[Jay S]

Thanks for the correction Paul, that is correct the Arma is a trade name of nodular steel by GM. I just used it as an example because I consider it among the best of Nodular irons, kind of a bench mark.

I did mention the grain structure of the offshore cast cranks was pretty crappy. The metal is also softer. There is more too it that just yield numbers. Versus watching a big HP engine using a Pontiac OEM crank, I would place to hide if an off shore cast crank was used in a 800 HP+ engine dyno session!

The factory Nodular cranks Pontiac used are very tough, but not compared to a non twist 4340, that was my point, it was not too talk down Pontiac’s factory cranks. It probably sound like it the way I worded that statement. I have almost all N cranks, and one 4340 in my Pontiac cars. Like I mentioned or inferred in a couple other posts, I think the harmonic balancer destroys more factory cranks than over loading them.

Thanks Shiny, good catch, elasticity was not the correct wording, should have use resilience or toughness. Good thoughts.

[Jay S]

So this is a hypothetical question. Which I think was the original intent for Paul starting this thread because he runs into this all the time.

Your engine builder gives you 3 options, 600 HP street and strip Pontiac engine. Your on a budget. Which one do you choose?

1. A stock seasoned PMD 4.21 N crank, light weight internals, lightest of the 3 combos, H beams, stock type, slightly better “high performance” harmonic balancer.

2. A stock seasoned PMD 4.21 N crank, same pistons but heavier and cheaper I beam rods, very nice ATI race type harmonic balancer. H beams are swapped for I beam to upgrade the for the better balancer.

3. A new 4.21” 4340 crank, stock type dampener reused from the customers engine. It looks good, but it is 50 years old. I beams rods, a slightly heavier cheaper pistons because the crank ate up you budget!

Ah yes….this is how I end up with parts for 2 engines when we only intended to build 1, cause I changed my mind mid build…Lol

[Sirrotica]

I think the harmonic balancer destroys more factory cranks than over loading them.

From my own experiences I would agree that statement. Many times a faulty crank is blamed, but harmonics make that part fail rather than what it's made from.

If anyone here has ever observed a diesel engine at idle, and watched the fan belt in the area of the balancer, it is constantly changing speed as each cylinder comes up on compression, and then fires. That speed change is constantly trying to twist the crank forwards, and backwards. A diesel many times can be 22 to 1 compression, so it's roughly twice what a gasoline engine is. That's why it shows up at idle, and can be seen with the eye. Gasoline engines go through the same type of twist motions just at a lesser degree. This is one of the forces the the balancer tries to dampen. Take that dampening away, and material failure happens rather quickly. You'll find the weakest link in the chain

Just springing for a billet, or forged piece isn't any guarantee that the part will survive. The balancer will either lengthen the longevity, or if defective, will shorten the longevity of that shaft. Don't cheap out when it comes to what you hang on the front of that expensive crankshaft.

[Formulas]

PEARLITIC MALLEABLE IRON .... I remember reading about this type of iron in relation to Pontiac castings but i do not remember the specifics on exactly where and when it was used IE in our rods or crankshafts Arma Steel or N'cranks

[PAUL K]

Originally Posted by Formulas

PEARLITIC MALLEABLE IRON .... I remember reading about this type of iron in relation to Pontiac castings but i do not remember the specifics on exactly where and when it was used IE in our rods or crankshafts Arma Steel or N'cranks

P.M.I term used by the experts at H-O racing specialties to describe the material used for 64-69 Pontiac crankshafts.

[PAUL K]

Originally Posted by Jay S

So this is a hypothetical question. Which I think was the original intent for Paul starting this thread because he runs into this all the time.

Your engine builder gives you 3 options, 600 HP street and strip Pontiac engine. Your on a budget. Which one do you choose?

1. A stock seasoned PMD 4.21 N crank, light weight internals, lightest of the 3 combos, H beams, stock type, slightly better “high performance” harmonic balancer.

2. A stock seasoned PMD 4.21 N crank, same pistons but heavier and cheaper I beam rods, very nice ATI race type harmonic balancer. H beams are swapped for I beam to upgrade the for the better balancer.

3. A new 4.21” 4340 crank, stock type dampener reused from the customers engine. It looks good, but it is 50 years old. I beams rods, a slightly heavier cheaper pistons because the crank ate up you budget!

Ah yes….this is how I end up with parts for 2 engines when we only intended to build 1, cause I changed my mind mid build…Lol

Can I phone a friend

[Dragncar]

Originally Posted by Sirrotica

From my own experiences I would agree that statement. Many times a faulty crank is blamed, but harmonics make that part fail rather than what it's made from.

