?

The car won't see a repair shop for a thousand miles, or is it kilometers?

Now assume you're "Jane Average" with 2 kids and just drive back and
forth 30 miles to work every day.

The car needs tires but Billy needs a doctor.

That Baja racer will see complete refurbishment long before Janes
"daily driver" will see an oil change. So who's the long distance runner?

What about mileage? Does the racer with a sponsor need better gas
mileage than Jane? She doesn't have a sponsor. "less you count food
stamps.

Every dollar spent for gas is money the kids can't eat.

You get my drift here.

So let's look at important from the point that it has to be running
again no later than Tuesday.

Balance the weights of the components and get the CG's of the rods
the same. Take a look at the combustion chamber and keep it under
1 CC difference.

After that it's all relatively minor improvements and tho the "beater"
should have the best, the world doesn't work that way.

In fact you really want to save some gas, re-build that howling
transmission. That noise is horsepower leaks.


west