Crankshaft torsional dampers

[morrisnutter]

I'm mid way through designing a new crank for my track car, but I want (need?!) to add a torsional vibration damper. The front end of the crank is open to a fair bit of change to suit. Does anyone know a supplier or manufacturer of these items so that I can ge tone which will suit the aplication?

It's a long-shot, but worth asking!!

Cheers

Paul

[boyracer]

Just my 2 cents worth.
I'd be looking around the paddock to see what everyone else is running and ask "Do I really need one ?"
Used to race an old Datsun 180B which produced reasonable horsepower and reliably. Never had a damper on the front of that, pulley on the front was solid mounted. Never seemed to bother it.

I guess it depends on application as well, if you're putting lots of horsepower thru a small crank, every thing you can do to help it is a good thing.
An Australian sight that sells all types of dampers, might be worth a look just to see what's out there.

www.rosstuffbond.com.au

[THR]

ooo explain this damper thing a bit more ive never heard of such a thing!!!
(or called sumin else!?)

designing your own crank?! brave?/???? or have experience?

[StephenRae]

Can't help you to find a 'damper' but I would suggest that if you are unsure whether one is needed or not then you may not yet be ready to design your own crank...

[graham bahr]

Originally Posted by THR

ooo explain this damper thing a bit more ive never heard of such a thing!!!
(or called sumin else!?)

designing your own crank?! brave?/???? or have experience?

lots of engines have a harmonic damper, if you look at an engine with a front pulley which is far bulkier in terms of size and mass than it needs to be its probably a damper, a closer inspection will probably reviel that its in fact two parts which are bonded together with a fairly thick layer of rubber, the idea of this is to allow bad vibrations which could poteintially break the crank or at least cause nasty vibrations to be damped out as the two metal parts of the pulley can move a little relative to each other.

a crankshaft is a very complex piece of equipment and to behonest succesfully designing one for a car engine is unlikely to be achived by anyone other than those who already know what they are doing, however if were only talking about moving the stroke or pin size on an existing crank that maybe another matter

[Peter McKinley]

Crank Dampers

Is your engine al inline engine or V8. In line i wouldnt worry about so much as there is no crank pin offsets to cause torsional oscillations of the crank. Only recently have in line engines been employing dampers. With all the auxilliary services that the crank drives power steering, water pump, alternator, air con cmpressors etc there, in themselves they provide a degree of damping. However in a V8 the story is different. There are two suppliers of these based in USA, one is Fluidampr and the other is ATI the Fluidampr is a silicone filled unit and the ATI rattler unit is an elastometric unit, both used by any of th american V8 competitors. Info on them can be found on the web and the reasons you should use them. i knlw of many competitors using V8 rover engines in competition cars , single seaters and saloons. Most if not all have shortened the nose of the rover crank and thrown away the stock damper. From talking to sme people it appears they get away with it because most engines are being driven well up the rev range and the torsional angular displacement acting on the crank becomes less when idling or pottering around the crank experiences a much bigger angular movement between its pins. Hope the above is useful, but look up the websites above
Regards

Perer

[Peter McKinley]

Distributor in the UK for Fluidampr is Roadcraft, , at 44-01903-522900.

[greenamex2]

I had to removed the crankshaft damper on my race car because it and the flywheel kept breaking the crankshaft. Not had a problem since!

[Tim Falce]

Originally Posted by Denis Bassom

I had to removed the crankshaft damper on my race car because it and the flywheel kept breaking the crankshaft. Not had a problem since!

How do you know this was the problem?
I have trashed 3 engines with what I thought was damper problems, i.e. the rubber broke up and the dampers fell apart. After a chance phone call I was told to check the clutch and found the problem of the plates that hold the main pressure plate to the housing were bent and put the clutch out of balance.
Maybe you could shed some light on this as I don't want to buy any more cranks as I have broken one and buggered 2 more up in the past 3 years.

Originally Posted by Peter McKinley

......Only recently have in line engines been employing dampers...

Jaguars were fitting them from at least 1948 on the XK engine and I am pretty sure my Pinto engine of 30+ years ago had one.

[graham bahr]

it was only the later pintos that had crankshaft dampers,

although i cant be totally sure but i think it was only the injected ones even then that had them.

[Tim Falce]

I had an 1800 in a Sierra that had a damper although that was the American engine that was no good, burnt more oil than petrol and just fitted to them to get rid of the stock of discontinued engines.

[greenamex2]

falcemob - My ex-McLaren engine builder talked to the crank manufacturer (Doug Kiddie Engineering) and between them worked out that the crank was designed for a very lightweight flywheel, clutch assembly and damper. Everything else had been checked and replaced SEVERAL times (including three billet steel cranks).

In short the weight of the extraneous bits versus the torque (such as it was) of the engine were shearing the crank pins.

