Harmonic balancer ?'s

[atomicjoe23]

I hopped on the auto parts website yesterday and the website described the harmonic balancer as neutral balance?

What exactly does that mean?

I know there is an externally balanced and an internally balanced harmonic balancer (referring to how the engine is balanced). . .I am assuming that "neutral balance" is referring to one of the two, but I don't know which one.

This is for a mid 70's 350 SBC ('75 Chevy K20 4x4). . .speaking of is this engine internally balanced or externally balanced?

Does the diameter of the balancer really matter? I see several different varieties available. . .6" 6 3/4", 8", etc.

I would like to replace the balancer on this engine because it's pretty old and I'm replacing pretty much all the other external parts on the engine so I might as well replace the balancer as well.

Thanks for the help!

[trkklr77]

neutraly balanced is internaly balanced.

the crank, rods, and pistons are all balanced in such a way that no other outside device is needed.


400sbc, 454, and 1987{?} + 350 are externaly balanced.

if you ran the motor with no flywheel or balancer it would shake like hell.

[Grumpy_old_fart]

in all actuality, based on the crankshaft design of every 350 that left the factory from 1968 to 1984, the 350 is externally balanced to some degree.

ok... i opened a can of worms, right?

wtf is grumpy thinking?

look at the rear end of the crank. you can see that there is some material added to the crank, vs. the early 283/327 round style cranks, this material make the crankshaft an internal balance... right?

the added material allows the use of a neutral balance dampner, just like the rest of the small block family with the exception of the 400. its still "internally balanced", in that it uses the same rotating parts subassemblies, like flywheel, dampner, etc. it is not the same as an early 283 in that the 283 was truly a neutral balance engine.

yeah, you can have a great discussion on this. the truth is right here, though... the extra weight added to the rear of a 350 is not on a 283, so.... it may be a neutral balanced engine... but cut that weight off, and you will have a requirement to balance it to a more fine tune.... like adding a bunch of mallory to make up for the lost weight.

[trkklr77]

if you cut a chunk of a 283 crank it will throw it out of balance just like your example.

just because its shaped differently dont stir up 3 dirrections of shit just because no one is agrueing yet.....



bitter young queef.

[Grumpy_old_fart]

Originally Posted by trkklr77

if you cut a chunk of a 283 crank it will throw it out of balance just like your example.

just because its shaped differently dont stir up 3 dirrections of shit just because no one is agrueing yet.....



bitter young queef.

yeah, thats me... just had to throw that wrench in there...

[MrWillys]

All 350's to the best of my knowledge are internally balanced, and use a neutral harmonic balancer. The 3.75 stroke 400 used the harmonic balancer, and flexplate (or flywheel) to balance the crank.
The balancer helps to minimize torsional forces applied to the crank when the cylinder fires.

Grumpy, I don't buy your disertation, because GM learned later that a bigger balancer helped to minimize these forces.

[atomicjoe23]

Thanks so far. . .now what about diameter of the harmonic balancer, does it matter? If there was a 6" on there before, does it need a 6" again, or will a 6.75" or 8" be OK?

[Grumpy_old_fart]

Originally Posted by MrWillys

All 350's to the best of my knowledge are internally balanced, and use a neutral harmonic balancer. The 3.75 stroke 400 used the harmonic balancer, and flexplate (or flywheel) to balance the crank.
The balancer helps to minimize torsional forces applied to the crank when the cylinder fires.

Grumpy, I don't buy your disertation, because GM learned later that a bigger balancer helped to minimize these forces.

when GM went to the one piece rear main seal motors, they did away with the added weight on the rear of the crankshaft, requiring a flexplate with a balance pad welded on. can you tell me why that is?

seriously.... I am interested.. oh, and it is still a neutral balanced engine as far as the dampner goes, so why a weighted flexplate or flywheel?

Im thinking the weight removed from the rear of the crank had something to do with that.

Originally Posted by atomicjoe23

Thanks so far. . .now what about diameter of the harmonic balancer, does it matter? If there was a 6" on there before, does it need a 6" again, or will a 6.75" or 8" be OK?

either will work.

[atomicjoe23]

Thanks that's what I thought, but I just wanted to make sure.

[MrWillys]

Originally Posted by Grumpy_old_fart

when GM went to the one piece rear main seal motors, they did away with the added weight on the rear of the crankshaft, requiring a flexplate with a balance pad welded on. can you tell me why that is?

seriously.... I am interested.. oh, and it is still a neutral balanced engine as far as the dampner goes, so why a weighted flexplate or flywheel?

Im thinking the weight removed from the rear of the crank had something to do with that.

With the weight of the flywheel, or torque converter why would additional weight be needed? I believe the weights you are refering too are for balancing.

To the OP: Larger harmonic balancers are for higher RPM usage. Just make sure you use one with the proper timing mark for the timing tag. 68 to 69 was a very slight change, and once again at least when they went to the straight up mark towards the left. Always check this when building a motor.

[atomicjoe23]

Thanks Mr. Willys

[madisonjam85]

Originally Posted by MrWillys

To the OP: Larger harmonic balancers are for higher RPM usage.

I think you got it backwards. A larger balancer is going to make the accessories spin faster.

[MrWillys]

Originally Posted by madisonjam85

I think you got it backwards. A larger balancer is going to make the accessories spin faster.

Feel free to explain how the balancer changes the size of the pulley?

[madisonjam85]

Originally Posted by MrWillys

Feel free to explain how the balancer changes the size of the pulley?

