At 02:32 PM 2/12/2000 +0200, you wrote:
>Hi all,
>
>I took my crank, flywheel and balancer to Zimbabwe to be ground, hardened
>and balanced but they don't know the "formula" for balancing the 302. Do any
>of you know? This guy seems to know his stuff but says that he needs to know
>the size of the weights to clamp onto the big end journals to do the
>balancing. If any of you know a good balancing shop, could you please get
>this information for me....
>
>He can do a static balance but I fear this may not be enough and don't want
>to put my blood, sweat, tears and $ into an engine that is going to be a
>disappointment....
>Derek White
Derek,
Check out the following web site for the info on balancing
your 302:
<http://personal.mem.bellsouth.net/mem/m/a/maxxbhp/balance.htm>
The following is an extract from above if you can not connect. I
also added a few comments
of my own.
"Now, our old buddy the 90 degree V8. If you're a gearhead and you've never
worked on a V8, you're not from this planet. It is the staple of American
racing. There is some kind of complex cause and effect relationship that
makes us run V8's. In and among the many parameters of that relationship
lies the fact that V8's are very easy to balance, and run quite well out of
balance (relatively out of balance). 50% bobweight is the rule, with a 2%
overbalance on more serious engines. NEVER under balance an engine, meaning
don't let your counterweights be lighter than the bobweights.
OK, what the hell is a bobweight? It's a 2 sided metal canister with a
fitting that looks like a rod journal attached to it. After you weight
balance all your pistons, rods, etc., you use those weights to create a
bobweight using lead shot inside the metal canisters. Screw the lids down
tight onto the shot so it doesn't slosh around, and bolt it onto the crank.
Then put the crank, with bobweights, on the crank balancer and giv'er a
spin. Here's how to make a bobweight.
Weigh the big end of the rod, add the weight of the rod bearings, and
multiply this by 2.
Add together the weight of the piston, pin, locks, rings, and small end of
the rod.
Add those 2 numbers together, add 4 to 6 grams for oil, and multiply by 50%
(or whatever)
Put the bobweights on the crank, on each main journal, on the side opposite
the counterweight, and eyeball them square with the counterweight. "
My Comments:
Do not forget to bolt on the flywheel and damper for the balancing.
Could add the clutch as well.
Note that the "main journal" above should just say "journal". The
journal
is the bearing surface for the big end of the rod. You do not add anything to
the main bearings.
As stated above " After you weight balance all your pistons, rods, etc.,"
Take the lowest weight piston and balance the other 7 to match the weight.
This is usually done by drilling out a bit of the aluminum from supporting
structure for the piston pin inside the piston. If one has never done this
before, I recommend practice drilling on an old piston and weighing the
result to get a feel of how much to remove. Recommend using about a 1/2"
dia bit.
Weigh the rods and find the lowest weight, total as well as the small end
and the big end. Make all rods match weights in big end, little end and total
weight. There is a hunk of steel on each end of the rod that can be ground
to decrease the weight.
To weigh the small end of the rod, support the rod at the big end
with a "journal" that allows postive location and free rotation
of the rod. Support at the small end to weigh the big end.
Each rod should be supported exactly the same and the weights measured at
the center of the unsupported end.
The rings and bearings should match in weight already.
Use a precision scale that can read a delta weight of 1 gram to do
this work.
Keep your beer away from the machinest until he is done!
James Barrett Tiger II 351C and others
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