Internally balanced something

[GTRS Fiero]

Trying not to clutter the other thread.

My understanding is that the engine block is the same for both the internally balanced engine and the externally balanced engine.  Further, my understanding is that the crank is what is or is not balanced.  Since the crank balance weight is internal to the engine, I guess that is where the term originates.

Isn't it actually the crank that is or isn't balanced?

[Fierofool]

That is correct.  Balancing takes place on the crankshaft where drillings are made into the counterweights. 

The blocks for all Fiero V6's aren't the same.  The 87 and 88 engines had modifications to the oil galleys.  I believe they larger to provide better oiling.  There may be other differences, too.  This summit article mentions that converting an externally balanced engine block to an internally balanced engine might require modifying the block for clearance of the larger counterbalances usually found on an internally balanced engine's crankshaft. 

https://help.summitracing.com/app/answers/detail/a_id/4878/~/what%E2%80%99s-the-difference-between-internal-and-external-engine-balance%3F

[GTRS Fiero]

Hmmm.  As far as the crankshaft goes, I thought the balanced crankshaft had been swapped, which seemed odd, because GM initially said there wasn't room to balance the crankshaft.


Yes, I remember the oil galleys being different.

[Fierofool]

I'm not quite understanding.  Balance crankshaft had been swapped?  Not room to balance the crankshaft?

The counterweights on an internally balanced crankshaft are larger.  Weight is removed from the counterweights by drilling into them.  Nothing is added to them. 

We used to balance the rods and pistons of some of the VW engines we put into the kit cars.  It's a tedious job, finding the lightest piston and lightest rod, then removing just enough metal from them to make them all match.  Balancing matching big and little ends of the rods is the most time consuming.  If you should take too much from one, then you must go back and reduce the others that you may have already finished. 

Externally balanced flywheels and flexplates get a generic weight welded to them, or sometimes the extra weight is cast onto the flywheel.  Then metal is removed around the perimeter, outside the cutch plate contact surface, to make the balance.

[GTRS Fiero]

My understanding was that weight was added to the crankshaft.  There was an image of the larger weight on an '88 crankshaft, compared to a pre'88 crankshaft.  I may have misunderstood.

[scottb]

the counterweights are slightly bigger, then the factory drills a pocket to remove mass to bring it in to balance. It is the opposite of balancing a tire/wheel, where the weight is added. I have heard of adding weight to a crankshaft to balance it but that is a more specialized application. And much more expensive.

[GTRS Fiero]

Here is one comparison of crankshafts.