knife edge crank

[ablesnead]

No ,absolutely not saying it....just wishing we had an in depth dialogue as to why or why not...seems like just getting easy answers...similar things as in other threads that ended up teaching us the difference between science ( art ?) , and old wives tales .

[TimZ]

 

I thought the damper was for harmonics damping, not balancing.  (Edit - semantics, maybe..)

 

 

That's correct and no it's not semantics - they are not the same thing.

 

Take a look through this thread for some discussion on this:

http://forums.hybridz.org/topic/15727-l6-dampner-problem-help/page-3?hl=bell&do=findComment&comment=116851

[NewZed]

Thanks for the link.  That should help the OP out if he reads through it.

 

The semantics problem is general to dampers around the auto world, I think, as you noted in  in the link, since it's often referred to as a "balancer".  The idea of "damping" energy is uncommon and misunderstood, and harmonics hard to understand, so we end up with dampners and moistening devices.  Not claiming to feel super comfortable talking about harmonics myelf, to be clear.

 

As far as harmonics and the L6, I wonder if the Porsches and VW's the OP refers to are 4 cylinder engines.  Different harmonics maybe?

Edited May 30, 2013 by NewZed

[Tony D]

hot rod VW's use aluminum pulleys across the board.... jut say'in

 

You are SORELY MISINFORMED ON THAT POINT! Taking the absolutely wrong thing away from what you're seeing there, no depth of knowledge on what/why and drawing a conclusion.... Bad form!

 

Universally the REAL Hot VW Racers (guys running long term engines, and not tear them down and replace the crank after 25 runs drag cars) run HEAVIER THAN STOCK pulleys. In fact, The Berg Equalizer Pulley weighed in about 8-10# as I recall, and was INSTRUMENTAL in keeping flex in the VW cranks from being an issue in breakage. As usual, others copied him.

 

But if you think those "lightweight aluminum pulleys used across the board" are ACTUALLY LIGHTER in either total mass, accelerated mass with relative MOI, or in ANY WAY are anything but a place to mount your degree wheel with the special glue they sell....YOU'RE HIGH! Go weigh the STAMPED SHEETMETAL STOCK VW pulley and weigh any of the cast or Billet Pulleys out there. I can tell you which one weighs more.... And it ain't stock! Those aluminium wheels were there for one thing: you can put a degree wheel on them and set total advance with a static timing light, and have them machined to fit a 'Sand Seal' -- they don't fly apart at 10,500 rpms like the stock non-oven brazed cooling fans and Sheeetmetal Stock Pulleys do, either (at least if you get a GOOD one, and not some cheaply-cast Taiwan Knock-Off...)

 

And WEIGHT on the back end of a VW engine is what was needed. They didn't (counterweight) balance them stock as they were limited to 4000rpms, when you wing them to 9,500 you start breaking things--hell, in fact if you wing them to 5,000-5,500 you WILL break the #3 Cylinder Mounting Boss in the case and pound out your mains to the point where you can't hold oil pressure at idle no matter HOW big an oil pump you stick on it! And cranks be another one of them. Using a VW Engine with a 12" long crankshaft as a basis for what you will stick on the end of an almost 30" long crankshaft borders on the criminally .... uh.... maybe it even crosses the line into blatantly, criminally misinformed misdrawn conclusion mongering!

 

Just Sayin': THINK about what you're saying. That was a damn ill-thought out statement to make in both function, form, and fact. It's unsupportable, and factually wrong in the case of VW's. Coffey can talk to his business partner and get the scoop on P-Cars, but I figure it will go along these same lines.

 

75,000+ miles on a 175 HP VW Flat Four, Berg Equalizer, 12# Flywheel, no center main pound out, no oil pressure problems, no oil leaks from a flexing center main joint on an AS41 Case here talking back about this VW "Universal" application.... Dude, you are so wrong on that. SO wrong!

 

A BoxerSix and a Flat Four got crank legnths about HALF the legnth of the L-6. Think!

 

<I edited this to temper my original comments to something less confrontational.>

Edited May 30, 2013 by Tony D

[ctc]

Go to the BHJ damper site and read all about it. Dampers on a datsun are for torsion issues (harmonics) on a properly balanced (rotational mass) crank. There are many threads here about the BHJ dampers and how they work as well.

 

Saying what others are saying, stupid phone clipped the last few posts.

Edited May 30, 2013 by ctc

[TimZ]

 

<I edited this to temper my original comments to something less confrontational.>

 

 

We really need a "Spittake" emoticon.  Just sayin'.