If anyone here has ever observed a diesel engine at idle, and watched the fan belt in the area of the balancer, it is constantly changing speed as each cylinder comes up on compression, and then fires. That speed change is constantly trying to twist the crank forwards, and backwards. A diesel many times can be 22 to 1 compression, so it's roughly twice what a gasoline engine is. That's why it shows up at idle, and can be seen with the eye. Gasoline engines go through the same type of twist motions just at a lesser degree. This is one of the forces the the balancer tries to dampen. Take that dampening away, and material failure happens rather quickly. You'll find the weakest link in the chain

Just springing for a billet, or forged piece isn't any guarantee that the part will survive. The balancer will either lengthen the longevity, or if defective, will shorten the longevity of that shaft. Don't cheap out when it comes to what you hang on the front of that expensive crankshaft.

I did not cheap out on mine. I paid 440$ for mine and now they are 663 $

Ductile iron, nodular iron and Arma Steel, all the same thing. Rods and 4 bolt caps made out of it too.


https://harmonicdampers.com/index.ph...1ule6u3li6m4f5

[Shiny]

Regarding harmonic dampers...

Do they have to be "tuned" to the rotating assembly or are they "universal" (within reason)?

My guess is if they are true vibration dampers, they won't care much what they are damping but then again, they are part of a system that's vibrating in torsion so the masses and stiffness of all the components will affect the magnitude, resonant frequencies, and intrinsic component damping.

For example, I expect a cast iron crank to dampen vibe better than a steel crank. Similarly, aluminum rods are a third the stiffness of steel or iron, which has to affect vibe response of the system...

Sorry for the diversion - just going down my overthinking adventure path and about ready to replace the 52-yr-old damper on my car so it kind of popped up.

Mike

[Half-Inch Stud]

Shiny, You are on to sometingk there.

Consider at idle, the Manual Flywheel assy, and the wee little Front Damper. The flywheel doesn't want to Accel (powerstroke), nor decel (compression stroke ), so the front damper accels and decels, thus indicating the crank is sprung into torsional flexure.

A manual flywheel assy at both end of the crank would surely place the peak torsional at the Middle of the Crankshaft. May not do much good for acceleration-based racing, but would sure help an aircraft engine deal with the super-high inertia Propeller. Is another reason why i prefer the TQ Converter over an iron Flywheel Assy.

I have wondered if a bigger dia damper is "always better" to help flywheel-through the Power and Compression strokes. Overall i think the much larger damper would shift the crank (flexure) failure to rod throws around #3-#4 Mains, and save #2 Main fatigue from being the 1st fail. Crankshafts with full counterweights sure help lower torsional fatigue from Power and Compression cycles, yet need balanced well to keep them weights from wafting from over-heavy or over-light pistion/rod bobs.

In you point, lightweight rods and slugs ought help the Stock size damper to dampen well, provided good crank balance.

[Shiny]

Trying to educate myself.. you guys know this stuff..

Article published on NHRA web site (here) says:

" A stock damper is calibrated for a specific power level and rpm range, and as you go beyond that point, the stock-bonded rubber damper becomes less effective and can fail with the damper coming apart. .... any engine that has been modified for increased horsepower and/or higher rpm limit can benefit from the use of a quality harmonic damper.”

If correct, then yes, stock dampers are "tuned" and changes to stock rotating assembly without addressing the vibe risk might be a contributor to crank failures.

I'm sure the damper sellers will agree but I'm now wondering when you guys justify changing from stock style to a $500 damper?

[25stevem]

I think we are not keeping in mind here that even the when using the lightest parts that are then balanced in the most precise manor that the balance job still can not compensate for the load / twist put into the crank by the on then off again massive power stroke and the increasing rate of that as rpms go up.

[Dragncar]

My old 455 just used a PMD balancer I had Whitmore check out and degree mark. I tried some Professional Products pile of junk for a bit and took it off. It moved around from the get go.

[Dragncar]

Fresh cut Crankshaft Specialist rod journal. You can see what they did in the corner.
Almost a smooth 45 deg corner vs a round radius.

[tom s]

Early HP factory balancers we’re actually dampeners,the issues with the HDs And SDs is over time the parts in them would rust and no longer dampen.They went to the 2pc bonded balancer.When a HP balancer was needed the outer ring was much bigger and heavier.Tom

[Half-Inch Stud]

Yes, and the 69 Sprint damper was a much larger diameter than baseline. And you know the Inline-6 crank was 2-CYls longer than the V8, and alot smaller Main Diameters, so it gott have twists going on.