Never mind

[Cooter!]

I hope I don't regret asking, because it seems you all know quite a bit more than I about this subject... But here goes:

Wouldn't a larger balancer be more affective in a LOW RPM application? I'm thinking lever arm here...

Where a small diameter harmonic balancer would be more effective (faster reaction) in a HIGH RPM application?

I'm sure there are proven examples, I just can't get myself to google "NASCAR" tonight

[MrWillys]

Cooter,
The concept of the harmonic balancer is to minimize vibration created by lateral loads placed on the crankshaft from the firing of the cylinders.
You're thinking about maintaining momentum I think. My dad used to tell me stories about 90 lb flywheels on Dodge straight 6's when he was a kid in the 50's. He said you'd rev it up, let the clutch go, and it would go forward or break something. This would later be debunked by taking power away to spin the rotating mass.

[Cooter!]

I understand what the harmonic balancer does, and indeed it is the momentum of the outer ring (technically the TIMING of that momentum shift) that makes the damping affect.

I was thinking a smaller diameter damper ring (6") would react faster to vibrations than a large (8") one. At a higher RPM, aren't the vibrations at a higher frequency because the "power stroke" is happening more often?

Conversely, a low RPM, high torque engine would require more mass (8" diameter") to dampen the bigger force (torque) but also react slower (low RPM)?

[MrWillys]

Chevy took all these factors into account when it spec'd harmonic dampers. A forged-crank 283 had little more than a harmonic balancer hub, while those 283s equipped with a nodular iron crank had a real 63/4-inch (not 6-inch) balancer. Low-performance 327s tended to use the smaller 63/4-inch balancers, while the high-performance or Corvette motors (because they were driven aggressively and at higher rpm) used 8-inch balancers. Nearly all 350s came with an 8-inch balancer because of their relatively long stroke. An 8-inch balancer was used on the short-stroke, 3.0-inch-stroke, 302 Z/28 engines because those mills were intended for road racing. The 400 small-block, with its 3.75-inch stroke, used a unique 8-inch balancer with external balance weights. Also, as a group, trucks tended to use the larger balancers because they were intended to carry cargo loads or be used for towing, operating cycles that over time impart extended stress on the engine's bottom end.

[Cooter!]

Originally Posted by MrWillys

Chevy took all these factors into account when it spec'd harmonic dampers.I'm sure they did, to the tune of millions!
A forged-crank 283 had little more than a harmonic balancer hub, while those 283s equipped with a nodular iron crank had a real 63/4-inch (not 6-inch) balancer. Low-performance 327s tended to use the smaller 63/4-inch balancers, while the high-performance or Corvette motors (because they were driven aggressively and at higher rpm) used 8-inch balancers. Not really sold on the "high RPM" reason
Nearly all 350s came with an 8-inch balancer because of their relatively long stroke.That makes total sense
An 8-inch balancer was used on the short-stroke, 3.0-inch-stroke, 302 Z/28 engines because those mills were intended for road racing. My favorite V-8 ever
The 400 small-block, with its 3.75-inch stroke, used a unique 8-inch balancer with external balance weights.Because it's an externally balanced motor, and the flywheel had weights too
Also, as a group, trucks tended to use the larger balancers because they were intended to carry cargo loads or be used for towing, operating cycles that over time impart extended stress on the engine's bottom end.And also makes sense....

So other than the early 'vette 327, and the rare 302, my (wild guess) theory holds true? The stroke would have the biggest effect, more so than the total cubes of the motor.
Perhaps the anomalies can be explained by the RPM band the balancer is tuned for.

Also, I had to laugh at the old-skool 90lb flywheel story, an off-road mag just did a story on a bolt-on flywheel weight for 4cyl jeeps, claiming it "added torque". Might as well put on solid driveshafts and fill the tires with lead! Then it would be a monster

[trkklr77]

side bar here.

the 4cyl jeep had the longest stoke of any light duty truck/car ever made. 4.75". but they made shit for power. the heavy flywheel keeps that mass moving and from being stalled out from a gutless no power maken pos.

[oldenginebuilder]

Never before thought of it from Grumpy's perspective, but he is technically correct.

[Cooter!]

Originally Posted by trkklr77

side bar here.

the 4cyl jeep had the longest stoke of any light duty truck/car ever made. 4.75". but they made shit for power. the heavy flywheel keeps that mass moving and from being stalled out from a gutless no power maken pos.

That I agree with^^^^

It's the claim they made that the heavier flywheel creates more torque... From mystical unicorn hoof dust I guess.

[MrWillys]

Originally Posted by oldenginebuilder

Never before thought of it from Grumpy's perspective, but he is technically correct.

Which claim are you supporting Old Engine Builder? That 350's (68 to 85ish) are technically externally balanced due to the shape of the flywheel flange? Then, all large journal cranks should be included, because the 327, and 302 steelies are not round either. I believe this is offset in the counterweights.
Or, are you supporting that the weight (I think is a balancing weight) on a one piece flexplate is an external balance weight?

Discussion topic, and not trying to be a dick. I also believe that added thinkness to the one piece flexplate is due to the reduced flange bolt diameter.

[trkklr77]

the crank is an internal component.

[Cooter!]

This^^^^

And I saw that argument earlier about the crankshaft and thought it was a little dumb.

The facts are that almighty Chevy calls them "internally balanced", or in the case of the SB400 "externally balanced". That's good enough for me

Say what you will, I wear a Bowtie