 

<edit> found one...

 

Edited May 31, 2013 by TimZ

[duragg]

Don't the dampers dampen some of the relative vibrations between the crank and accessories too?

Akin to motor mounts or clutch springs allowing differently mounted and acting components to all live in harmony and each allowed to do its own thing and not transmit as much negative energy to adjacent components. Sorta like TonyD putting just a slight damping on himself (Very impressed and duely noted btw Mr D.) I hear birds chirping! Huh?

 

 

(edit..  Eh, now I feel like I am missing something Tony.. Kinda like an all Christian Reddit.  Just not the same).

Edited May 30, 2013 by duragg

[ablesnead]

The posted previous thread on dampers was just what I was looking for ....sorry if my lack of  information has offended , I did try the search function, but obviously not thoroughly enough .... the point on solid aluminum pulleys is that they lack damping material...thanks all for the insight..Tony you are a ******* arrogant ******* !

[skirkland1980]

A good video to watch on YouTube is the one about how Ford started using turbo chargers in formula 1 in the 80's. They learned a good lesson about harmonics. Steve Morris runs engines without a dampener. I'm wondering if it's the huge supercharger belt the does the dampening?

[Tony D]

Don't make me the bad guy for instructing you on your poor skills on observation.

 

One of the key reasons VW's used Aluminum Pulleys was they are easily machineable, and racers could make them UNDERSIZED to save horsepower during drag racing. (Underdrive Pulleys well before the current crop...)

 

The fan on the VW soaks up power huge...

 

That is the point on VW engines, not that they are solid. 

 

The POINT on VW's is they were a 4,000 rpm engine. Therefore running solid pulleys. 

 

And that when you REALLY started turning over 5,000 to prevent flexure breakage, you DID ADD A DAMPNER. (Look Up the function of "Berg Equalizer" in your supposed searches before you get mad and someone who actually knows what is going on in a mis-cited reference...)

 

http://www.geneberg.com/cat.php?cPath=7_222

 

EDUCATION, not mere observation is the key. Don't be so resistant to learning, listen to someone when they tell you that your idea is fooked. Because that's how you learn.

 

Gene Berg was big on education... Look at his catalog page, what the design of the part was drive by, what their testing revealed, how it saves you money in the long run and what it does. Education of the customer, key to Berg's success... And another guy that shut you down on the phone and hung up if you didn't have invoice numbers to prove you deserved his support. Some would call that being a " ******* arrogant ******* " today as well.

 

Read the link carefully.... It goes OPPOSITE of what you THOUGHT was an impetus for choosing it. This is engineering, it's not rocket science, but it does require thought and some of it is more than mere intuition...

Edited May 31, 2013 by Tony D

[ablesnead]

With the help of the posts from 10 years ago on this site and a lot of reading on google , I think I have a handle on my questions , unfortunately I don't know if I have a solution...Smokey Yunick once told me that a 350 inch chevy needed 167 hp to spin the engine before putting power to the ground....I can't really quite grasp those numbers, but the concept of freeing up horsepower when the basic engine , as an air pump , had limits on its ability to make it , has always intrigued me . Contrary to the little difference one responder to my original post noted , I experienced a completely different feel in the IMSA porsche that I drove at the 24 ,  So now years latter my hobby car is limited by its factory efi intake in a normally aspirated form . Knife edging, lite fly wheels, lite clutch pak , are all tools I plan to use to put more of that limited power on the ground....so now we face the harmonic problem...no one addressed it specifically . Tony ,  in what I find , is a rude and overbearing way , uses an example of a hot rod vw engine that doesnt need a damper at the OE designed operating range , but a builder that is widely respected does address the problem with his modified engines......I found many likewise respected builders that did not subscribe to Bergs theory , I know on our 50,000 dollar GTU engines we never adressed it either...I now think that was a significant mistake . I think with our L6 we are still making that mistake...Note: one poster claiming intensive research quotes a harmonic between 72 and 75 k , Tony , in other threads makes lite  of the " so called harmonic at 73 k  , he has real world experience spinning a crank with stock rods to 9k...well thats the whole point....If a stock damper is designed for 6.5 K of therebouts , you essentially don't have a functioning one at 9 k.....Since any modification of the reciprocating mass needs a damper designed for that particular mass , to be effective , anything except a possible fluid damper alternative is just a sort of voodo bolt on....in the same vein as bigger throttle bodies....I wish sharper minds than me could apply thought to dampers that really are designed to be modified for our individual builds.... because if we say ifs not important  then , the choice to run no damper at all , by default, is also not important . John lightened his crank from 51 to 32 lbs I believe...lite rods, lite pistons...you get my drift. no off the shelf damper  would fit all cases..Apparently any damper that doesn't fit a prescribed resonance range offers no benefit and a wandering timing mark...note  boxer engines by their design have a much lesser concern than we should . I really enjoyed this  THANKS

[ctc]

Don't know if you found this in your searching, but good description of what goes into driving the crank harmonics.  They can also direct you to what damper and frequencies you need to address.  You might want to give them a call.

