'77 balance question

[EffinDuff]

In my journey of fixing all the ghetto rigged stuff on my 72 from the previous owner i came across this balance hole in the crankshaft.  This is a 77 400 block.  I do believe it was rebuilt to factory specs (still has 3mm piston clearance to deck) and runs like a pig.  My understanding was that these motors were externally balanced which meant weigths were put on the flywheel and different harmonic was used to balance the motor.  Am i correct in thinking this?  If so would there be any rhyme or reason to having this hole in the crank and how would it affect the car if there are weights on the flywheel?  On a side note does it matter that the balance hole ripped through the sidewall like that?

[EffinDuff]

Thanks in advance for any help with this!!  Oh and by flywheel i mean torque converter its an automatic... It's late and i'm tired haha  .

[firefighter3931]

  My understanding was that these motors were externally balanced which meant weigths were put on the flywheel and different harmonic was used to balance the motor.  Am i correct in thinking this?  If so would there be any rhyme or reason to having this hole in the crank and how would it affect the car if there are weights on the flywheel? 

Cast crank motors are all externally balanced.....what you're seeing is normal. The hole in the counterweight is there to help with the balancing and is OK....nuthing to worry about. Make sure you have the proper dampner and tq converter or it will vibrate like crazy. 



Ron

[EffinDuff]

Ron you are the man.  Much appreciated. 

[Chryco Psycho]

Balance holes in the crank were there to get the balance cose to where the external balance will work

[EffinDuff]

Thanks Chryco Psycho.  I was not too sure with everything else i have seen wrong w/ this motor so i figured i would check.  And to further bug me we are getting a rather bad shake but I am 80% positive it is from the drive shaft.  Set up a runout guage and checked the driveshaft and it was off.  On top of that we put the front of the car on ramps and jacked the ham up in the rear to simulate ride height and load.  Then spun the tires and around 28-3100 rpm the car has a nasty shake and the driveshaft is all over the place.  I read another thread in here that suggested to run the motor in neutral to make sure it is not out of balance.  We did that and the motor ran through the revs fine.  When we jacked the rear up we sat the housing on jack stands to even out the load and had the jack under the ham juust incase.

This approach may have been completely wrong but i am sure someone will not hesistate to say nice try but no haha.   .