Y2K SS

iTrader: (1)

Engine that is. Feel like a dork for asking this. I built a fully forged 383 in my garage that rips and I never got a straight answer on this.

slow3hoe2

iTrader: (3)

internal balance...the crank is balanced to itself, so the dampener and flywheel have no counter weights on them.

external balance...dampener and/or flywheel has counter weights to complete the balance of the rotator.

hopefully that made sence

Y2K SS

iTrader: (1)

OK so my LT1 is externally balanced and my LS1 is internally.

slow3hoe2

iTrader: (3)

that sounds right...but im not sure. im not to familiar with the internals of those engines.

ktmrider

That is right...the GenIII is internally balanced. One way to tell is that there is no woodruff key on the crank snout. Means the "balancer" is now just a belt drive, not a harmonic dampener.

Y2K SS

iTrader: (1)

ok so what do you make of the flywheel?? The reason I ask is I had the pressure plate balanced to the flywheel and the machinist who balances all the motors told me that the flywheel is not balanced it is spec'd to engine. He said that no late model chevys are internally balanced. He put the flywheel and the machine and sure enough it was not balanced but yet there are numeous holes drilled on one side to show an attempt to some kind of balancing.

slow3hoe2

iTrader: (3)

if an engine is 100% internally balanced, the flywheel and dampener need to be 0 balance.

ktmrider

My understanding was that the dampener/pulley and flywheel/flexplate are balanced individually from the internal rotating mass. Theoretically it would work, especially for the flywheel. The pulley/balancer has no keyway for alignment so installing it in the exact same place or orientation would be difficult.

9C1/B4C

"internal balance...the crank is balanced to itself, so the dampener and flywheel have no counter weights on them.

external balance...dampener and/or flywheel has counter weights to complete the balance of the rotator. "

That part is right, but then there is dynamic balancing in which all the parts are balanced together to make up for production weight tolerances. All Chevrolet (and likely all other manufacturers as well) engines are dynamically balanced. This dynamic balancing (done by adding or removing weight from either the HB and/or flywheel) makes those parts unique to each engine assembly, and makes it necessary to reinstall them in the same orientation they were originally - whether there is a keyway or not.

YsoFast

Ok now I am confused. If GM dynamically balances and I am building a new engine that has had the crank balanced by its self does this mean I need to have all the other parts 0 balance? It seems to me that I would but then again I am putting a Ram VDS clutch in and an under drive crank pulley in. Shouldn't they already be balanced?

Y2K SS

iTrader: (1)

when you get your engine balanced they will ask for the dampner, and flywheel and they will balance it as a whole. At least that was what they did with my stroker last year.

As far as 9C1/B4C goes...THANKS man....finally its explained the way I needed to hear. Thats what the machinist was talking about then. So all these guys saying to zero balance the flywheel before putting it on aint right then???

slow3hoe2

iTrader: (3)

if an rotating assembly is truely internally balanced...there is no need for the guy balancing it to have the flywheel or dampener.

zamboxl

iTrader: (1)

so wait if you put a new flywheel on it needs to be balanced to the engine????? do they already come balance or what??

Y2K SS

iTrader: (1)

that's the thing.. everyone says they are internally balanced but they don't appear to be. Go and look at a stock flywheel, there might not be any weights on it but if you look on the engine side of it you'll see holes drilled on parts of the flywheel. But if you go and put it on a machine you'll see it's not balanced. Mine was 12 grams off. So if its altered to be unbalanced obviously the motor itself isn't.

Zamboxl.... I would just stick to OEM flywheels. My machinist told me that being slightly off balance its not going to hurt anything. There are different levels of balance. There is never a perfect balance the only way you get that is with NASA in space. I think the best a machinist can get is to like level 2-3. The scale is like 1-5 or something.

9C1/B4C

The internal/external balance issue has nothing to do with the dynamic balance. I know for sure Chevrolet dynamically balanced all Gen 1 and LT1 engines. I can't tell you for sure about LS1s (I haven’t toured St. Catharines yet), but I would expect that they are also dynamically balanced. I know that there were different levels of balance (different accuracies, might be abetter term) for different applications. A Gen 1 passenger car engine was not as closely balanced as a Gen 1 Corvette engine. I once heard the inch/ounce numbers, but it was too long ago for me to remember.
If the old flywheel or harmonic balancer is intact, I believe the new unit can be balance matched to the old unit by a competent shop. Of course sometimes those parts are replaced because they are no longer intact, and I believe in that case balancing the entire rotating assembly is the only way to regain the dynamic balance. I suppose in some cases one might decide to gamble and see if it is close enough out of the box.