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Yes - but we're sick of asking ! :-)
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It's fitted to the crankshaft at the front of the engine. Doubles up as a drive pulley for fan belt, air con etc. The bit bolted to the crankshaft is steel, then there's a bonded rubber section, and then there's a heavier bit which has grooves in it for the various belts.
The damper irons out certain crankshaft vibrations, preventing shaft failure due to said vibrations.
Replacement is normally straightforward but might entail removal of any radiators / heat exchangers placed in front of it. (might mean disturbing air con, cooling or pas systems). If the things go pear shaped during replacement, it might mean a new cam belt as well.
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By the way - you can't repair them !
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Yes, practical answer, it needs to be there, can cause great damage when it fails, and on modern engines you can't repair them, because they are a bonded rubber and metal construction, and it's typically the bond between the rubber and metal which fails.
More technical answer - the crankshaft is a long, bent stick, with balance weights and the weights of the big ends and some fraction of the con-rod mass whirling round with it. There are certain frequencies where this system goes into resonance - this is a torsional resonance, with some parts of the shaft twisting a lot, and some parts, typically near the flywheel staying "still". I say "still", because, of course, the whole lot is whizzing around at X rpm, and so "still" is just relative to the rest of the shaft - I don't mean that part of the shaft actually stops dead!
As the crankshaft has mass distributed along its lenght, there are many possible resonance frequencies, each with its own distinctive pattern. By design, most of these possible resonance frequencies are outside the normal rev range of the engine, and so aren't a great concern. However, the first one, the so-called fundamental mode is typically somehere in the usable range. Although the deformation pattern for each resonance frequency is different for each engine type, typically, the first one has a pattern where the nose of the crank twists a lot, and the area near the flywheel remains almost "still". **
Engines with many cylinders have more problems with torsional resonance. For example, a four cylinder four stoke excites the crank torsionally twice per revolution, while a six cylinder four stroke does so three times per revolution. At the same number of revs, the crank of the six cylinder engine is being forced torsionally at 1.5 times the frequency of the four cylinder. Added to the fact that the six cylinder crank is likely to be longer, and hence have resonat frequencies lower in the frequency spectrum, you can see the design problem is much more difficult for the 6.
The device fitted to the crank nose is designed to reduce the amount of twisting, and hence the amount of fluctuating stress in the crankshaft. The outer rim, which also drives the drive belt behaves like a mini flywheel - the rubber sandwich behaves like a spring. In effect, you have a rotary mass/spring system. At one frequency, the mini flywheel, restrained by its rubber spring will resonate in the twisting direction. This resonance frequency is tuned to coincide with the resonance frequency of the crank, thus taking vibrational energy away from the crank, and reducing the amount of twisting at the crank nose.
To call this device a damper is, perhaps a poor choice of term - although I know this is an "official" name for it. I think this, because the device doesn't do any significant damping itself, it's predominantly a reactive device, which would work virtually as well with coil springs acting as the compliant element as rubber.
** For those who wonder why some engines (notably VW VR6 in cars, and Mercedes V engines in trucks, e.g. OM422) have their cam drive burried at the back of the engine near the flywheel, here's the answer!
Number_Cruncher
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Wow. Now that is what I call an answer.
--
PU without his Mod Hard Hat on !
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To expand a little on NC's excellent explanation, the bonded rubber design is perhaps cheaper but less reliable than the design which used to be supplied by Holset to many car manufacturers; these had a cast iron hub keyed to the crank and a gullwing profiled outer diameter. An inertia ring (which had exterior v grooves for belt drives) with corresponding gullwing inner diameter and a rubber member were pressfitted together and seldom failed.
Similar devices have also been used on RWD prop shafts.
(Inertias and rubber stiffness were carefully calculated and tested to damp critical frequencies.)
Crankshaft dampers on truck engines have a thin outer casing fixed to the crank and contain a heavy annular inertia ring, the clearance space being filled with silicone fluid.
For special applications (e.g. the Cosworth DFV grand prix engine) a damper combining rubber and silicone in shear was developed some years ago and proved successful.
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The fundamental issue is whether a defect in a crankshaft damper can be detected by sound:) BS detector on.
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To go a little further, there's one design of crankshaft damper which I think is remarkably elegant.
One potential limitation of the type of crankshaft nose absorber where the two parts are bonded together with rubber is that the device can be tuned to only one frequency or engine speed.