 

http://www.bhjdynamics.com/index.php?main_page=page&id=4

 

I should also add that you need to be careful when applying American V8 tech to these engines.  Mass produced Chevy's and Ford's are different animals compared to a long inline 6 cylinder with much different design principles.

 

Use your V8 knowledge at your own risk with these engines.  Some areas it applies, some it does not.

Edited June 1, 2013 by ctc

[Tony D]

"I should also add that you need to be careful when applying American V8 tech to these engines. Mass produced Chevy's and Ford's are different animals compared to a long inline 6 cylinder with much different design principles.

 

Use your V8 knowledge at your own risk with these engines. Some areas it applies, some it does not."

 

Amen, brother, that goes for ANY other engine!

 

As for taking things out of context from prior posts of mine...like your observations on the VW engines YOU cited (my citation was countering your bad observation and post)...don't put words in my mouth as to what I said, or draw conclusions on the entire engine package that I have NEVER STATED DETAILS UPON SAVE VERY SKETCHY ONES AT BEST!

 

Your ability to draw the wrong conclusion out of clearly stated things I HAVE said, though...is astounding.

 

You go ahead and piss as high on the fence post as you desire. There is engineering and thought involved in this, and you're not going to dumb it down to generalities.

 

And cross posting from other makes, marques, and impressions as a driver is really just background noise.

[ablesnead]

Ditto.

[tooquick260]

I don't know much about this, but my dad had the Berg equalizer pulley on his 58 ragtop bug. On his nitrous setup 13:1 compression he left the starting line at 10,000. Shift light was at 9,400 rpm. Never had a bearing problem. Now nitrous blow ups yes!!!!

 

 

One of his video's.

 

http://s158.photobucket.com/user/melbellwood1/media/MOV01367.mp4.html

 

 

 

He said you can make em run. His had counterweighted crank and stock does not. But many would run stock cranks and turn that rpm but would tear down after each event, either replace just the bearings or replace block in its entirety. 

 

 

So from what all are saying. Do you recommend a balancer or not for our L series engines?

[TimZ]

 

So from what all are saying. Do you recommend a balancer or not for our L series engines?

 

A harmonic damper - and yes.

 

To address a couple of other items from previous posts - 167hp loss from a 350 sbc is way too high if we are talking about frictional losses and such.  This number is almost certainly referring to the energy available in the fuel vs. how much comes out the crank.  Unfortunately a great deal of this is due to the thermodynamic efficiency of the Otto combustion cycle itself, and there isn't much you can do about that, aside from relatively small improvements from compression ratio changes or changing to Diesel or Miller cycle, or something similarly impractical.  None of them are going to be anywhere near 100% efficient.

 

I concur that a great deal of effort went into the BHJ damper and it is a really good investment so long as you are using the crank(s) it was designed for.  Tony - I'm assuming that this was the diesel crank - is that correct?  Do you know if the tuning is similar or the same for the Diesel vs the "normal" L28 crank (or L24 for that matter)?

 

To my thinking, Ablesnead did raise a legit question regarding how tight a tuning match is really required between the damper and the crank, and how much does the crank's resonant frequency change if you remove significant mass and possibly stiffness from it by knife-edging it.  Offhand, I would think that knife-edged cranks like some I've seen on this forum might have significantly altered resonant frequencies, and it might not be intuitive as to how they were altered.  Thoughts?

Edited June 2, 2013 by TimZ

[NewZed]

Seems like there are three topics in play, and all blended together.  Contoured counter weights for improved oil windage purposes (knife-edging), lightweight crankshafts (a side-effect of kinfe-edging), and harmonic dampers (got thrown in from the side from Porsche and VW land, although it should be considered when crank shaft weight modifcation is done, re the BJH white paper [which is well worth reading]). 

 

The original question was a little bit vague, and referred to the effects of losing crankshaft inertia (motorcycle-like response) unless he was implying that oil film drag was slowing the engine's ability to rev quickly.  Seems like the purpose of knife-edging has been mis-defined a little bit and thrown the thread off-topic.  From my limited understanding of all of these things.  

