Engine Balancing Questions

[smittyb]

I just picked up my parts from the machine shop, where I had my rotating assembly balanced for my new pistons. The balance shop included a card with some specs, and I was wondering if some one could tell me exactly what they meant. I understand the balancing proceedure, just not what they have written on the card. Reads as follows:
---------Grams removed --Finished
Piston---------.6----------- 506
Pin-------------0------------122.1
Rod recip------2.2-----------170.3
Rod rotate-----4.4-----------389
Bob weight-----------------1724.4

Crankshaft damper end
Orig unbalanc 87.5gr/in
Residual unbalance .2gr/in

Crankshaft drive end
Orig unbalance 126 gr/in
Residual unbalance .1gr/in
Can anyone decipher this for me? Thanks
Edit: My formatting didn't quite work, the first number is in the removed column, and the second number is in the finished.

 

[smittyb]

Nobody?

 

[86bluecobra]

try giving rick 91gt a PM he is an engine builder and i bet those numbers would mean something to him.

 

[smittyb]

NEbody else?

 

[fidstang]

They way I understand it is they take the lowest weight from the pistons and rods. Then remove material from the others to match the lightest rod or piston. Then they wiegh them together- rod, piston, pin, bearings. This gives you the bob wieght. They remove material from the crankshaft to counter the wieght of the rod/piston assem. Thus, reducing unwanted harmonics at a certain RPM. (bad vibrations) As for the crankshaft unbalance info. I am not sure. I would guess it is the amount of material they took out and the corresponding areas,Front(damper end or the flywheel end). I am just guessing. Only a real engine builder knows.

 

[rd]

In overall terms it is the weights that were recorded for you parts.

---------Grams removed --Finished
Piston---------.6----------- 506 Amount removed and actual weight of piston in grams.

Pin-------------0------------122.1 Weight of pin

Rod recip------2.2-----------170.3 Amount of weight removed and remaining weigh of the piston end of the rod.

Rod rotate-----4.4-----------389 Amount removed and remaining total weight of the crank end of the rods.

Add the two rod weights together and it should be the total weight of the rod.

Bob weight-----------------1724.4 This is the amount of weight they put in the bob weight cannisters on the crank to simulate the pistons and rods. I would have to look up how to calculate it.

Crankshaft damper end
Orig unbalanc 87.5gr/in
Residual unbalance .2gr/in These are the weights involved at the damper end of the crank.

Crankshaft drive end
Orig unbalance 126 gr/in
Residual unbalance .1gr/in These are the weights for the rear of the crank.

Sounds like it was done pretty nicely.

 

[smittyb]

Thanks rd, That's pretty much what I was looking for, but the numbers that intrigued me the most were the "unbalance" ones. I was really curious as to what original and residual unbalance meant. Like, for instance, if I hadn't of had it balanced, what it have been 126 gr out of balance? Thats freakin crazy.