One device that overcomes this limitation is a pendulum mounted from the crank web.
Sorry, my description does include some sums. A pendulum like in your clock has a natural frequency given by
f_n = (1/(2 * pi)) * sqrt (g / l)
where g is the acceleration due to gravity
l is the length of the pendulum
If you mount the pendulum on the crank, the acceleration felt by the pendulum, g, is replaced by the centripetal acceleration
f_n = (1/(2 * pi)) * sqrt ((r*((2 * pi * rps)^2))/ l )
Where r is the radius of the pendulum's mass and rps is the crank speed in revs per second
Now, there's a term that can be taken out of the square root
f_n = (1/(2 * pi)) * (2 * pi * rps) * sqrt (r/ l )
There's a bit of cancelling to be done
f_n = rps * sqrt (r/ l )
So, the pendulum self tunes - the natural frequency of the pendulum increases as the engine speed increases. Once you have chosen r and l, which will depend on the space available, the engine type (2 or 4 stroke) and the number of cylinders, there's no more tuning to be done, and all resonances within the engine's range are covered. Truly neat!
Number_Cruncher
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NC
Who holds the patent?
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OGF
I hope that you are happy now. Question well and truly answered - very helpful.
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It's an old idea, I'm not sure about the patent. I would be amazed if it were still in force.
For more on tuned mass absorbers, see,
en.wikipedia.org/wiki/Tuned_mass_damper (A civil engineering slant)
www.enginehistory.org/NoShortDays/TV.pdf (Historic, aero engine specific)
racingarticles.com/files/general-damper-article-2....f (Some good schematic piccies showing nodal positions)
Number_Cruncher
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Thanks guys, now I know all there is to know. I never had such things on my old cars and never had a failure. Are modern cars crankshafts stressed higher than old car's or is it because it's a diesel?
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I never had such things on my old cars and never had a failure
If you had a car with a BMC 'B' or 'E' series engine, a Hillman, Triumph, Rover, Jaguar or more or less any UK car from 1960 onward you had a crankshaft damper ( I worked at the factory that supplied them)
British built Mini's had them, but the versions licence-built in Europe didn't; as a result some of those did have crank failures and crank bearings wore faster.
As Number Cruncher has explained, straight six engines are more prone to damaging vibrations than engines with shorter cranks, so have all had dampers for many years.
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NC your knowledge of physics astounds me - I did A-level physics and can only JUST follow you! Do you use any reference sources for these posts, or is it all off the top of your head?!
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Alas, most of it is off the top of my head!
However, as I work as a mechanical engineer, very much towards the numerical and analytical end of the spectrum, then the stuff I post is usually quite close to theory I have used in other contexts on non-automotive projects.
In this case, the theory of the tuned absorber was considered when the civil engineering division of a consulting firm I used to work for were consulted over the question of building a tall aircraft control tower. The civil engineers then consulted us. The allowable vibrations levels were very very small, and the site quite windy, and the tower quite tall. We didn't actually win the work, so my calcs on this were never put to the test!
Number_Cruncher
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I had crankshaft damper replaced on my 2000 CRV less than 2 months ago, along with various belts, hoses, and radiator, at the cost of nearly $1600 at local mechanic shop that I had been recommended to and trusted. The engine light had come on. I agreed to all recommended repairs. Up until then, I had every scheduled maintenance and agreed to all services recommended by Honda, done at Honda, save one oil change and a brake job. The other day, the car stalled and I had it towed to the same mechanic. He called and told me the engine seized, crankshaft isn't even turning, and can't tell me why until they take it apart and check. I asked didn't they just replace the crankshaft, he said, "No, the damper. The problem with the crankshaft would be internal. The damper is on the outside."
Should I have this investigated further? I'm afraid to have them replace the engine ($2500) if they are not good mechanics to begin with. I'm surprised that the engine would seize after I had maintained it so well and it only has about 130K miles on it. Should I go to B.A.R.? I don't feel knowledgeable enough to challenge this situation but I also don't want to be taken advantage of and dump more money into the car nor lose it completely. In addition to the new parts aforementioned, it also has new front rotors and tires, so I've put over $2000 into it less then 2 months ago. Basically, I want to know if this mechanic could be responsible for the engine seizing and what I could do to prove it?
Thank you for any response.
Kimisit
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