Harmonic balancer weight

[DaveMcLain]

Balance won't be changed by swapping the dampers because they are both neutral and have no counterweight. A more effective damper will help the engine to make more power but a heavier damper isn't necessarily a more effective one. A lighter damper that is still effective could help HP when the engine is accelerating but make no difference at all at a steady state.

I feel that aftermarket damper selection is mostly guesswork anyway. They might be educated guesses but they are still guesses.

[MadBill]

Extensive tests David Vizard did 20 or so years back on an SBC showed more power (8-12, AIR) even during high RPM/sec. dyno rates with the heaviest (8") damper tested because it greatly reduced torsional vibration and cam mis-timing compared to the lightest or none.

For the serious builder, some companies (ATI for one I think) will instrument your engine and spec out/ build its ideal damper.

Fun fact: Running an engine at its crank resonance RPM for more than a few seconds can spike the oil temp by 20°or more.

[DaveMcLain]

Fun fact: Running an engine at its crank resonance RPM for more than a few seconds can spike the oil temp by 20°or more.

That seems extremely dubious.

[MadBill]

It was in the article I mentioned re custom dampers. They talked of the need to run the engine at its resonance point(s) for long enough to get good data, but being cognizant of the rising risk of crank failure as signaled by oil temperature increase. (Imagine rapidly bending a 50# paperclip back and forth..) If I can find the article again, I'll post it.

[roc]

Fun fact: Running an engine at its crank resonance RPM for more than a few seconds can spike the oil temp by 20°or more.

That seems extremely dubious.

It was in the article I mentioned re custom dampers. They talked of the need to run the engine at its resonance point(s) for long enough to get good data, but being cognizant of the rising risk of crank failure as signaled by oil temperature increase. (Imagine rapidly bending a 50# paperclip back and forth..) If I can find the article again, I'll post it.

You may wanna call it Fun Article then, which isn't synonymous of Fun Fact.

[fastvette]

So then why do sprint cars not run one?

[pamotorman]

So then why do sprint cars not run one?

because they do not run at a constant RPM. the go thru the critical harmonic spot quickly

[ZIGGY]

So then why do sprint cars not run one?

because they do not run at a constant RPM. the go thru the critical harmonic spot quickly

Direct drive water pumps help dampen as well.

[dwilliams]

Most of the time the dampener didn't fit the crank

Wait until you get a balancer that's .003 or .004 undersize instead of .001. For some reason I ran into a bunch of those a while back, all aftermarket, different brands. The installer tool strained putting them on... and then the pullers just gave up trying to remove them. I wound up having to make some heavy duty pullers to get them off.

Now any non-OEM balancer gets miked and meets up with the rod hone if it's undersize. I have a stone dedicated for that particular use.

[DaveMcLain]

It was in the article I mentioned re custom dampers. They talked of the need to run the engine at its resonance point(s) for long enough to get good data, but being cognizant of the rising risk of crank failure as signaled by oil temperature increase. (Imagine rapidly bending a 50# paperclip back and forth..) If I can find the article again, I'll post it.

If the crank was heated to glowing red hot I doubt it would heat the oil 20 degrees within seconds, nonsense.

[engineguyBill]

It was in the article I mentioned re custom dampers. They talked of the need to run the engine at its resonance point(s) for long enough to get good data, but being cognizant of the rising risk of crank failure as signaled by oil temperature increase. (Imagine rapidly bending a 50# paperclip back and forth..) If I can find the article again, I'll post it.

If the crank was heated to glowing red hot I doubt it would heat the oil 20 degrees within seconds, nonsense.

Yeah, I don't buy that either.

[DaveMcLain]

It was in the article I mentioned re custom dampers. They talked of the need to run the engine at its resonance point(s) for long enough to get good data, but being cognizant of the rising risk of crank failure as signaled by oil temperature increase. (Imagine rapidly bending a 50# paperclip back and forth..) If I can find the article again, I'll post it.

If the crank was heated to glowing red hot I doubt it would heat the oil 20 degrees within seconds, nonsense.

Yeah, I don't buy that either.

What I would buy is that the RPM level where the crankshaft got into natural resonance just happened to coincided with the RPM where their oil pan allowed the assembly to start really picking up and holding onto the oil from the sump. Then they might see a rather rapid temperature rise in the oil but also a great big loss of horsepower.

A few times I've mentioned an idea to Kevin at Performance trends and he didn't think it was possible to do at a reasonable price: Have a box that you could hang on the dyno with two pickups, one to sense the ring gear teeth and another to sense a reluctor wheel that's bolted to the front of the crank. The box would send data to a PC where the phase angles between the teeth could be compared during a full throttle dyno sweep. After some tests the relative efficiency or lack thereof of the damper could be measured. He didn't think that building a box that could handle say 165teeth at 7500rpm would be cost effective.

[amcenthusiast]

Sorry to read and discover so much confusion.

It's not really people's fault though when there's so little information on this topic 'out there' on the Internet.

(please take no offense; rather consider how we all enjoy SpeedTalk tech info because we enjoy learning)

Trust me; if you made your own custom welded stroker crank... you might make an extended search to learn all you could about 'harmonic dampeners' and/or 'harmonic balancers'.

...this is partly why I'm posting my 'AMC 327 - 443 XRV8' engine build on SpeedTalk's 'Show and Tell' section. (I think y'all might enjoy it for all the technicalities involved with making the custom-experimental race engine)

The most authoritative article I know of pertaining to this man's particular question is found on EPI.com webpages:

http://www.epi-eng.com/piston_engine_te ... orbers.htm

(Please read his insightful webpage on crankshaft design also)

I think the next most informative article on this topic might be found here:

http://performancedevelopments.com/pors ... nefailure/

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In summary, EPI is saying it's not called a 'harmonic balancer or dampener' at all; it should be called a 'torsional absorber'.

The logic is that the larger scope of harmonic vibrations caused by the spinning crankshaft are dampened many ways (those vibrations are transferred into the entire engine as a whole unit: not merely into a weighted ring attached to the snout of the crank itself) ...the engine block itself, even the water jacket, plays a significant role in dampening harmonic vibration caused by the rotating assembly (hence some of my explanation about 'block filler' installation on the AMC 327 - 443 XRV8 thread)

Wherefore, it's the torsional twist harmonic vibrations stemming from the crank is what's more important.

NOTE: distinguishing the type of motion is the key issue; torsional vs centrifugal... as I understand it.

At this point, I have no desire to embarrass anyone for what I would define as 'innocent by ignorance', so I will choose to end my explanation pertaining to this thread here.

[1972ho]

Well looks like the front snout of my crank broke off today,I was making a few tnt runs and I could hear the engine missing in high gear and on my last run it started to miss early in the run and then I hear a kind of bang.And get towed back to pits and see that my dry sump pump belt is missing and then I see that the balancer is moving around and find that crank is broken just right behind the balancer near the crank cam sprocket.Well that didn’t last to long.

[FC-Pilot]

Out of morbid curiosity which balancer were you using? I understand that it may not have been its fault, but still curious.

Paul