I also had the standard crank damper pull apart, but this is normal on Corolla's!

The root problem with my engine is the revs I run it to (9500) on a wet sump. It really can't cope but it is the only way I can beat the much ligther and better handling cars I race against.

[morrisnutter]

Thanks Peter! I'll chase up those links when I get a quiet minute at work

Designing the rest of the crank shouldn't be a problem- I pass my days as a development engineer for a major Tier 1 OEM supplier in the automotive engine field...

For the record, the engine is a straight 4- actually from a 1935 Riley which I'm planning to run without flywheel (+ some other tricks) hence the need for a redesign of crank to maintain the balances.

Thanks for the tips!!

[Peter McKinley]

have a look at this site - gives a good explanation of torsional dampers
http://www.grapeaperacing.com/GrapeA...gs/dampers.pdf

[dtype38]

Peter's reference above is a decent introduction, although I think it might be being a little unfair to "harmonic balancers". I think that is a name sometimes misused to mean "harmonic damper" or "harmonic detuner" which simply suggests a narrow frequency band damper aimed directly at the resonant frequency of the object (in this case crankshaft) ie., nothing to do with crank balancing .

Anyway, the point (as described in the above link) is that when its running, the crank has rotational vibrations going through it. If those vibrations happen to match any of the major resonant frequencies of the pulley/crank/flywheel/clutch assemby for any length of time, then bye bye crank. That means that a damper is important, but not necessarily essential, and then only if it works over the right frequency range. The moment you move away from the original manufacturers design (assuming its not from the dark ages ) with, say a differently heat treated crank, or different weight flywheel and front pulley, then the resonant frequencies will change. Only a lot of testing or calculation will then tell you if the original damper is still any good, or even needed at all. A dramatic change to the materials and weight of the system might even push the resonances out of your normal working range and you can throw the damper away. Or it might put them smack in the middle of your power band and you'll have trouble getting any crank to last.

My advice FWIW is that if you don't have access to proper methods and equipment to design and test drive train parts, then stick to parts and assemblies offered by reputable tuners of the engine you're running. They will normally have lots of test hours on their parts and will have reasonably well matched components. Throwing bits away and cutting lumps out of flywheels at home may well work, but I would guess only in a minority of cases.

[dtype38]

BTW, I don't actually agree that an elastomer damper works simply by absorbing energy and disappating it as heat by distortion of the elastomer. The elasotomer also acts as a damped spring allowing the outer ring to "wobble" in its rotation and act as a harmonic detuner as well.

[graham bahr]

Originally Posted by dtype38

BTW, I don't actually agree that an elastomer damper works simply by absorbing energy and disappating it as heat by distortion of the elastomer. The elasotomer also acts as a damped spring allowing the outer ring to "wobble" in its rotation and act as a harmonic detuner as well.

i'd have to go along with you on that one d type

[icemachine]

Morris, if you work for a tier 1, just buy you're FEA guy a nice Steak dinner, and then mention you got a new model you'd like him to run

[morrisnutter]

Originally Posted by icemachine

Morris, if you work for a tier 1, just buy you're FEA guy a nice Steak dinner, and then mention you got a new model you'd like him to run

Ha- already done that (if you substitute a crate of beer for a steak dinner
) The difficulty is those nasty torsional natural frequencies appearing somewhere in the rev range of an otherwise (relatively) good design, hence needing to get round them somehow!



The way this sort of damper works is by the outer ring being effectively isolated from the crank system at most rotational speeds. They are designed such that at a given speed (or range of) the silicone fluid cannot shear anymore, so then the outer ring then becomes part of the vibrational system. The effective extra rotating mass has the effect of changing the torsional frequencies of the 'new' system over the dampers operatinal range.

So, in terms of rotating components, you are 'adding' an inertia component mid operation. A very neat trick indeed

[icemachine]

Hm sounds interesting but instead of just using silicone fluid I'd look at using one that is a Magneto-rheological (MR) fluid. With instantly adjustable viscosity your dampning would be much smoother

[enlashok]

Interesting idea with magnetic fluid alltho completely unusable in his application.... would be interesting to fool around with that on the design side would need some sort of electronic controll.

[dtype38]

Originally Posted by morrisnutter

The way this sort of damper works is by the outer ring being effectively isolated from the crank system at most rotational speeds. They are designed such that at a given speed (or range of) the silicone fluid cannot shear anymore, so then the outer ring then becomes part of the vibrational system. The effective extra rotating mass has the effect of changing the torsional frequencies of the 'new' system over the dampers operatinal range.

I'm a bit confused as to how the fluid is maintained sufficient shear to keep the outer ring locked at a given rpm. Is the shear not generated by crank acceleration rather than speed (like in a torque converter)?