engine balance (updated)

[1968galaxie]

From my research:

"Most stock street engines will run smooth enough if they are balanced to 1 oz. (28 grams), although many late model engines have much tighter factory specifications (as little as 4 to 6 grams). For a high-revving performance application, aim for the recommended 2 grams or less."

Which category would your engine be?

[jayb]

Run it, Jim.  My big SOHC ran with one rod 10 grams out of balance compared to the rest, went out the back door at 7500 and I never felt any kind of vibration.

[Jim Comet]

Thats what R&R suggested also. Thanks, Jim

[pbf777]

I brought my 2 new Molnar rods to the machinist...........................

      So  along with the damaged pistons the two rods were bent?   

      Scott.

[Barry_R]

Most balance guys (including me) will add in some fantasy number to the bob weight for "oil".
I have seen everything from "0" to 7 grams.
Nobody knows why we do that or what the proper value is/should be.
Sometimes we just do stuff to a target that the machine can provide - even if the target is way beyond the actual need.

A long way of saying "run it"...

[Tunnelwedge]

15 grams for the oil. That's about 15 milliliters so about the volume that would fit in the crank.

[cjshaker]

15 grams for the oil. That's about 15 milliliters so about the volume that would fit in the crank.

I believe they are referring to the crossdrilled steel crank, which holds more oil than any of the other cranks due to it's hollow pins and dual feeds.

[Barry_R]

And check out that 750+ gram piston!
...and you wonder why they had rod/rod bearing problems back then....

[pbf777]

And check out that 750+ gram piston!
...and you wonder why they had rod/rod bearing problems back then....

        For the 429 marine application engines of the '70's, these were a forged, one valve relief, flat top, and with pin weight-in at between 950 and 1050 grams!   

        And to go with the "in-period" heavy pistons, check out the mass of the "NASCAR" rods (427), but then if we crossover to the BOSS 429 "NASCAR" rod examples all one can say is...............wow!

        But not to leave out the "Small Block" guys, take a look at the "Trans-Am" BOSS 302 rods, their pretty beefy, for something with a 5.315" center to center length, often weighing in at the upper realm of seven hundred plus (750-780) grams each.   

        Scott.