[Jay S]

Originally Posted by Dragncar

My old 455 just used a PMD balancer I had Whitmore check out and degree mark. I tried some Professional Products pile of junk for a bit and took it off. It moved around from the get go.

I am not a fan of the PP balancer either, or really any of the 2 piece polymer bonded balancer’s that are bigger in diameter or heavier than stock for more harmonic control. For starters the heavier inertia ring is harder to keep in place. If it does fail, instead of a stock PMD dampener that was probably designed for around 3000 rpm, you now have a dampener that is designed for something closer to 4K, and when the elastomer fails, it is now allowing amplification of the harmonics instead of dampening them. Where you see the stock PMD harmonic balancer mostly breaking cranks in front of the number 2 main, now that same stress point is going to be further back on the crankshaft. When it fails(and they commonly do on heavy cranks) I think it ends up moving the worst harmonics closer to the center of the crank. When it does it’s job it will help over a stock unit, but if it fails it is worse than stock. I know lots of builder’s use those type of balancer’s on engines like a SBF or a SBC, but I think they really do not work very well on a nearly 80 lb PMD racing crank.

JMHO, I’d rather spend the more money for something that does it’s job better, and is lighter weight like an ATI or similar that has inertia rings inside the case of the outer ring.

[Dragncar]

Originally Posted by Jay S

I am not a fan of the PP balancer either, or really any of the 2 piece polymer bonded balancer’s that are bigger in diameter or heavier than stock for more harmonic control. For starters the heavier inertia ring is harder to keep in place. If it does fail, instead of a stock PMD dampener that was probably designed for around 3000 rpm, you now have a dampener that is designed for something closer to 4K, and when the elastomer fails, it is now allowing amplification of the harmonics instead of dampening them. Where you see the stock PMD harmonic balancer mostly breaking cranks in front of the number 2 main, now that same stress point is going to be further back on the crankshaft. When it fails(and they commonly do on heavy cranks) I think it ends up moving the worst harmonics closer to the center of the crank. When it does it’s job it will help over a stock unit, but if it fails it is worse than stock. I know lots of builder’s use those type of balancer’s on engines like a SBF or a SBC, but I think they really do not work very well on a nearly 80 lb PMD racing crank.

JMHO, I’d rather spend the more money for something that does it’s job better, and is lighter weight like an ATI or similar that has inertia rings inside the case of the outer ring.

Do you know what the construction of a BHJ balancer is all about. ?

[Jay S]

There was a question earlier on why you would want a better harmonic balancer than stock if you have light weight internals.

It has been a really long time since I have studied or calculated anything like this, so I am for certain rusty on this topic, but for designing to control harmonic frequencies, I recall starting at the lowest design frequency, then looking at forces during those frequencies in orders, 1st order is where they would start, then 2nd, 3rd..ect. Each order is a multiplication off of the initial starting frequency. With less weight on the rotating assembly you are spreading the orders further apart. If the initial starting place was 700 RPM with stock internals and a stock dampener, it would go 1400, 2100 ,ect. So every 700 rpm. With the light weight internals the stock dampener might move the starting point to 900 RPM. So now it is 900,1800, 2700 ect. It would work the same way with a heavier balancers and stock internals, but from the other side of the equation.

The problem though with the stock balancer is I don’t think you can make the internals light enough to spread the order’s out for many more RPMs. The 2 piece dampeners are supposedly good for about a 3000 RPM range. You could maybe get another 600 RPM’s out of it because the orders are spread out using the lighter weight rotating assembly. But it needs a dampener like a ATI that has a wider operating range combined with the lighter rotating assembly to gain on it much on controlling the harmonics. Plus those harmonics are getting amplified a lot also from more power and more RPM’s.

[Jay S]

Originally Posted by Dragncar

Do you know what the construction of a BHJ balancer is all about. ?

Not totally sure, seems like they add another dimension to the frequency control.

[Half-Inch Stud]

Well, the rattler concept can be applied well to the PMD damper: 9 pockets can house 9 brass cylinder bobs of 3 differing weights. They all fling to the outer pocket wall and bob back and forth in response to accel/decell, and cover many of the frequencies together.

Yea, i designed such for a UAV engine (and did the PMD in parallel ) drafted it, and spec'd out McMASTER Brass for the bobs. Simple machine work, and a cover plate for inspection and a dab of grease. Well, lost interest due to not having a damper problem. Low risk since the "housing" has the diameter and nearly same mass of our PMD damper. A little thicker toward the timing cover.