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Are Harmonic Damper needed on Flat Six?

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Are Harmonic Damper needed on Flat Six?

Postby JustinOlson » Tue Sep 08, 2009 11:27 pm

From my reading, flat six engines are balanced due to there geometric configuration of opposed cylinders.

"In the horizontally-opposed or boxer configuration, the two halves are mirror images of each other and the directly opposing pistons are moving toward each other or away from each other at the same time. The two motions cancel each other. Hence the engine is in perfect primary balance. Straight-3 engines have no secondary imbalances, so all you are left with is an intrinsic tertiary vibration caused by the fact there are only three cylinders firing per crankshaft revolution."


My question is do I need a harmonic damper on a flat six engine? I'm hesitant to just throw on a aluminum crank pulley on my engine for fear of premature wear.

Regards,
Justin
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Justin Olson
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Postby Piledriver » Wed Sep 09, 2009 1:38 am

There still may be harmonics at certain RPMs that you may want to dampen out, but the "harmonic balancer" will typically just be a very heavy, balanced pulley on any boxer.

If the manufacturer didn't put one on, it probably isn't needed, and may actually create issues.

IIRC the Corvair crank does have some particular RPM//harmonic that should be avoided, and I do believe they make dampers for those, but it's another "nice" thing to have and not usually required..

I once saw a T1 VW motor set up with a very lightweight flywheel ...and a 6 lb crank pulley. These aren't active dampers, just heavy pulleys... and the pulley end really only has a woodruff key to keep things straight and is prone to cracking there, no taper.
(Any hipo T1 will have a fully counterweighed crank with additional mass, so adding more to the weak snout is probably counterproductive IMHO)

Looked cool, but I'm skeptical it did more than that, and perhaps less.

They DO make V8 style dampers for T1 VW motors IIRC, but they are very seldom used, and probably even less often actually required.

I don't recall ever seeing a huge damper on a 911, the fan pulley is typically pretty small dia.

What's your application?
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Postby Lazy JW » Wed Sep 09, 2009 10:16 am

The late Gene Berg did extensive R&D work on Type 1 Volkswagens; he was the one who developed and recommended the heavy crank pulleys. His theory was that the heavy pulley dampened the vibrations that would otherwise run back down the crankshaft and cause excessive case/bearing wear. I have no personal experience because I never run anything but stock in my VW's so never made enough power to get into that realm. Gene, on the other hand, made enough VW power to cause all sorts of mayhem.
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Postby JustinOlson » Wed Sep 09, 2009 1:10 pm

My application is a Subaru flat six out of a SVX. (3.94" bore, 2.95" stroke). Fully counterweighted crankshaft. From the factory it comes with a harmonic damper. The redline for this motor will be between 9000-9500 maximum.

Here's a picture of the engine:

Image
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Postby Unkl Ian » Wed Sep 09, 2009 1:50 pm

I think the "need" for a harmonic damper
is related to crankshaft twisting and bending.

Street/endurance applications, I would keep it.
Your crank bearings will thank you.
Just because you never studied the Laws of Physics,
doesn't mean they won't try to kick your ass.
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Postby PackardV8 » Wed Sep 09, 2009 2:01 pm

You've answered your own question:
From the factory it comes with a harmonic damper.
Seldom to never does an OEM spend a nickle they don't absolutely have to for durability.

thnx, jack vines
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Postby JustinOlson » Wed Sep 09, 2009 4:01 pm

My next question is regarding ATI super dampers. Are they tuned to a specific engine? Could I effectively use one of their 4 cylinder Subaru dampers on my 6 cylinder?
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Postby Ron Golden » Wed Sep 09, 2009 4:41 pm

My partner and I are building a 12,000 rpm SB Chevy and ATI designed the balancer for this engine. I'd at least call them and get their response.

Ron
Last edited by Ron Golden on Wed Sep 09, 2009 10:45 pm, edited 1 time in total.
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Postby Masher Manufacturing » Wed Sep 09, 2009 4:49 pm

Some factory Corvair testing.

http://www.dalemfg.com/dale_026.htm
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Postby JustinOlson » Wed Sep 09, 2009 8:22 pm

Masher Manufacturing wrote:Some factory Corvair testing.

http://www.dalemfg.com/dale_026.htm


Thank you for the link. That is very interesting!


I called ATI and they will build me a custom damper for about $700.
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