[Tony D]

Hell, nobody mentioned crank scrapers yet...

TimZ I'm not following the LD query... The citing of my "making light" of the big bugaboo harmonic (and EVERY TIME I've mentioned it) has been within the well-known engineering context of critical speeds...which has gleaned supporting comments in the past from many others. To wit: a harmonic or critical speed in ANY rotating machinery is worked around in a few simple ways:
1) Operate BELOW the critical speed (VW... Most engine manufacturers)
2) accelerate THROUGH the critical to the generally broad band in between the first and second critical and operate there (High Performance L-Engines)
3) Add devices to dampen nodes to compensate for longevity (Sulzer Container Ships operating in the hundreds of rpms, with 45' crankshafts and harmonic pulsations that change web deflection on the crank throws!)

The key to any harmonic issue is a simple one: DON'T DWELL AT THAT SPEED RANGE!
Setting up a car to dwell at 7,300,~7,500 for several seconds a lap is just asking for trouble. Some would say its downright stupid setup.

I pooh-pooh the harmonic because I comprehend this simple fact, and have enough cognitive and reasoning ability to accelerate THROUGH any bugaboo areas so that it NEVER causes me any concern. Ever. It becomes, in this context, a non-issue, something for bench racers and theoreticians to obsess over in the interwebs chat forums.

I accelerate through the area quickly, and am not so stupid as to not avail myself of any longevity-increasing devices on the market.

I have NEVER said not to run a harmonic damper. I HAVE, however said it was stupid to run with a solid pulley if you are going through or anywhere near the areas where problems can be produced.

 

<EDIT> The dampner will wear out if 'worked' by dwelling in the rpm range... something has to wear when you do it, dampner or crank. Really the way the tuning goes you just have to be "close" to affect the dampning effect. If you are cognizant of the fact you don't DWELL in or near the problem speed areas, it really doesn't matter as the dampner will mask the stuff well enough in most applications that it doesn't do damage. Our first Bonneville Engine had a power peak, with Webers of 7,500 rpms. Stupid. The dampner was CONSTANTLY working loose, fretting, wearing out. Changed induction to ITB's and ran at 8,000+ for four years with a dampner and nut that was removed inspected and reinstalled for the next four years. With the Webers, we had to retorque the bolt, with loctite, every weekend. holding at 7,500 for a minute straight rattled things loose and the dampner insert was HOT after a run. HOT HOT. The guy running the LD Crank (I think) is Burton Brown... Then again, he may just be running an offset ground stroker like Dave does from time to time (and more often of late it seems...) He was shifting well before 7,500 in his Bonneville Record Run. Don't know what's on the snout of his engine, but I'm betting coming out of Dave, it's not an aluminum underdrive pulley setup. That's why you machine the new pulley for the alternator...

 

Watch, now someone will draw a conclusion that Webers wear out your harmonic dampner.

Edited June 2, 2013 by Tony D

[skirkland1980]

Question about dampers: why is the early 75-76 damper smaller than the later (1983) damper? Is there any advantage of one over the other?

[TimZ]

Hell, nobody mentioned crank scrapers yet...

I heard TonyD say one time that crank scrapers give you an extra 1000 rpm of resonance!  

 

My thinking on the LD question was that the damper is a tuned mass mechanical filter, that was tuned to damp some specific range of mechanical vibration frequencies.  My mental picture is that it's a notch filter of sorts, with the notch tuned to the resonant frequency of the crank.  So when BHJ designed their crank damper, my recollection was that they tuned it to match the characteristics of a fresh OEM damper (my recollection could be faulty on this - open to corrections ).  

 

What I don't have a good feel for is the characteristics of the filter - is it relatively narrow band with high attenuation, or does it damp a wider range of frequencies with somewhat less attenuation, or something else?  My assumption here is that the damping bandwidth is likely sufficiently wide to cover the variety of cranks that it will likely be attached to, within reason.  So then the next thing that occurred to me was that a knife-edged crank might not fall into the "within reason" category if it's resonant peak has been sufficiently altered (again I'm _assuming_ that this is a possibility).

 

Does that make sense or am I off on a tangent?  Main thing I was trying to get a warm fuzzy feeling on was how robust should we expect the damper tuning to be to variations in crankshaft selection (say, non-knife edged L24 through LD28).

 

Also TonyD, why do you hate Webers so much?  I heard you say one time that they destroy cranks or something...